Immunology | Immune system| Immunity

Significance of fertilization

1. It stimulates the secondary oocyte to undergo second maturation division to release second polar body and to form haploid ovum.
2. It restores the diploidy in the zygote.
3. Fertilization membrane prevents polyspermy.
4. Metabolic activities are increased as more mitochondria are available.
5. It combines the characters of two parents and introduces variations.So helps in evolution.
6. Centrioles of sperm form spindle to initiate the cleavage of zygote .
7. Sex chromosome of sperm is either X or Y and helps in sex determination.
8. Copulation path sets the axis of division.

Some of the other importance of  fertilization

1.It rises to formation of a new organism/In case of plants it develops into a fruit.
2. It is the successful formation of zygote by the fusion of sex_ germ cells that are female and male gametes.
3. It leads to a successful reproduction attempt.
4. It ultimately leads to a replication of a new organism as an offspring.

Fertilization

Fertilization involves the fusion of haploid male and female gamete to form diploid zygote.Fertilization in the human beings is internal and takes place in the proximal part of fallopian tube of the female. Fertilization involves following processes :

1. Approach of sperm to ovum:

During the copulation, male inserts its erectile penis in the vagina of female and releases about 3.5 ml of seminal fluid. This process is called ejaculation. Seminal fluid contains as many as 400 million sperms.This ensures the reaching of number of sperms.This ensures the reaching of a number sperms to the ovum as many sperms are killed by the acidity of female genital tract and many sperms are engulfed by the phagocytes of the vaginal epithelium so that only about 100 sperms reach the fallopian tube. The sperms swim in the seminal fluid by lashing movements of their tail at the rate of 1-4 mm per minute.The sperms swim towards the fallopian action of the uterus and peristaltic movements of the fallopian tube. Capacitation is the phenomenon of physiological maturation of sperms inside the female genital tract. It occurs in the presence of viscous fluid secreted from the secretory cells of epithelial lining of oviducal mucosa.It takes about 5-6 hours.
Ovum is released from the graafian follicle of ovary on the 15th day of menstrual cycle and the process is called ovulation (the expulsion of an ovum from the ovary). Ovum is trapped by the fimbrae of the ampulla of fallopian tube. Ovum moves in the tube towardsthe uterus by peristalsis and ciliary action. At the time of ovulation,egg is at secondary oocyte stage.
Fertilizability and viability of gametes are limited varying from few minutes to a few hours or days. The fertilizability of human sperms in the female genital tract is of 12 to 24 hours while its survival value is 3 days.Secondly the ovum is non motile and the energy contents of sperm must approach the egg as quickly as possible. Fertilizability period of ovum is only 24 hours though it can live for 72 hours.

2. Penetration of sperms:

Secretions of seminal vesicles,prostate gland and cowper's gland form the major part of seminal fluid. These secretion activate the sperms in fertilizing the egg and neutralise the acidity if vagina.
The sperm generally comes in contact with ovum in the animal pole while the opposite of the ovum is called as vegetal pole.Ovulation in  the human female occurs at secondary oocyte stage in which meiosis-I has been completed and first polar body has been released but second maturation is yet to complete. Penetration of sperm is chemical mechanism. In this acrosome of sperm undergoes acrosomal reaction and release certain sperm lysins which dissolves the egg envelopes locally and make the path for penetration of the sperm. Sperm lysins are acidic proteins.

3. Cortical reaction:

The penetration of sperm into the egg initiates a series of processes like:
Cortical granules appear in the egg cortex. The vitelline membrane starts lifting the cortical surface of the egg. The produces a perivitelline space within the vitelline membrane.Cortical granules are extruded in the peri vitelline space by exocytosis and some of these are attached along inner surface of the vitelline membrane which now thickens and becomes imperviuos to many other sperm entry. It is now called fertilization mambrane. It prevents the polyspermy.
4. Fusion of gametic nuclei:
The sperm entry stimulates the stimulates the secondary oocyte to undergo meiotic II division which produces ovum and second polar body.Inside the ovum,sperm nucleus takes definite path called copulation path. The centrioles of the middle piece of the sperm form a spindle. The nuclear membrane of the gametic nuclei degenerates and two sets of chromosomes initially lie on two poles of the spindle but later these sets of chromosome mix up and the process called ''amphimixis''. The fertilized egg is now called zygote while the zygote nucleus is called synkaryon.

Embryonic development

Embryonic development (Embryogenesis) includes a definite series of phases which are fundamentally similar in all sexually reproducing organisms,and transform one-celled zygote to a multicellular and fully formed developmental stage till hatching or birth. Such a remarkable similarity of embryonic development proves that all metazoans are interrelated and have common ancestory.

Phases of Embryonic Development

Embryonic development involves five dynamic changes and identifiable processes:

1. Gametogenesis : 

Gametogenesis is of two types 
(a) Spermatogenesis- formation of sperms.
(b) Oogenesis- formation of ova.

2.Fertilization:

Menstrual (Ovarian) cycle

Reproductive period of human female(about 30 to 33 yrs)extends from puberty(10-14 yrs) to menopause(45-55 years).During this reproductive period,ovaries and female reproductive tract undergo a series of cyclic changes which are primarily meant to prepare them for fertilization and pregnancy and collectively form the menstrual cycle.Most peculiar feature of this cycle is the periodic vaginal bleeding called menstruation which lasts for about four days.
Period: The lenght of menstrual cycle varies widely in women,but on average it is completed in 28 days .In a female ,successive cycles may vary in lenght by 1 to 2 days.It is absent during pregnancy,may be suppressed during lactation and permanently stops at menopause.
Phase: Menstrual cycle is divided into four phases:

1.Follicular or post-menstrual or pre-ovulatory phase.It follows  the menstrual phase and lasts for about 10 12 days(5th to14th day of menstrual cycle).It involves following changes:
(a) Under the stimulation of FSH-RF of hypothalamus,there is increased secretion of FSH from anterior pituitary.
(b) FSH stimulates the change of a primary follicle of the ovary into graafian follicle.
(c) Follicular cells of Graafian follicle secrete estrogens.

2.Ovulaotry phase: It involves the ovulation from the Graafian follicle of ovary.It occurs midway between two menstrual cycles on the 15th day of the onset of the menstrual cycle.It is caused by increasing turgidity and contraction of smooth muscle fibres around the Graafian follicle. Ovum is received by the fimbrae of the Fallopian tube. Ovum is viable for two days. Ovulation is controlled by the increased level of LH also starts the change of empty Graafian follicle into corpus luteum and secretion of progesterone from corpus.

3.Luteal or Progestational or Pre-menstrual or Secretory phase or Post-ovulatory phase:
It lasts for about 12-14 days and extends from 16th to 28th day of the menstrual cycle.It is characterised by following changes:
(a) Corpus luteum(yellow body) formed from empty Graafian follicle,increases in size,so is called luteul phase.
(b) Corpus luteum secretes progesterone hormone whose level in blood gradually increases.

4.Menstrual phase: It lasts for about 3-5 days and extends from 1st to 4th day of the menstrual cycle.When the ovum remains unfertilized,then the corpus luteum starts degenerating.The level of progesterone in the blood declines.The uterine tissues fail to be maintained. Then the unfertilized ovum along with ruptured uterine epithelium,about 50-100 ml of blood and some mucus is discharged out through the vaginal orifice and is called menstrual flow or menstruation.

Decrease in the level of progesterone and estrogens in the blood stimulates the hypothalamus and the anterior pituitary to release FSH-RF and FSH respectively. FSH starts the follicular phase of next menstrual cycle.
However, if  fertilization occurs then blastula undergoes implantation and a chorionic placenta is formed between the foetus and the mother. Placenta secretes Human Chorionic Gonadotrophin (HCG) which maintains the corpus luteum and the progesterone secretion continues. Progesterone maintains pregnancy and prevents ovulation during gestation period.

ORGANS FROM ECTODERM:

The ectoderm gives rise to the outer layer of the skin over the entire surface of the embryo.
The neural tube into which the medullary groove develops loses its original connection with the surface.Anteriorly it becomes enlarged and forms the brain,the remaining portions developing in to the spinal cord.The thickening of the walls of the spinal tube, which forms the cord,diminishes the central cavity,until it becomes reduced to a fine canal Canalis centralis.
The anterior portion of the tube becomes divided by slight constriction into forebrain ,midbrain, and hindbrain.
Hind brain becomes widened from side to side especially infront its flair and the sides thicken which develops into cerebellum,which remains thin and membranous and becomes thrown into series of folds which support a mass of blood vessels, called choroid plexus.
The portion of the hindbrain which does not form cerebellum is converted into medulla.The midbrain grows out dorsally and laterally into a pair of hollow processes called optic lobes.
The forebrain soon becomes separated into 2 parts, the Thalamencephalon behind and the cerebral hemisphere which grow out from the latter in front hollow out growth- the infundibulum ,which extends downwards.
The sides of thalamencephalon give rise to optic vesicles,which grow out until they come in close contact with the surface ectoderm.
The distal end of the vesicles widens cut and forms Retina of eyes stalk giving rise to the optic nerve.
The lining of the mouth cavity is formed from an invagination of ectoderm-the stomoderm and similar ectodermal invagination Proctoderm forms the lining of a small part of the post end of the alimentary canal.
 The lens,cornea,retina of eye,vesicle of inner ear also take thin origin from this layer.

ORGANS FROM ENDODERM:

Endoderm forms the lining of the alimentary canal and lining of all organs,which arise as outgrowths from it.It forms liver which at the beginning appear as an out pocketing of the ventral side near anterior end.It becomes folded and branched to form number of clusters of tubules, all emptying into into a common canal -the bile duct. A lateral  outgrowth of the bile duct forms the gall bladder forms the gall bladder. The pancreas arises in the same way as the liver, but as a pair of outgrowths instead of one,but they form a single organ and their ducts later become connected with the bile duct.

Bladder arises as an outgrowth of ventral side of the alimentary canal. Lungs appear as a pair of pouches from the sides of aesophagus. The Gill slits in the frog appear in the form of five solid outgrowths on each side of the anterior portion of archenteron.

 Frog Embryology

Fertilization in case of frog takes place by the process of pseudocopulation because there is no external copulatory organ present in case of male and the female are in close proximity during the process it has the name pseudocopulation.

The egg gets surrounded by many sperms and there is specific reaction called as fertilizin-antifertilizin reaction between the two.(Fertilizin is present in the jelly layer of the egg and anti-fertilizin is secreted by the acrosome of the sperm).The sperm traces its path through the jelly layer and gets attached to the vitelline membrane.
The next reaction which takes place is acrosomal reaction followed by cortical action after which the vitelline envelope is converted into thick fertilization membrane.This prevents polyspermy.As soon as the sperm enters the ova(i.e.,the nucleus of sperm enters the egg) the second meiotic division is completed resulting in the release of the second polar body.
The space between the fertilization membrane and PM of the egg is called as peristelline space which is filled with the perivitelline fluid. In this fluid,the egg can rotate freely and also this space allows free exchange of gases.


The egg pronucleus and the female pronucleus fuse together to form the zygotic nucleus,this process is known as Amphimixis or Syngamy.
The entry of the sperm causes formation of a Grey crescent (which is a characteristic of an amphibian embryo);caused due to mixing of cytoplasmic granules or in other words due to the cytoplasmic movement because of the sperm entry.Grey crescent materials the functions as an organizer because if it is removed from the embryo,the embryo fail to develop further. At the same time if a normal embryo is grafted with another Gery crescent then two embryos develop.

Thus,formation of grey crescent fixes up final symmetry of the egg and future embryo.Also grey crescent marks the future dorsal side of the embryo.The sperm penetrates the egg perpendicular to the cortex and after penetration moves perpendicularly along the radius of the egg.This path of sperm in the egg cortex, is called as penetration path.After crossing the cortex,the sperm changes its direction and moves towards the egg nucleus.This changed path is also copulation path because it leads to the copulation (fusion) of the sperm pronuclei.
After fusion of both male and female pronuclei, a zygote nucleus is formed i.e.,a zygote will be formed
Further development of zygote proceeds with its cleavage and formation of blastula,gastrula and so on

STRUCTURE OF SPERMATOZOA:

        Mature spermatozoa of a frog is made up of 3 parts i.e., head,middle piece and tail.Middle piece region is very small as compared to that of the other sperms,The head consists of acrosome and large nucleus. The acrosome secretes enzymes which helps in penetration into the egg. The middle piece of spermatozoon is composed of almost entirely of mitochondria and centriole(Centriole helps in the spindle formation during cleavage).The mitochondrial apparatus supplies the required amount of energy  in the form of ATP.The tail of sperm is flagellar and very long.It helps in locomotion and thus is very essential for the mobility of the sperm.


1.Plasma membrane
2. Outer acrosomal membrane
3.Acrosome
4. Inner acrosomal membrane
5. Nucleus
6. Proximal centriole
7. Rest of the distal centriole
8. Thick outer longitudinal fibers
9. Mitochondrion
10. Axoneme
11. Anulus
12 . Ring fibers

A.Head
B. Neck
C.Mid piece
D. Principal piece
E. Endpiece

STRUCTURE OF OVUM

The egg of frog is spherical in shape and about 2mm in diameter.It is surrounded by three membranes viz.,outer jelly coat,middle vitelline membrane and inner plasma mambrane.
The jelly coat is formed of albumin and vitelline membrane is made up of mucopolysaccharide. The egg cytoplasm (ooplasm) has 2 regions.viz.,peripheral cortex and central endoplasm.

The cortex is granular .It shows presence of cortical granules and dark brown pigment granules.Cortical granules are arranged in a layer close to the plasma membrane. The endoplasm contains numerous plate like structures called as yolk platelets.
The egg shows well-marked polarity.On one side is the animal pole containing nucleus. The polar bodies also containing nucleus. The polar body also occupy region near animal pole whereas vegetal pole containing nucleus. The polar bodies also occupy region near animal pole whereas vegetal pole containing yolk granules the animal pole appears darker whereas vegetal pole is yellowish or whitish(lighter) in colour. As the egg contains large amount of yolk it is also called as megalecithal.
As the yolk platelets are highly concentrated at one end,polarity is distinct and hence the egg is called as Telolecithal egg.
The shell is absent.Hence the egg is non-cleidoic egg.

Oogenesis in Frogs:

Oogenesis is the process of formation of oogonia and its development into mature ova.Oogenesis takes place inside the ovary of a female frog.
The ovary epithelium cells are the primordial germ cells which multiply in number to form oogonia.Oogonia further give rise to follicle cells and the primary oocyte.Cells which fail to undergo repetetive mitotic divisions
become follicular cells.
There is no way to determine which oogonium is to be selected for the formation of primary oocyte or which is to become a follicular cell.
The different stages of maturation of oogonium are primary oocyte,secondary oocyte,mature oocyte and fertilized oocyte(ovum)
The development requires 3 stages seasons during which the oogonia passes through 3 phases i.e., Multiplication phase,Growth phase and Retention phase.

MULTIPLICATION PHASE:

This phase of ova starts right from the tadpole stage of the organism and exists upto the older stage i.e., adult stage.During this time the oogonium enters mitosis to form primary oocyte.The primary then enters the prophase I  of meiosis I and before completion of this division it enters into the growth phase.

GROWTH PHASE:

In this phase the primary oocyte increases tremendously in size.The volume of nuclear sap increases therefore the nucleus becomes inflated and is called as Germinal vesicle.The volume of cytoplasm of oocyte also increases qualitatively and quantitatively.Amount of yolk platelets and glycogen etc increases with tremendous rate and a definite polarity is determined.Yolk tends to accumulate at one pole,i.e.,vegetative pole and occupies 2/3rd space of egg.Germinal vesicle is pushed and move towards the animal pole which is comparatively yolk free.This process of yolk formation is also known as vitellogenesis.
There is formation of vitelline membrane around the egg plasma membrane the primary oocyte reach then full growth towards the end of the second season but they are not immediately released.

RETENTION PHASE:

In this phase,the primary oocyte in the ovary are retained until the next breeding season. The 1st maturation division occurs at the time of ovulation.It forms secondary oocyte haploid and the first polar body. These changes occur as the egg leaves the ovary and before it reaches th oviduct. When the egg reaches the oviduct, the second maturation division begins.Spindle of meiosis II is formed and it progresses as far as early stage of metaphase.Again the growth is arrested until and unless the ovum is fertilized.
There may be division of 1st polar body to give rise to two polar bodies therefore there may be 2-3 polar bodies attached to the egg surface.After this the egg(female)pronucleas and male pronucleus fuse together to form zygote nucleus which is diploid in nature.
As soon as the sperm touches the vitelline envelope of the egg, the metaphase is completed and there is a formation of matured ovum and the 2nd polar body.

What does an Allergy means?

An allergy refers to an exaggerated reaction by our immune system in response to bodily contact with certain foreign substances. It is exaggerated because these foreign substances are usually seen by the body as harmless and no response occurs in non- allergic people. Allergic people's bodies recognize the foreign substance and one part of the immune system is turned on. Allergy-producing substances are called "allergens." Examples of allergens include pollens, dust mite, molds,danders, and foods. To understand the language of allergy it is important to remember that allergens are substances that are foreign to the body and can cause an allergic reaction in certain people.
When an allergen comes in contact with the body, it causes the immune system to develop an allergic reaction in persons who are allergic to it. When you inappropriately react to allergens that are normally harmless to other people, you are having an allergic reaction and can be referred to as allergic or atopic. Therefore, people who are prone to allergies are said to be allergic or "atopic."
An over-reactive immune system is involved in allergy.  Most people think that their immune system is weak when allergies strike, and they choose immune enhancing herbs or supplements.  In some cases this is true, but for most people the approach needs to be broad based, in the direction of soothing over-reactive cells.  

 Improving Immunity

                Your immune system has the ability to respond to diseases of all kinds. This is dependent on many complex reactions between the components of your immune system and the antigens on the disease causing agents. Your immune system can recognize invading substances, it can mount a specific attack on each invader as an individual, and it can remember that particular invader so that it can mount a secondary disease preventing attack upon later exposures.
 Your immune system is still the best weapon to fight a viral infection. It doesn't matter if it is a new virus like Avian Flu (H5N1), Severe Acute Respiratory Syndrome (SARS), West Nile Virus, or the common cold. If it's a virus, your immune system will try to kill it.
Your immune system's ability to protect your body is both instinctive and learned - in other words, it informs your body's actions with both innate and acquired responses. Each individual is born with innate immunity - the ability of your immune system to recognize what doesn't belong in the body. Along with passive defenses like skin, (your first line of defense), stomach acid and mucus, the innate immune system also contains active immune response mechanisms that include Natural Killer, or NK cells. Like all innate front line defense agents, NK cells do not need prior exposure in order to act. They simply recognize foreign cells and go to work.

Eat more black currants, green leafy vegetables red peppers and citrus fruits. All are good sources of vitamin C which boosts immune defences. Alternatively, supplement your diet with a daily dose of vitamin C. If you suffer from indigestion when taking vitamin C, a non-acid version, known as ester-C may be more easily absorbable.

A powerful antiviral, antioxidant and immune-boosting herb from the Peruvian rain forest, Cat’s Claw contains substances called alkaloids, which research has shown help fight infection. You can drink it in a tea (one cup a day should be enough for general maintenance) or in capsule (click here to order)

According to research a good old laugh triggers the release of the antibody immunoglobulin into the blood stream while the number of white T-cells also increases, both of which increase immunity. Watch a comedy on TV or rent a funny video. And as laughter is infectious sharing your jokes with your friends and family could help to keep them in the pink as well.
Regular light-to-moderate activity such as a daily 30-minute walk or swim in your local pool helps circulate the white blood cells around the body and tones up the cardiovascular system which in turn helps to strengthen your immune system.

Get your nightly sleep quota and you immediately increase your chances of warding off infection. Try to stick to a regular routine of wake up and and bed time to set your biological clock.
This popular herb has been shown to be more powerfully antibiotic than penicillin and tetracycline. It contains more than 200 compounds including allicin and sulphur – a strong free radical scavenger with super antioxidant properties. Eat garlic raw if possible as cooking destroys the chief active ingredient allicin. Try it sprinkled over salads or if you can’t bear the taste or smell, in an odourless capsule form.

Keep in regular contact with your friends as much as possible; studies show that positive feelings such as joy and love can boost your wellbeing significantly – so much so that people with a busy social life have been found to be four times less likely to catch a cold. Hugs and kisses can also boost physical and mental wellbeing, helping your body heal itself and fight off bugs and viruses.

Stressful moments have a direct effect on the immune system with many studies showing that constant daily pressure quickly reduces your resistance to a virus or disease. Relaxation techniques such as acupuncture, massage and even a relaxing hobby can all help to keep you calm. The gentle movements of Chi kung or T’ai Chi are also particularly effective against anxiety and stress.

Commonly known as the purple coneflower, this wonder herb contains active ingredients in its roots and leaves that have ant-viral, antibiotic and anti-inflammatory properties. It is thought to help encourage the production of white blood cells and helps speed them along to infected areas. As a result it can help shorten or prevent the course of an acute infection and stop colds or flu developing into more serious conditions such as sinusitis, bronchitis or middle ear infections. 

 Probiotic supplements encourage the growth of friendly bacteria in the body, which help to keep disease-causing organisms at bay. Research has found that if you eat a low-fat Bio yoghurt every day, you're 25 per cent less likely to develop a cold than non-yoghurt eaters - and if you do get a cold, symptoms disappear more quickly. It's thought that the live bacteria in the yoghurt provide protection by producing natural antiviral substances in the body.

The above overview of innate and adptive immunity depicts a miuticomponent interactive system that protects the host from infectious diseases and from cancer.This overview would not be complete without mentioning that the immune system can function improperly.Sometimes the immune system fails to protect the host adequately or misdirect its activities to cause discomfort common manifestations of immune dysfunction:


* Allergy and asthma
* Graft rejection and graft-versus-host disease
* Autoimmune disease
* Immunodeficiency

Allergy and asthma are results of inappropriate immune responses,often to common antigens such as plant pollen,food,or animal dander.The possibility that certain substances increased sensitivity rather than protection was recognized in about 1902 by Charles Richet,who attempted to immunize dogs against the toxins of a type of jellyfish,physalia.He and his colleague Paul Portier observed that instantly,and fatally,to subsequent challenge with minute amounts of the toxin.Richet concluded that a succesful immunization or vaccination results in phylaxis,or protection,and that an opposite result may occur- anaphylaxis-in which exposure to antigen can result in a potentially  lethal sensitivity to the antigen if the exposure is repeated.Richet recieved the Nobel Prize in 1913 for his discovery of the anaphylactic response.
Fortunately,most allergic reactions in humans are not rapidly fatal.A specific allergic or anaphylactic response usually involves one antibody type,called IgE.Binding of IgE to its specific antigen (allergen) releases substances that cause irritation and inflamation.When an allergic individual is exposed to an allergen,symptoms may include sneezing,wheezing,and difficulty in breathing(asthma);dermatitis or skin eruptions(hives);and,in more extreme cases,strangulation due to blockage of airways by inflammation.A significant fraction of our health resources is expended to care for those suffering from allergy and asthma.The frequency of allergy and asthma in the United States place these complaints among the most common reason for a visit to doctor's office or to the hospital emergency room.
When the immune system encounters foreign cells or tissue,it responds strongly to rid the host of the invaders.However,in some cases,the transplantation of cells or an organ from another individual,although viewed by the immune system as a foreign invasion,may be the only possible treatment for disease.For example,it is estimated that more than 60,000 persons in the United States alone could benefit from a kidney transplant.Because the immune ayatem will attack and reject any transplanted organ that it does not recognize as self,it is a serious barrier to this potentially life-saving treatment.An additional danger in transplantation is that any transplanted cells with immune function may view the new host as nonself and react against it.This reaction,which is termed graft-versus-host-disease, can be fatal.The rejection reaction and graft -versus-host disease can be suppressed by drugs,but this type of treatment suppresses all immune functions,so that the host is no longer protected by its immune system and becomes susceptible to infectiuuos diseases.Transplantation studies have played a major role in the develpoment of immunology..
In certain individuals,the immune system malfunctions by losing its sense of self and nonself,which permits an immune attack upon the host .This condition, autoimmunity, can cause a number of chronic debilitating diseases.The symptoms of autoimmunity differ depending on which tissues and organs are under attack.

               The field of immunology is concerned mostly with how innate and adaptive mechanisms collaborate to protect vertebrates from infection.Although many cellular and molecular actors have important roles,antibodies and lymphocytes are considered to be the principal players .Yet despite their prominence in vertebrate immune systems,it would be a mistake to conclude that these extraordinary molecules and versatile cells are essential for immunity.In fact, determinants search for antibodies,T cells,and B cells in organisms of the non vertebrate phyla has failed to find them.The interior spaces of organisms as diverse as fruit flies,cockroaches,and plants do not contain unchecked microbial populations,however,which implies that some sort of immunity exists in most,possibly all,multicellular organisms,including those with no components of adaptive immunity.
            A major difference between adaptive and innate immunity is the rapidity of the innate immune response,which utilizes a pre-existing but limited repertoire of responding components.Adaptive immunity compensates for its slower components.Adaptive immunity compensates for its slower onset by its ability to recognize a much wider repertoire of foreign substances,and also by its ability to improve during a response,whereas innate immunity remains constant.It may also be noted that secondary adaptive responses are considerably faster than primary responses.Principle characteristics of the innate and adaptive immune systems.
            Insects and plants provide particularly clear and dramatic examples of innate immunity that is not based on lymphocytes.The invasion of the interior body cavity of the fruit fly ,Drosophila melanogaster,by bacteria or molds triggers the synthesis of small peptides that have strong antibacterial or anti-fungal activity.The effectiveness of these antimicrobial peptides is demonstrated by the fate of mutants that are unable to produce them.For example,a fungal infection overwhelms a mutant fruit fly that is unable to trigger the synthesis of drosmycin, an antifungal peptide.Further evidence for immunity in the fruit fly is given by the recent findings that cell receptors recognizing various clases of microbial molecules were first found in Drosophila.
                 Plants respond to infection by producing a wide variety of antimicrobial proteins and peptides,as well as small nonpeptide organic molecules that have antibiotic activity.Among these agents are enzymes that digest microbial cell walls,peptides and a protein that damages microbial membranes,and the small organic molecules phytoalexins.The importance of the phytoalexinsis shown by the fact that mutations that alter their biosynthetic pathways result in loss of resistance to many plant pathogens goes beyond this chemical assault to include in the infected area  by strengthening the walls of surrounding cells.

         Since antibodies are glycoproteins,they can themselves function as potent immunogens to induce an antibody response.Such anti-Ig antibodies are powerful tools for the study of B-cell development and humoral immune responses.The antigenic determinants,or epitopes,on immunoglobulin molecules fall into three major categories:isotypic,allotypic,and idiotypic determinants,which are located in characteristic portions of the molecule.
         Isotype determinants are consonant-region determinants that collectively define each heavy-chain class and sub class and each light-chain type and subtype within a species.Each isotype is encoded by a separate consonant region gene,and all members of a species carry the same consonant-region genes(which may include multiple alleles).Within a species,each normal individual will express all isotypes.Therefore,when an antibody from one species,each normal individual will express all isotypes in the serum.Different species inherit different constant-region genes and therefore express different isotypes.Therefore,when an antibody from one species is injected into another species,the isotypic determinants will be recognized as foriegn,inducing an antibody response to the isotypic determinants on the foriegn antibody.Anti-isotype antibody is routinely used for research purposes to determine the class or subclass of serum antibody produced during an immune response or to characterize the class of membrane-bound antibody present on B cells.
Allotype:   
           Although all members of a species inherit the same set of isotype genes,multiple alleles exist for some of the genes.These alleles encode subtle amino acid differences,called allotypic determinants displayed by an antibody determines its allotypes.In humans,allotypes have been characterized for all IgG subclasses,for one IgA subclass,and for the light chain.The gamma chain allotypes are referred to as Gm markers.At least 25 different Gm allotypes have been identified;they are designated by the class and subclass followed by the allele number,for example,G1m(1),G2m(23),G3m(11),G4m(4a). Of the two IgA subclasses,only the IgA2 subclass has allotypes,as A2m(1) andA2m(2). The light chain has three allotypes.Each of these  allotypic determinants represents differences in one to four amino acids that are encoded by different alleles.
         The unique amino acid sequence of the Heavy and light domains of a given antibody can function not only as an antigen-binding site but also as a set of antigenic determinants.The idiotypic determinants arise from the sequence of the heavy and light chain variable regions.Each individual antigenic determinant of the variable region is referred to as an idiotope.In some cases an idiotope maybe the actual antigen-binding site,and in some cases an idiotope may comprise variable region sequences outside of the antigen-binding site.Each antibody will present multiple idiotopes;the sum of the individual idiotopes is called idiotype of the antibody.
Because the antibodies produced by individual B cells derived from the clone have identical variable-region sequences,they all have the same idiotype.Anti-idiotype antibody is produced by injecting antibodies that have minimal variation in their isotypes and allotypes ,so that the idiotypic differences can be recognized.Often a homogenous antibody such as myeloma protein or monoclonal antibody is used.Injection of such an antibody into a recipient who is genetically identical to the donor will result in formation of anti-idiotype antibody to the idiotypic determinants.

The factors that promotes Oxygen binding as well as Oxygen dissociation with respect to Hb are as follows:                                                                                                                                                   

            The heme prosthetic group associated with each chain is held in position by a coordinate covalent bond between the ion atom and a nitrogen atom in the side chain of His residue.The 4 heme groups serve as the sites for Oxygen binding.Hence each Hb molecule is able to bind reversibly with four molecule of Oxygen.The heme 'Fe' must be maintained in the ferrous state because Ferric ion is unable to bind to Oxygen.

3D Structure of Hemoglobin.

                       Binding of Oxygen with Hb follows a 'binding pattern' called cooperative binding which results from changes in hemoglobin 3D structure  that are initiative when the 1st Oxygen binds.The binding of 1st Oxygen molecule facilitates binding of remaining 3 Oxygen molecules
When the 1 st Oxygen molecule binds to a particular heme site,a message is communicated via conformational changes in the protein chains to the other heme sites.This subtle conformational changes as Allosteric interactions.
             The Hb molecules as far as structural  conformation is concerned is often referred as oxygenated Hb in R or relaxed state while deoxygenated Hb in T or taut state.
Hb alternates between these 2 stable conformations namely R and T states.In the lungs where Oxygen tension is high Hb gets quickly saturated and as a result gets coverted into 'R' state.
             In the tissues where Oxygen tension is low Hb becomes unsaturated and gets converted into 'T' state.
             The co-operative binding of Oxygen to Hb is influenced by Carbon dioxide and hydrogen ions.This observation was made by the biochemist Christian Bohr and therefore called 'Bohr effect'. Carbon dioxide and hydrogen ions bind to Hb molecule causing changes in its quaternary structure that stabilise deoxygenated form and destabilise oxygenated form.This binding process reduces affinity of Oxygen for Hb and enhances release of Oxygen for Hb.The action of carbondioxide and hydrogen ions are caused by allosteric effect i.e., carbondioxide and hydrogen bind to Hb causing subtle conformational changes throughout the Hb structure thereby influencing Oxygen affinity at the heme site.                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

         WBC are far less numerous than RBCc averaging from 5,000-10,000 per cubicmm of blood.The ratio of RBCs to WBCs is around 700:1. The term leucocytosis refers to increase in the number of WBCs.The term Leucopenia refers to an abnormally low levels of WBCs(below 5000 per cubic mm). The term Leukemia refers to a very abnormal increase in specific type of WBC.


         Since bacteria exist everywhere in the environment and have easy continuous acces to the body especially through mouth,nose and skin pores. Many cells especially the cells of Epithelial tissue are subjected to aging and death and their remains must be disposed off by phagocytes that actively injest bacteria and debris.In a healthy body some WBCs especially lymphocytes can live for several months or even years but on an average there is no fixed life span for WBCs.Life span is decided by the period of infection e.g.,During severe infection phagocytic WBCs may live or survive only for a few hours.

Antigen-Antibody Interactions: Strength or Antigen-Antibody Interactions.
         The noncovalent interactions that form the basis of antigen-antibody(Ag-Ab)binding include hydrogen bonds,ionic bonds,hydrophobic interactions,and van der waals interactions.Because these interactions are individually weak(compared with a covalent bond),a large number of such interactions are required to form a strong Ag-Ab interactions.Furthermore,each of these noncovalent interactions operates over a very short distance,generally about 1 angstorms;consequently,a strong Ag-Ab interaction depends on a very close fit between the antigen and antibody.Such fits require a high degree of complementarity between antigen and antibody,a requirement that underlies the exquisite specificity that characterizes antigen-antibody interactions.

        The combined strength of a noncovalent interactions between a single antigen-binding site on an antibody and a single epitope is the affinity of the antibody for that epitope.Low-affinity of the antibodies bind antigen weakly and tend to dissociate readily,whereas high-affinity antibodies bind antigen more tightly and remain bound longer.The association between a binding site on an antibody(Ab)with a monovalent antigen(Ag)can be described by the equation.

WBC Physiology:
             Once pathogens enter the body,the general function of WBC is to fight or combat by phagocytosis or immune responses.Neutrophils and macrophages are active in phagocytosis.Several different chemicals in the inflammed tissue attract phagocytes towards the tissue,this phenomenon is called chemotaxis.Among the substances that provide stimuli for chemotaxis are toxins produced by microbes,specialised products of damaged tissues called Kinins.


             Most Leucocytes possess the ability to squiz through walls of capillaries and this movement through walls is called Diapedes.Among the WBCs neutrophils respond tissue destruction by bacteria most quickly.After engulfing a pathogen during phagocytosis neutrophils releases several destructive chemicals such as antibacterial enzyme Lysozyme and strong oxidants like  hydrogen peroxide.Neutrophils also contain Defensins specialized proteins that exhibit a broad range of antibiotic activity against bacterial,fungi and viruses.As compared to neutrophils monocytes take a little longer to reach a site of infection but once they arrive,they arrive in large number and destroy microbes.On their arrival at a site of infection monocytes enlarge and differentiate into wandering macropahges which clean up cellular debris,following the infection Eosinophils are believed to release enzymes such as histaminase that combats the effects of Histamine is allergic reactions.Eosinophils are most effective against parasitic worms a high high eosinophil count often indicates prarsitic infection.Basophils are also involved in inflammatory and allergic reactions.They develop into mast cells which liberate chemicals like Histamine,Heparin and Serotonin.These substances intensify inflammatory reactions and are involved in hypersnsitivity or allergic reactions.

       Unlike R.B.C.s leucocytes of W.B.C. have a well defined nucleus and do not contain hemoglobin.The two major groups of W.B.C.s are granular W.B.C.s and Agranular W.B.C.s.,

Types of WBCs

Granular Leucocytes:-
      Also called as granulocytes showing lobed nuclei and conspicuous granules in the cytolasm.These are of three types viz.,Neutrophils,Eosinophils and Basophils.These name reflect the types of granules seen when using hematology stain Giemsa stain or Leishman's stain.But the most preferred stain is Wright's stain which include both acidic Eosin and Basic dye.The nuclei of Neutrophils may have 2-6 lobes connected by very thin strands as the cells age the extent of nuclear lobulation increases.Because the older Neutrophils appear to have many differently shaped nuclei they are often called as polymorphonuclear leucocyte or simply polymorphs.The younger neutrophils are often called as bands because their nucleus id rod shaped.The cytoplasm of neutrophils shows fine lilac colored granules.The nucleus of an Eosinophils usually has two lobes connected by a thin or thick strand.The granules in the cytoplasm are large and they stain reddish orange.The nucleus of a basophils is irregular often in the form of letter 'S'.The granules in their cytoplasm are variable in size and stain bluish black.

Agranular Luecocytes:-
       Also called Agranulocytes whereby no cytoplasmic granules can be seen.The two kinds of Agranulocytes or Lymphocytes and Monocytes.The nuclei of Lymphocytes are darkly stained,roundish showing slightly indented shape.The cytoplasm stains sky blue.The nuclei of monocytes are kidney shaped and the cytoplasm has blurred appearance.Some of them reside in a particular tissue and are referred as fixed macrophages.E.g., macrophages are wandering or free macrophages which roam and gather at sites of infection or inflamation.Just like RBCs have surface(Major Histo Compatibility antigen)(these are contains for each person).

                The binding of an antibody to its antigen is similar in many ways to the binding involves weak,non covalent interactions and exhibits high affinity.What distinguishes an antibody-antigen interaction is that the antibody does not alter the antigen,whereas the enzyme catalyzes a chemical change in its substrate.However,like enzymes,antibodies of appropriate specificity can stabilize the transition state of a bound substrate,thus reducing the activation energy for chemical modification of the substrate.
               The similarities between antigen-antibody interactions and enzymes-substrate interactions raised the question of whether some antibodies could behave like enzymes and catalyze chemical reactions.To investigate this possibility,a hapten-carrier complex was synthesized in which the hapten structurally resembled the transition state of an ester undergoing hydrolysis.Spleen cells from mice immunized with this transition state analogue were fused with myeloma cells to generate monoclonal antihapten monoclonal antibodies.When these monoclonal antibodies were incubated with an ester substrate,some of them accelarated hydrolysis by about 1000-fold;that is,they acted like the enzyme that normally catalyzes the substrate's hydrolysis.This catalytic activity of these antibodies was highly specific;that is,they hydrolized only esters whose transition-state structure closely resembled the transition state analogous used as hapten in the immunizing in reference to their dual role as antibody and enzyme.
              A central goal of catalytic antibody research is the derivation of a battery of abzymes that cut peptide bonds at specific sites.Such abzymes would be invaluable tools in the structural and functional analysis of proteins.Additionally,it may be possible to generate abzymes with the ability to dissolve blood clots or to cleave viral glyco[roteins at specific sites,thus blocking viral infectivity.Unfortunately,catalytic antibodies that cleave the peptide bonds of proteins have been exceedingly difficult to derive.Much of the research currently being pursued in this field is devoted to the solution of this important but difficult problem.

                Monoclonal antibodies are proving to be very useful as diagnostic,imaging,and therapeutic reagents in clinical medicine.Initially,monoclonal antibodies were primarily as in vitro diagnostic reagents.Among the many monoclonal antibody diagnostic reagents now available are products for detecting pregnancy,diagnosing numerous pathogenic microorganisms,measuring the blood levels of various drugs,matching histo compatibility antigens, and detecting antigens shed by certain tumors.
                Radiolabeled monoclonal antibodies can also be used in vivo for detecting or locating tumor antigens,permitting earlier diagnosis of some primary or metastatic tumors in patients.For example,monoclonal antibody to breast-cancer cells is labeled with iodine-131 and introduced into the blood to detect the spread of tumor to regional lymph nodes.This monoclonal imaging technique can reveal breast-cancer metastates that would be undetected by other,less sensitive scanning techniques.
Immunotoxins composed of tumor-specific monoclonal antibodies coupled to lethal toxins are potentially valuable therapuetic reagents.The toxins used in preparing immunotoxins include ricin,shigella toxin,and diphtheria toxin,all that s single molecule has been shown to kill a cell.Each of these toxins consists of two types of functionally distinct polypeptide comonents,an inhibitory(toxin)chain and one or more binding chains,which interact with receptors on cell surfaces;without the binding polypeptide(s) the toxin cannot get into cells and therefore is harmless.An immunotoxin is prepared by replacing the binding polypeptide(s) with a monoclonal antibody that is monoclonal antibody that is specific for a particular tumor cell.In theory,the attached monoclonal antibody will deliver the toxin chain sppecifically to tumor cells,where it will cause death by inhibiting protein synthesis.The initial clinical  responses to such immunotoxins in patients with leukemia,lymphoma,and some other types of cancer have shown promise,and research to develop and demonstrate their safety and effectiveness is underway.

 Monoclonal Antibody Production:
            As we have studied earlier,most antigens offer epitopes and therefore induce proliferation and differentiation of a variety of B-cell clones,each derived from a B cell that recognizes a particular epitope.The resulting serum antibodies are heterogeneous,comprising a mixture of antibodies,each specific for one epitope.Such a polyclonal antibody response facilitates the localization,phagocytes,and complement-mediated lysis of antigen;it thus has clear advantages for the organism in vivo.Unfortunately,the antibody heterogenecity that increases immune protection in vivo often reduces the efficacy of an antiserum for various in vitro uses.For most research,diagnostic, and therapeutic purposes, monoclonal antibodies,derived from a single clone and thus specific for a single epitope,are preferable.

            Direct biochemical purification of a monoclonal antibody from a polyclonal antibody preparation is not feasible. In 1975,Georges Kohler and Cesar Milstein devised  a method for preparing monoclonal antibody,which quickly became one of immunology's key technologies.By fusing a normal activated,antibody-producing B cell with a myeloma cell(a cancerous plasma cell),they were able to generate a hybrid cell,called a hybridoma,that possessed the immortal growth properties of the myeloma cell and secreted the antibody produced by the B cell.The resulting clones of hybridoma cells,which secrete large quantities of monoclonal antibody,can be cultured indefinitely.The development of techniques for producing monoclonal antibodies,gave immonologists a powerful and versatile research tool.The significance of the work by kohler and Milstein was acknowledged when each was awarded a nobel Prize.

Basic structure of antibodies: Antibodies are Heterodimers                Antibody molecules have a common structure of four peptide chains.This structure of two identical light(L)chains, polypeptides of about 25,000 molecular weight,and two identical heavy(H)chains,larger polypeptides of molecular weight 50,000 or more.Like the antibody molecules they constitute,h and L chains are also called immunoglobulins.Each light chain is bound to a heavy chain by a disulfide bond,and by such noncovalent interactions as salt linkages,hydrogen bonds,and hydrophobic bonds,to form a heterodimer(H-L)chain combinations to each other to form the basic four-chain(H-L)(H-L)antibody structure,a dimer of dimers.As we shall see,the exact number and precise positions of these interchain disulfide
 bonds differs among antibody classes and subclasses.


     The first 110 or so amino acids of the amino-terminal region of a light or heavy chain varies greatly among antibodies of different specificity.These segments of highly variable sequence are called V regions.All the differences in specificity displayed by different antibodies can be traced to differences in the amino acid sequences of V regions.In fact,most of the differences among antibodies fall within areas of the V regions called complementary-determining regions(CDRs),and it is these CDRs on both light and heavy chains,that constitute the antigen-binding site of the antibody molecule.By contrast,within the same antibody class,far fewer differences are seen when one compares sequences throughout the rest of the molecule.The regions of relatively constant sequence beyond the variable regions have been dubbed C regions.Antibodies are glycoproteins;with few exceptions,the sites of attachment for carbohydrates are restricted to the constant region.We do not completely understand the role played by glycosylation of antibodies,but it is probably increases the solubility of the molecules.Inappropriate glycosylation,or its absence,affects the rate at which antibodies are cleared from the serum,and decreases the efficiency of distraction between antibody and the complement system and between antibodies and Fc receptors.

            Blood can be separated in a centrifuge into a fluid and a cellular fraction contains red blood cells,leukocytes,and platelets.Plasma contains all soluble small molecules and macromolecules of blood,including fibrin and other proteins required for the formation of blood clots.If the blood or plasma is allowed to clot,the fluid phase that remains is called serum.It has been known since the turn of century that antibodies reside in the serum.The first evidence that antibodies were contained in particular serum protein fractions came from a classic experiment by A.Tiselius and E.A.Kabat,in 1939.

         They immunized rabbits with the protein ovalbumin(the albumin of egg white)and then divided the immunized rabbits serum intoo two aliquots.Electrophoresis of one serum aliquot revealed four peaks corresponding to albumin and alpha,beta,and gamma globulins.The other serum aliquot was reacted with ovalbumin,and the precipitate that formed was removed;the remaining serum proteins,which did not react with the antigen,were then electrophoressed.A comparison of the electrophoretic profiles of these two serum aliquots revealed that there was a significant drop in the gamma-globbulin peak in the aliquot that had been reacted with antigen.Thus,the gamma-globulin fraction was identified as containing serum antibodies,which were called immunoglobulins,to distinguish them from any other proteins that might be contained in the gamma-globulin fraction.We now know that although immunoglobulin G(IgG),the main class of antibody molecules are found in the gamma-globulin fraction,significant amounts of it and other important classes of antibody molecules are found in the alpha and the beta fractions of serum.

Antibodies of secretory IgA:- Bind to microbes in baby's digestive tract and thereby prevent their attachment to the walls of the gut and their subsequent passage into body's tissues.

B-12 binding factor:- Reduces amount of vitamin B-12,which bacteria need in order to grow.

Bifidus factor:- Promotes growth of Lactobacillus bifidus,,a harmless bacterium,in baby's gut.Growth of such nonpathogenic bacteria helps to crowd out dangerous varieties.

Fatty acids:- Disrupt membranes surrounding certain viruses and destroy them.

Fibronectin:- Increase antimicrobial activity of macrophages;helps to repair tissues that have been damaged by immune reactions in baby's gut.

Hormones and growth factors:- Stimulate baby's digestive tract to mature more quickly.Once the initially "leaky" membranes lining the gut mature,infants become less vulnerable to microorganisms.

Interferon:- Enhances antimicrobial activity of immune cells.

Lactoferrin:- Binds to iron,a mineral many bacteria need to survive.By reducing the available amount of iron,lactoferrin thwarts growth of pathogenic bacteria.

Lysozyme:- Kills bacteria by disrupting their cell walls.

Mucins:- Adhere to bacteria and viruses,thus keeping such microorganisms from attaching to mucosal surfaces.


Oligosaccharides:- Bind to microorganisms and bar them from attaching to mucosal surfaces.

SOURCE:Adapted from J.Newman,1995,How breast milk protects newborns,Sci.Am.273(6):76.

Immunoglobulin D(IgD):
IgD was first discovered when a patient developed a multiple myeloma protein failed to react with anti-isotype antisera against the then-known isotypes:IgA,IgM,and IgG.When rabbits were immunized with this myeloma protein,the resulting antisera were used used to identify the same class of antibody at low levels in normal human serum.
The new class,called IgD,has a serum concentration of 30 mu d/ml and constitute about 0.2% of the total immunoglobulin in serum.IgD,together with IgM,is the major membrane-bound immunoglobulin expressed by mature B cells,and its role in the physiology of B cells is under investigation.No biological effector function has been identified for IgD.

           The potent biological activity of IgE allowed it to be identified in serum despite its extremely low average serum concentration.IgE antibodies mediate the immediate hypersensitivity reactions that are responsible for symptoms of hay fever,asthma,hives,and anaphylactic shock.The presence of a serum component responsible for allergic reactions was first demonstrated in 1921 by K.Prausnitz and H.Kustner,who injected serum from an allergic person intra-dermally into a nonallergic individual.When the appropriate antigen was later injected at the same site,a wheal and flare reaction(analogous to hives)developed there.This reaction,called the P-K reaction(named for its originators,prausnitz and kustner),was the basis for the fiorst biological assay for IgE activity.

a) Cross-linkage by a single allergen and b) Cross-linkage by a single IgG antibody to two allergen molecules.

          Actual identification of IgE was accomplished  by K.prausnitz and T.Ishizaka in 1966.They obtained serum from an allergic individual and immunized rabbits with it to prepare anti-isotype antiserum.The rabbits antiserum was then allowed to react with each class of human antibody known at that time(i.e.,IgG,IgA,IgM,IgD).In this way,each of known anti-isotype antibodies was precipitated and removed from the rabbit anti-serum.What remained was an anti-isotype antibody specific for an unidentified class of antibody.This antibody turned out to completely block the P-K reaction.the new antibody was called IgE(in reference to the E antigen of ragweed pollen,which is a potent inducer of this class of antibody).
         IgE binds to Fc receptors on the membranes of blood basophils and tissue mast cells.Cross-linkage of receptor-bound IgE molecules by antigen(allergen)induces basophils and mast cells to translocate their granules to the plasma membrane and release their contents to the extracellular environment, aprocess known as degranulation.As a result,a variety of pharmacologically active mediators are released and give rise to allergic manifestations.Localized mast-cell degranulation induced by IgE also may release for antiparasitic defense.