Immunology | Immune system| Immunity

     Since World War II,penicillin has been used to successfully treat a wide variety of bacterial infections. However,the penicillin family of antibiotics is not without drawbacks.One is the role of penicillins and other antibiotics in the evolution of antibiotic resistant bacterial strains.Another is their capacity to induce allergic reactions in some patients.Penicillin and its relatives are responsible for most of the recorded allergic reactions to drugs and 97% of the deaths caused each year by drug allergies.


     Allergies to penicillin and other drugs can be induced by small doses and are not consequences of the pharmacological or physiological effects of the drugs.An allergic response usually occurs about a week or so after the patient's first exposure to the agent,with typically mild symptoms often including hives,fever,swelling of lymph nodes,and ocassionally an arthritis-like discomfort treatments with the dug usually cause much more rapid and often more severe reactions.Within minutes the throat and eyelids may swell.Grave danger arises if these symptoms progress to anaphylaxis,a physiological collapse that often involves the respiratory, circulatory, and digestive systems.Hives,vomitting,abdominal pain,and diarrhea may be a preamble to respiratory and circulatory problems that are life thraetening,Wheezing and shortness of breathmay be accompanied by swelling of the larynx and epiglottis that can be accompanied by swelling of the larynx and epiglottis that can block airflow ,and a profound drop in blood pressure causes shock,frequently accompanied by weakened heart contractions.
      The treatment of choice for anaphylaxis is injection of the drug epinephrine ,which can reverse the body's slide into deep anaphylaxis by raising blood pressure,easing constrictionof their air passages,and inhibiting the release from mast cells and basophils of the agents that induce anaphylaxis.Other drugs may be used to raise the low blood pressure,strenghen heart contractions,and expand the blocked airways.After a case of drug induced anaphylaxis,affected individuals are advised to carry a notice warning future healthcare providers of the drug allergy.

Epitope

                   Specific portions of antigen molecule trigger immune responses.These portions/regions are called as Antigenic determinants or epitopes.Most antigens have many antigenic determinants/epitopes.Each of which induces production of different type of antibody or proliferation of 'T' cells. As a rule antigenic determinants/epitopes are foreign substance and they are not usually a part of chemistry of the body. However, sometimes the immune system fails to make correct distinctions.These,then result in an auto-immune disorder in which self molecules or body's own cells are attacked as though/as if they were foreign.
             Immune cells do not interact with,or,recognize,an entire immunogen molecule; instead, lymphocytes recognize discrete sites on the the macromolecule called epitopes ,or antigenic determinants.Epitopes are the immunologically active regions of an immunogen that bind to antigen-specific membrane receptor on lymphocytes or to secreted antibodies.Studies with small antigens has revealed that B and T cells recognize different epitopes onthe same antigenic molecule.

           In 1890,Emil Behring and Shibasaburo Kitasato reported an extra-ordinary experiment.They immunized rabbits with tetanus and then collected serum from these animals.Subsequently,they injected 0.2ml of the immune serum into the abdominal cavity of six mice.After hours,they infected the treated animals and Untreated controls with live,virulent  tetanus bacteria.All of the control mice died within 48 hours of infection,whereas the treated mice not only survived but showed no effects of infection.This landmark experiment demonstrated two important points.One,it showed that following immunization,substances appeared in serum that could protect an animal against pathogens.Two,this work demonstrated that immunity could be passively acquired.Immunity could be transferred from one animal to another by taking serum from an immune animal and injecting it into a non immune one.These and subsequent experiments did not go unnoticed.Both men eventually received titles(Behring became von Behring and Kitasto became Baron Kitasto).A few years later,in 1901,Von Behring was awarded first Nobel Prize in Medicine.
           These early observations and others paved the way for the introduction of passive immunization int clinical practice.During the 1930's and 1940's, passive immuno therapy,the endowment of resistance to pathogens by transfer of the agent of immunity from an immunized donor to an unimmunized recipient,was used to prevent or modify the course of measles and hepatitis A.During subsequent years,clinical experience and advances in the technology of preparation of immunoglobin for passive immunization have made this approach a standard medical practice.Passive immunization based on the transfer of antibodies is widely used in the treatment of immunodefiency diseases and as a protection against anticipated exposure to infectious agents against which one does not have immunity.
         

       STEM-CELL transplantation holds great promise for regeneration of diseased,damaged,or defective tissue.

Human pluripotent stem cells.

          Hematopoetic cells, are already used to restore hematopoeitic cells,however ,rapid stem advances in stem-cells research have raised the possibility that other stem-cell types,too,may soon be routinely employed replacement of other cells and tissues.Two properties of stem cells underlie their utility and promise.They have capability to give rise to more differentiated cells,and they are self-renewing,because each division of stem cell creates at least one stem.If stem cells are classified according to their descent and develpomental potential,four levels of stem cells can be recognised: totipotent,pluripotent,multipotent,and unipotent.
              The transplantation of hematopoietic stem cells(HSCs)is an important therapy for patients whose hematopoeitic systems must be replaced.It has three major applications:
1. Providing a functional immune system to individuals with a genetically determined immunodeficiency,such as severe combined immunodeficiency(SCID).
 2. Replacing a defective hematopoietic system with functional one to curesome life-threatening nonmalignant genetic disorder in hematopoiesis,such as sickle-cell anemia or thalassemia.
3. Restoring the hematopoietic system of cancer patients after treatment with doses of chemotherapeutic agents and radiation so high that they destroy the system.These high-dose regimens can be much more effectve at killing tumor cellsthan are therapies that use more conventional doses of cytotoxic agents.Stem-cell transplantation makes it possible to recover from such drastic treatment.Also,certain cancers,such as some of acute myeloid luekemia,can be cured only by destroying the source of leukemia cells, the patient's own hematopoeitic system.

A type of allergy

                   Data on frequency of care sought for the most common medical complaints in United States show that asthma and allergy together resulted in more than 28 million visits to the doctor in 1995.The importance of allergy as a public health problem is underscored by the fact that the annual number of doctor visits for hypertension,routine medical examinations,or normal pregnancy,are fewer than the number of visits allergic conditions.In fact,the most common reason for a visit to a hospitalemergency room is an asthma attack counting for one third of all visits.In addition to those treated in ER,there were about 160,000 hospitalisations for asthma in the past year,with an average stay of 3 to 4 days.
                    Although all ages and races are affected,deaths from asthma are 3.5 times more common among African-American children remain unknown,although some clues may have been uncovered by recent studies of genetic factors in allergic disease.
                    An increasingly serious health problem is food allergy,especially to peanuts and tree nuts.Approximately 3 million Americans are allergic to these foods and they are leading causes of fatal and near-fatal allergic(anaphylactic)reactions.While avoidance of these foods can prevent harmful consequences,the ubiquitous use  of peanut protein and other nut products in a variety of foods makes this very difficult for the allergic individual.
                    Anaphylaxis generally occurs within an hour of ingesting the food allergen and the most effective treatment is injection of drug epinephrine.Those prone to anaphylactic attacks often carry injectable epinephrine to be used in case of exposure.
                    In addition to the suffering and anxiety caused by inappropriate immune responses or allergies to environmental antigens,there is a staggering cost in terms of lost work time for those affected and for caregivers.These costs well justify the extensive efforts by basic and clinical immunologists and allergists to relieve the suffering caused by these disorders.