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Trying to provide all necessary information about IMMUNITY and IMMUNE SYSTEM

Immune system is of two types:
1. Humoral or Antibody-Mediated Immune System(AMIS). It is formed of proteinous defensive chemicals,called antibodies,which are produced by B-lymohocytes and cieculate in the plasma of blood and lymph(humor means body fluids)and protect the body from bacteria and viruses that enter the blood and lymph.There are about100 million trillion molecules.
2. Cell-Mediated Immune System(CMIS). It is formed of highly specialized cells,called T-lymphocytes,which directly attack the pathogenic micro-organisms(like protozoans and fungal)that have entered the host's body or grafts such as transplanted kidney or skin grafts taken from another person(allografts).It also protects the body from its own cells which have become cancerous.

The Immune System Includes Innate andAdaptive Components.: 
          Immunity-the state of proctection from infectious disease-has both a less specific and more specific component,innate immunity,provides the first line of defence against infection.Most components of  innate immunity are present before the onset of infection and constitute a set of disease-resistance mechanisms that are not specific to a particular pathogen but that include cellular and molecular components that recognize classes of molecules peculiar to frequently encountered pathogens.
Innate immunity can be seen to comprise four types of defensive barriers:anatomic,physiologic,phagocytic,and inflammatory. 
The Skin and the mucosal Surfaces Provide Protective Barriers Against Infection 
Physical and anatomic barriers that tend to prevent the entry of pathogens are an organism's first line defence against infection.The skin and the surafce of mucous membrane are included in this category because they are effective barriers to the entry of most micro-organisms.The skin consists of two distinct layers: a thinner outer layer-the epidermis and a thicker layer-the dermis.The epidermis contains several layers of tightly packed epithelial cells.The outer epidermal layer consists of dead cells and is filled with a waterproofing protein called keratin.The dermis,which is composed of connective tissue,contains blood vessels,hair follicles,sebaceous glands,and sweat glands.The sebaceous glands associated with the hair follicles and produce an oily secretion called sebum.Sebum consist of lactic acid and fatty acids,which maintain the pH of the skin between 3 and 5;this pH inhibits the growth of most micro-organisms.A few bacteria that metabolise sebum live as commensals on the skin and sometimes cause cause a server form of acne.One acne drug, isotretinoin (Accutane) ,is a vitamin A derivative that prevents the formation of sebum.
Physiologic Barriers to Infection Include General Conditions and Specific Molecules
The physiologic barriers that contibute to innate immunity include temperature,pH and various soluble and cell associated molecules.Many species are not susceptible to certain diseases simply because their normal body temperature inhibits growth of the pathogens.Chickens,for example have innate immunity to anthrax because their high body temperature inhibits the growth of bacteria.Gastric acidity is an innate physiologic barrier to infection because very few ingested micro-organism can survive the low pH of the stomach contents.One reason newborn are susceptible to some diseases that do not afflict adults is that their stomach contents are less acidic than those of adults.
A variety of soluble factors contribute to innate immunity,among them the soluble proteins lysozyme, interferon,and complement .Lysozyme,a hydrolytic enzyme found in mucous secretions and in tears,is able to cleave the peptido-glycan layer of bacterial wall.Interferon comprises a group of proteins produced by virus-infected cells.
Many of the molecules involved in innate immunity have the property of pattern recognition,the ability to recognize a given class of molecules.Because there are certain types of molecules.Because there are certain types of molecules that are unique to microbes and never found in multi-cellular organisms.

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