IMMUNITY::
Immunity is the ability of the living body or the processes thereof to resist various types of organisms or toxins that tend to damage the tissues and organs As a first line of defence the body has many mechanisms to resist the foreign substances in the body some of these have been mentioned in the begining of the chapter this type of non-specific first line of defence to the infection present right from the birth and inherited from generations to generation is called is natural or lmmate or inherited immunity this type of immunity may vary with respect to species strains races or individuals.
Acquired Immunity::
The other type of immunity is acquired immunity this type of immunity is a specific reaction of the body to the of a foreign substance A foreign substance (e.g.bacteria viruses proteins or some drugs) which evokes such a response is called antigen it general antigens contain one or more specific chemical compounds in its makeup that are different from all other compounds of the body they are usually proteins or large polysaccharides A substance to be antigenic must have a high molecular weight 8000 or greater in certain case it may be less but here it combines with endogenous substance called haptens to become antigenic
There are two types of acquired immunity ;humoral and cell mediated in both cases lymphocytes are at work
In humoral type of immunity B- lymphocytes proliferate and differentiate into clone or plasma cells which produce antibodies or immunoglobulins these antibodies combine chemically with the specific antigen by doing so antibodies may coat bacteria enhancing their likelyhood of being phagocytosed or may combine with bacterial toxin to neutralize them on cantact with an antigen the T- lymphocytes become sensitized and on subsequent exposure to that antigen they proliferate into helper cells suppressor cells or other effector cells involved in cell medicated immunity helper cells assist B-lyphocytes to make antibodies suppressor cells and inhibit this production
In cell mediated type of immunity T-lymphocytes react directly with the foreign cells for example tissue-transplants they may also act on cells which are harbouring organisms such as tubercular bacili or viruses in cell mediated immunity T-cells release lymphokines which recruit (by chemotaxis) and activate other cells particularly monocytes and macrophages or act themselves (as killer cells) to attack host cells infected and try to kill them
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