IMMUNITY

IMMUNITY

Immunity is the defence mechanism that protects an individual (host) from infectious diseases. They are of two types, viz. innate immunity and acquired immunity. Innate immunity is the inherited immunity. It acts as a first line of defence against infectious agents and does not exhibit any specificity. Innate Immunity may be considered at the level of species, race or individual.
The resistance that an individual acquires during life is known as acquired immunity. This type of immunity exhibits specificity. A particular infectious agent induces lymphocytes to proliferate, mature, secrete and “remember” that particular agent (primary immune response). Subsequent infection by the same parasite produces increased resistance and is called secondary immune response.
Acquired immunity has four essential features. They are as follows:
· An Induction phase,
· Recognition,
· Specificity and
· Immunological memory.
Acquired immunity is meditated by two interrelated and interdependent mechanisms – humeral immunity and cell meditated immunity. In humoral immunity the active proteins component, immunoglobulin’s (antibodies), are present in cell- free portion of the blood (plasma or serum). These immunoglobulins are specific for the infectious agents (antigens). They are derived from bone marrow lymphocytes or B-cells. Thymus-derived T-lymphocytes or T-cells reside in the peripheral blood and lymphoid tissues, which comprise the cellular component of the immune system. The infectious agents or their products stimulate the proliferations and differentiations of the T-cells and its progeny for the defence action.