الفهرس 
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Abstract
As animal species evolved, many specialized organ systems developed to help to protect individuals in their environment. Several of these systems are nonspecific, but very effective. In addition to these, there is another system that specifically recognizes and responds to foreign substances, or antigens. This system, the immune system, elaborates specific products and triggers inflammatory processes to eliminate the antigen (Scott and Dawson, 1985).
When a foreign substance enters the body, two different types of immune responses may occur. The synthesis and release of free antibody into the blood and other body fluids is the first reaction and is called “humoral immunity”; as the word humor designates body fluids (Myrvik and Weiser, 1984; and Roitt, 1984). The other reaction is the production of sensitized lymphocytes which are themselves the effectors of cell-mediated immunity (Roitt, 1984). The humoral immune response defends primarily against the extracellular phases of bacterial and viral infections, and is mediated by various classes of immunoglobulin circulating through serum and lymph.
Antibodies have unique specificities which bind antigen
and are both highly specific and capable of mediating destruction of organisms or virally infected cells either directly through fixation of the complement or through attachment to various effector cells (Hood et aL, 1984; and Roitt, 1984).
Cell mediated responses are primarily mediated by T lymphocytes and macrophages which induce intense cellular reactions to invading pathogens. This arm of the immune system is responsible for resistance to many parasites, tumors and intracellular pathogens (Bellanti et al., 1985; and Hood et al., 1984).