Section II. IMMUNE RESPONSE
Immune response is defined as a reaction due to an antigenic stimulus
characterized by the formation of humoral antibodies or the development of cellular
immunity or both.
SPECIFIC IMMUNE RESPONSE
Specific immune responses are concerned with the recognition and ultimate
disposal of foreign substances. The responses are made up of a series of cellular
interactions, including the elaboration of specific cell products. Three general
characteristics that distinguish specific immune responses are:
a. Specificity. This is the property of the specific immune response that
distinguishes one antigen from another. The products of the immune response will
react solely with the antigenic configuration identical or very similar to that which
initiated the response.
b. Heterogeneity. This is characterized by the induction and interaction of a
variety of new cell types specific for the inducing antigen. Heterogeneity contributes a
fine degree of homeostatic control with which the host can respond in a highly variable
and specific manner to foreign structures. In other words, heterogeneity is the body's
way of proving "There's more than one way to skin a cat."
c. Memory. This is the property that results in proliferation and differentiation of
sensitized cells upon subsequent exposure to an immunogen.
Three phases of antigen removal take place following exposure.
a. The first phase takes only 10 to 20 minutes and represents the time required
for equilibration of the antigen with the tissues and fluids. Because of extensive
phagocytosis in the liver, lungs, and spleen, nearly 90of the antigen is removed from the
circulation in its first passage through these organs.
b. The second phase of antigen elimination is a phase of gradual catabolic
degradation and removal. This phase lasts for 4 to 7 days and represents the gradual
enzymatic hydrolysis and digestion of the antigen. Consequently, the limits of this
period are regulated by the enzymatic capability of the host for the particular type of
substrate making up the antigen.
c. During the third phase, there is accelerated removal of antigen, as a result of
the combination of newly formed antibody molecules with the antigen, enhancing the