c. Secondary Response. The next time the same antigen enters the same
body, it stimulates a rapid increase in the production of a large number of antibodies.
This is called the secondary response.
d. End Result. When the antigen is reintroduced into the body, antibodies react
with the antigens by several mechanisms that either inactivate or destroy the antigen.
The end result is that the antigen is unable to harm the body.
e. Antigen-Antibody Reactions. There are four types of antigen-antibody
reactions that occur in the body.
(1) Agglutination occurs when antibodies attach one bacterium to another.
The bacteria then form one large mass. This massing effect not only prevents tissue
invasion by the bacteria, but also makes them more susceptible to phagocytosis.
(2) The second reaction, precipitation, occurs when antigens, which are
soluble in plasma, are attached to one another by antibodies. When enough antigens
and antibodies are combined, they form a solid mass that is insoluble and thus
precipitates out of solution. The insoluble particles are then engulfed and digested by
(3) The third reaction is neutralization. Antibodies attach themselves to the
reactive sites of antigens that have entered the body. Consequently, the toxin is
neutralized and can no longer harm the body. The antigen-antibody complex is then
engulfed by phagocytes. This process works well on both toxins and viruses.
(4) The fourth reaction is referred to as lysis of the organism. Here,
antibodies attach themselves to bacteria, viruses, or other foreign cells. When the
antibodies react with these cells, complement, a substance present in blood plasma,
penetrates the cell membrane of the organism, which causes it to rupture.
a. Active Imunity. Active immunity results when antibodies are produced by
the body as a result of stimulation by living, dead, or attenuated organisms or their
toxins. Immunity of this type develops slowly and become effective in several weeks.
Usually, active immunity is both complete and enduring.
b. Types. Active immunity can be divided into two types. First, natural active
immunity is antibody formation stimulated by the presence of living organisms or their
products that cause disease. In other words, you get the disease. Life-long immunity
usually results from having a disease in which natural immunity can result. Second,
artificial active immunity is antibody formation stimulated by the administration of a