17.
The first phase of antigen removal takes only 10 to 20 minutes and represents
time required for equilibration of the antigen with the tissues and fluids. Nearly
90% of the antigen is removed from the circulation in its first passage through the
liver, lungs, and spleen by extensive phagocytosis. (para 1-5)
18.
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. (para 1-5)
19.
During the third phase, removal of antigen is accelerated by the combination of
newly formed antibody molecules with the antigen, enhancing phagocytosis.
(para 1-5)
20.
A primary immune response occurs when an individual first encounters a foreign
antigen. After antigen exposure, there is a lag of several hours to several days
before antibody is detected. This latent period depends upon the kind and amount
of antigen given, the route of administration, and other host-dependent factors.
Antibody appears between the fifth and tenth day. (para 1-6a)
21.
After the first exposure to an antigen, the lag before response is called the latent
period. This lag is due to two factors. First, it may take several days before
enough antibody is produced for it to be measurable. Second, the first antibody
molecules may be excreted in combination with residual antigen and thus not
detected. (para 1-6a(1))
22.
After the latent period ends, the primary antibody response becomes detectable.
The titer of antibody gradually increases over a period of a few days to a few
weeks, plateaus, and then begins to drop. The initial antibody formed in the
primary response is IgM. During the first and second week, IgM production
declines. Evidence suggests that a single precursor B cell can give rise to a clone,
which can switch from IgM to IgG production. This phenomenon is referred to as
the IgM-IgG shift. IgG production declines after a few weeks. (para 1-6a(2))
23.
With subsequent exposure to antigen, the antibody response differs dramatically
from the primary antibody response. This secondary response is characterized by
a sharp drop in circulating antibody because it complexes with the newly injected
antigen. Immediately thereafter, a marked increase in antibody levels becomes
evident; the antibody is primarily IgG. Ultimately, the titer far surpasses that of the
primary response and has a more extended duration. (para 1-6b)
24.
Current theories of immunoglobulin formation include clonal selection theory and
template or instructive theory. (para 1-7)
MD0838
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