- During the initial several days following the injection
of an antigen in an individual that was not previously exposed to the
antigen, no antibodies are detectable (lag period).
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- Antibody production would then rise over time to peak
and then to decline, ultimately approaching the baseline. This initial
production of antibody is called the primary response. The initial response
is mainly due to IgM with IgG appearing later.
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- If an individual has previously made an immune response
to a given antigen, a subsequent exposure to that antigen results in
a much more rapid rise in antibody to a more prolonged, higher level
.
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- The ability to make a secondary response is absolutely
dependent on prior exposure to the antigen in question - it is thus
an antigen specific phenomenon. In essence the individual has IMMUNOLOGICAL
MEMORYof that antigen. This memory may last for periods of years for
some immunogens up to decades for others.
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- during the primary immune response the immunogen "selects"
from the pool, those cells which recognize it and activates them to
undergo proliferation and begin synthesizing antibodies. Due to the
relatively low number of cells specific for any given antigen, this
process takes some time to get going, (the lag period). The activated
cells undergo a limited number of doublings and then cease proliferating
and synthesizing antibodies. By the end of this primary response a significant
increase in the number of lymphocytes capable of recognizing the inducing
antigen have been produced -MEMORY CELLS.
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- Because of the larger number of cells, the chances
of early encounters with subsequent "challenges" by the antigen
are greatly enhanced resulting in significant shortening of the lag
phase. Additionally, the increased number of responding cells results
in much higher levels of antibody being attained with subsequent challenges.
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