| |
Immunity
is the ability of an individual to recognize the "self" molecules
that make up one's own body and to distinguish them from such
"non-self" molecules 
as those found in infectious microorganisms and toxins. This process
has a prominent genetic component. Knowledge of the genetic and
molecular basis of the mammalian immune system has increased in
parallel with the explosive advances made in somatic cell and
molecular genetics.
There are
two major components of the immune system, both originating from
the same precursor "stem" cells. The bursa component provides
B lymphocytes, a class of white blood cells that, when appropriately
stimulated, differentiate into plasma cells. These latter cells
produce circulating soluble proteins called antibodies or immunoglobulins.
Antibodies are produced in response to substances called antigens,
most
of which are foreign proteins or polysaccharides. An antibody
molecule can recognize a specific antigen, combine with it, and
initiate its destruction. This so-called humoral immunity is accomplished
through a complicated series of interactions with other molecules
and cells; some of these interactions are mediated by another
group of lymphocytes, the T lymphocytes, which are derived from
the thymus gland. Once a B lymphocyte has been exposed to a specific
antigen, it "remembers" the contact so that future exposure will
cause an accelerated and magnified immune reaction. This is a
manifestation of what has been called immunological memory.
Francis
Collins
|
|