I think that any definition of immunity with regard to invertebrates
must contain the assumption that invertebrates may evolve structures
that are evolutionarily analogous. That is, a component of the
invertebrate immune response could consist of a completely unique
family of molecules that accomplishes a similar objective such as the
neutralization of a foreign protein. The American cockroach is a
perfect example: Karp and collegues have demonstrated the presence of a
humoral immune response that exhibits both memory and specificity
towards soluble protein antigens, yet the response appears to be
mediated by a molecule that belongs to a family of vitellogenins (*not*
immunoglobulin). Similarly, a cellular response in the american
cockroach exhibits at least short term memory, but the responses are
mediated by cells that do not appear to have any relationship with
lymphocytes.
The question raised is an important one because if one assumes that an
immune response must me mediated *only* by lymphocytes etc., then the
situation is untenable because many inverebrates do not have the
physical structures for the generation of such cells. Yet, many
invertebrates are long lived -- i.e. the American cockroach can live as
long as two years (about the same as a mouse) and are therefore faced
with some of the same environmental pressures as many mammalian
species.
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James F. George, Ph.D. "Back off man, I'm a scientist"
Department of Surgery --Bill Murray
University of Alabama at Birmingham
205-934-4261 voice
txpljfg at uabcvsr.cvsr.uab.edu
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