On Fri, 5 Nov 1999, Wally Day wrote:

> Thanks for reply. Now, could someone enlighten me
> about how the body recognizes a protein as being
> foreign? Is it a different amino acid profile? A
> specific amino acid? Or some other substance that
> "contaminates" the protein?

Proteins in general are distinguished by their shape, which is a
function of the amino acid sequence causing it to fold in
specific ways.

For example, the neurotransmitter dopamine has a particular shape
that allows it to fit into the dopamine receptors on neurons in
the brain.  Cocaine contains a protein that also fits into those
receptors because it is similar in shape to dopamine.  Once in
the receptor, it stays there longer than the dopamine would, so
its effect on the brain is not quite the same.  In this case, the
body fails to recognize the cocaine as foreign, so nothing
inteferes with its transit to the brain.  In other cases, the
proteins enter the blood and set off an immune system alarm, so
to speak, by clumping red blood cells which in turn triggers the
deployment of macrophages to engulf the enclumped protein and
destroy it.

Todd Moody
[log in to unmask]