What is an antigen?

[Mike Clark]

In article <4nafqv$fue at agate.berkeley.edu>, Ken Frauwirth
<mailto:frauwirt at bacillus.Berkeley.EDU> wrote:
> In article <3495778.ensmtp at eureka.qc.ca>,
> Yves Blais <Yves_Blais at EUREKA.QC.CA> wrote:
> >any answers welcome...
> The only answer that I know is a functional one - an antigen is any substance
> which can elicit an immune response.
> 
No what you are describing is an immunogen! In the context of an antibody
an antigen is any substance to which the antibody can bind with detectable
affinity (via it's Fv!). I guess that it would also be possible to
extend this definition to peptides presented by MHC as recognised
by T-cell receptor.
Not all antigens are immunogenic but all immunogens are antigenic. Often
an immunogen will elicite an immune response which cross-reacts on many
antigens.

Mike Clark, mrc7 at cam.ac.uk          http://www.path.cam.ac.uk/~mrc7/
-- 
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