bjheit at NOSPAM.ucalgary.ca
Thu Jul 24 18:20:42 EST 2003
Ok a few things:
Mike Clark wrote:
>That is possibly a true explanation but the same antibody did not react
>with human brain. I don't know if the levels of CD4 expression are
>different in human and sheep.
I believe in humans it's very low - you need a very sensitive assay to
detect CD4. This is true of many macrophage markers on microglea - some
people argue that because so many macrophage markers are downregulated
that microglea are not "true" macrophage.
>Included in there is analysis of a paper on antibodies to different species
>of lysozyme in which I point out that "specificity" and "affinity" are not
>easily related concepts.
I missed one point, although I don't know if this addresses the issue
you bring up. They compare the affinity of the "antibody to the
antigen" vs. the affinity of the antibody to a "random panel of
antigens" (cell lysate I believe). Specificity is measured as having
high affinity for the antigen with low affinity for random - but as I
mentioned earlier this may be specific (no pun intended) to their field.
>Yes but that is also partly because of a process of selection. The
>frequency of B-cells making an antibody of any given specifity might be low
>initially but it can be enhanced through selection and clonal expansion.
>What of T-independent immune responses, are they not also specific?
Never claimed they aren't. But AFAIK these antibodies still go through
affinity maturation and thus gain greater affinity compared to the
initial, naive B-cells.
>Look I'll give another example.
>I inject a mouse with human IgG as an antigen, and get back some
>monoclonals which react with human IgG1, IgG2, IgG3 and IgG4 equally. Other
>monoclonals react only with IgG1 but not with IgG2 3 or 4, and other
>monoclonals react only with the allotype G1m(1,17) but not G1m(3).
>So which of these monoclonal antibodies do you consider specific and which
>are not specific?
But in this case it is more likely the multi-reacting antibodies are
identifying shared epitopes between the different sub-classes. For
those antibodies I would say that they are specific to a shared epitope.
Considering the high degree of homology between the different IgG's it
is more then likely that they would be recognizing area's with 100%
>[snip] Must rush now. I'll deal with your other points tomorrow, but the
>Tour de France beckons.........
Wouldn't worry about it - I'll probably miss your post as I'm leaving
for a week of SCUBA Friday. Besides, we've gone a long way from the
origonal question (can I make one antibody that recognises 2 distinct
and unrelated proteins). That said, I would recommend the origonal
poster listen to you, as you obviously know more about this then I...
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