Antibody's specifity...

[Bryan Heit]

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.

><snip>
>
>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% 
protein homology.

><snip>
>
>[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...

Bryan