Antibody's specifity...

Ian A. York iayork at
Wed Jul 23 19:54:21 EST 2003

In article <3F1F1222.9000403 at>,
Bryan Heit  <bjheit at> wrote:
>Mike Clark wrote:
>>Antibodies may or may not be "specific" depending upon how they
>>are selected and how in practice you define specificity. Specificity is not
>But how many times have you run a cell lysate blot with an antibody and 
>seen greater then 1 line?  It's rare, and when it does occur it's 

Many, many times.  

>usually human error or a closely related protein.  In all of the blots 
>and elisa's I've done (that's a lot) I've never once encountered an 
>antibody with cross reactivity for a non-related protein, and that 
>includes some "dirty" polyclonal serums I derived myself.

Many of the polyclonals I've raised, and many of those we've got from 
various collaborators, cross-react.  Rabbits see *lots* of antigens even 
in their constrained little lives in a lab cage, not just the ones you 
inject.  Those may not be formally cross-reactive (i.e. the same clonal Ig 
may not be reacting with two antigens) but the result is the same.

I've also seen a few monoclonals that cross-react with unrealted proteins, 
though not very many.

>Can you cite a single occurrence where antibodies show cross-specificity 
>with a protein only 50% identical, unless it is recognizing a shared 
>epitope?  I did a quick check of pubmed and could not (not to say there 
>isn't, I didn't look too closely).

Most of the cross-reactive antibodies are simply thrown away, they're not 
worked up to the point of eliminating shared epitopes (an artificial 
constraint you've added to the original question).  By the time they're 
published, you're generally only seeing the best (i.e. most specific) 
antibodies.  Depending on the published literature for this question is 
not particularly useful.

>Or you could look at it as a group of antibodies all recognizing the 
>same antigen.  Idiotype antibodies are a special case, as it is hard to 
>identify what is the "antigen" and what is the "antibody".  As I said 
>previously, I am unaware of any study showing cross reactivity between 
>proteins with little/no homology.

I've certainly seen cross-reactive monoclonals.  Were they reacting with 
shared epitopes, with closely-related proteins, with unrelated stuff?  I 
have no idea.  I threw them away, because they were useless for my 
purpose.  That's what happens to most of the cross-reactive antibodies.  


    Ian York   (iayork at  <>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England

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