B cells-Why one specificity

Mike Clark mrc7 at cam.ac.uk
Fri Dec 12 13:14:25 EST 1997

In article <3491177E.2FFE at marauder.millersv.edu>, Jay Mone'
<URL:mailto:jmone at MARAUDER.MILLERSV.EDU> wrote:
> The answers are probably not nearly as complicated as some would make 
> it seem.
> The genes encoding antibodies are found as several distinct loci on 
> chromosomes.  During the ontogeny of B cells, the cell randomly 
> selects one DNA sequence from each loci, and ligates them together.  
> The rest of the sequences which were not used are either spliced out 
> or are no longer functional.  After the gene sequences have been 
> selected, a functional antibody is produced.
> The catch is that this process is irreversible, and the cell has only 
> one chance to make a functional antibody due to the cutting up of the 
> loci which contribute the sequences.
> The resulting cell expresses a single antibody for the rest of it's 
> life span.  It can and often does change the class of antibody 
> produced, but the specificity is fixed.
> The body gets around the problem by producing millions of new B cells 
> daily, each with a uinique, randomly selected specificity.  This 
> process has served us well in evolutionary terms.
> Jay Mone'
What you say Jay is largely correct but there are of course two alleles and
the key observation is that immunoglobulin in B-cells is allelicly excluded
whereas the T-cell receptor alpha chain may not be. Similar processes of
DNA rearrangements occur for both of these two gene systems.

Mike Clark,                        <URL:http://www.path.cam.ac.uk/~mrc7/>
 o/ \\    //            ||  ,_ o   M.R. Clark, PhD. Division of Immunology
<\__,\\  //   __o       || /  /\,  Cambridge University, Dept. Pathology
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