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
"> || _`\<,_ // \\ \> | Tennis Court Rd., Cambridge CB2 1QP
` || (_)/ (_) // \\ \_ Tel.+44 1223 333705 Fax.+44 1223 333875
