Immunity

David Adler dadler at u.washington.edu
Wed Jan 22 00:10:02 EST 1997


>BILLMOULD at aol.com wrote:
>
>:  I recently read in a non-science related book that women have twice the
>: immunity that men do since they have two X chromosomes.

Maybe what is meant, although stated oddly, that females have more cell  
diversity because of random X-chromosome inactivation - see below:

On 01/14/97, William Tivol wrote:
>Dear Mary and/or Bill,
>	 Everyone has two of each of their other pairs of chromosomes, and
>the Y chromosome has genes, so the only way men would be cheated out of
>immune system potential is if the genes for immune system production were on
>that part of the X chromosome which has no counterpart on the Y.

Most X-linked genes do *not* have counterparts on the Y chromosome. 

>Furthermore, stem cells for immune cells inactivate one of the chromosomes and
>produce antibodies (or immune cells) from only one chromosome, so it does not 
>matter whether the cell is male or female.

But, a consequence of random X-chromosome inactivation, in early development, 
and the subsequent stable maintenance, is that females are cell *mosaics* for 
any X-linked gene for which she is heterozygous (i.e. half her cells expressing 
the maternal allele, half expressing the paternal allele). So, one can imagine, 
although I cannot give an example of a  specific X-linked immune locus, that 
women may be more "adaptable"  because they express two alleles, albeit in 
separate cells. Males, on the other hand, are hemizygous for X-linked genes, or 
in effect homozygous with only one allele present in all cells.

>	It is still possible that women's immune systems are stronger than
>those of men, and it may be related to the X chromosome.  Other genes on the
>X may have a lot to do with overall health, and these may provide a better
>environment for the production and survival of immune cells--after all, 
>there must be *some* reason that women live longer than men.

There are also X-linked genes that "escape" X-inactivation and for these genes 
there *would be a gene dosage difference* between males and females. Of course 
other factors also influence immune response and may differ between the sexes, 
such as hormones. Hope this all makes sense.

Does anyone know of an X-linked immune locus that might be relevant?

thanks,
David

-- 
David Adler, Ph.D.
scientist
"Science is nothing but trained and organized common sense"
T.H.Huxley



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