There is reasonable evidence that genetic pressures help
to insure that offspring are different in the HLA loci from
the parents. The high variability of HLA molecules enlarges
the kinds of pathogens that can be recognized and eliminated
by an immune response within a population.
However, a disadvantage of high HLA specificity occurs during
organ transplants. The body recognizes the organ as non-self,
and launches an immune response against it. Proteins from
HLA genes are the cause of transplant rejections, and HLA
genotypes must be partially matched to improve outcomes of
Finally, studies on many species show that mating preference
and odor is somehow related to MHC alleles. Female mice prefer
to mate with males having different MHC loci. The immune advantage
of MHC diversity is apparently selected for during mating.