HLA system in solid organ transplantation part 17

For both class I and II HLA molecules, most of the polymorphic residues reside in the regions forming the peptide-binding groove. The great polymorphism  of HLA genes has been maintained through evolution due to their central role in initiating and regulating immune responses rather than due to their role determining histocompatibility or risk for rejection. For conventional immune responses, eg against infections, the greater the polymorphysm within the MHC genes, the greater the advantage a species will have to survive through  epidemics, since this  will provide that species with a wider responsive repertoire and the capacity to counterattack immunologically. In other words, without the diversity of the MHC molecules, if a given agent mutated in the way that their peptide antigens could not longer sit on the binding groove of the MHC molecules of a given species, the responding species would definitively succumb due to incapacity to defend itself against the threat.