Major Histocompatibility Complex

MHC genes are called HLA (human leukocyte complex) for human. Sixth chromosome contains 4 loci of HLA genes (HLA-A, HLA-B, HLA-C, HLA-D). Each of these is polymorphic – there are many alleles within human gene pool. There is very low probability for not related persons to have the same arrangement. Siblings have 25% chance to have the same genes and therefore be HLA matched. Both have to inherit the same mother’s sixth chromosome (50% chance) and father’s sixth chromosome (50% chance).

Major histocompatibility proteins are treated like antigens and strives to what leads to rejection of transplanted organs. When members of the family can’t be donors finding person that is HLA matched is difficult. It is being studied how to reduce immune reaction so that transplant is not rejected.