Of course, any one human can inherit a maximum of two alleles at each locus. The diversity of alleles in the population makes possible thousands of different combinations. Another 111 donors had a set of these molecules that they shared with only one other person in the group. The extreme polymorphism of the MHC did not evolve to frustrate transplant surgeons and their patients. Discussion of antigen presentation by class I and class II molecules.
Different parasites generate different antigenic fragments.
Different MHC molecules differ in the efficiency with which they bind particular sequences of amino acids in these fragments. Therefore, we might expect that some MHC products would be better than others at presenting parasite antigens to the immune system. So it may well be that the great diversity of class I and class II alleles in the human population has helped ensure that no single parasite can wipe out the entire population. Coming into wider use is DNA typing , especially for HLA-D antigens. It promises to improve the sensitivity and specificity of tissue typing.