| The 10/10 match refers to HLA typing: http://en.wikipedia.org/wiki/Human_leukocyte_antigen These are the human MHC molecules that present antigen to T-cells. Unfortunately for the transplant process, a vast number of HLA alleles exist for each locus. This is important evolutionarily for population disease aversion, but makes the process of finding a match very difficult. Central tolerance makes our immune system unreactive to self antigen. Foreign HLA present in tissue grafts will never be screened out by negative selection since this process requires expression of our own genes to cull any B or T cells that are self-reactive. Anything foreign will most certainly have reactive cell-surface epitopes (to varying degrees of reactivity). Try reading up on central tolerance, somatic recombination, and clonal selection if you get the chance as it's a beautiful example of nature stumbling upon metaheuristic optimization: http://en.wikipedia.org/wiki/Central_tolerance http://en.wikipedia.org/wiki/Clonal_selection http://en.wikipedia.org/wiki/V(D)J_recombination To me, these are starker, more potent examples of biological optimization processes than evolution -- they're ongoing in your body right now. |