The MNSs Blood Group System

Abstract

The two major human red cell agglutinogens M and N were discovered in 1927 by Landsteiner and Levine by means of reagents obtained from the sera of rabbits immunized with human group O cells (Landsteiner and Levine 1927a,b). The anti-M and anti-N reagents so obtained defined three MN types in human blood, M, N and MN, attributed to the action of two codominant alleles, M and N,which combined in three possible genotypes: MM, NN or MN. Extensive family studies and the application of gene frequency analysis to studies on the distribution of the MN types in various human populations yielded results consistent with the genetic theory proposed by the discoverers of this blood group system. In 1947, Walsh and Montgomery discovered an alloantibody in the serum of the mother of an erythroblastotic baby. The antibody, called anti-S, defined a new antigen, S, which was found to be associated with M or N. A few years later, Levine et al. (1951) discovered another alloantibody in the serum of the mother of an erythroblastotic infant. The serum gave reactions anthithetical to anti-S and was therefore named anti-s; the corresponding antigen was called s. Antigens S and s were found to depend on two codominant alleles, S and s. Evidence of recombination between MN and Ss genes implied the independence of the two loci, but the rarity of the occurrence of such recombination pointed to their genetic closeness.