MNS antigen system

The MNS antigen system is a human blood group system based upon two genes (glycophorin A and glycophorin B) on chromosome 4. There are currently 46 antigens in the system, but the five most important are called M, N, S, s, and U.

The system can be thought of as two separate groups: the M and N antigens are at one location on the ECM and S, s, and U are on a closely related location. The two groups are very closely located together on chromosome 4 and are inherited as a haplotype.

The MN blood group in humans is under the control of a pair of co-dominant alleles, L^M and L^N. Most people in the Inuit population are M/M, while this genotype is rare among Aborigines. In fact, they tend to possess the opposite genotype (N/N).

The MN blood group system is under the control of an autosomal locus found on chromosome 4, with two alleles designated L^M and L^N. The blood type is due to a glycoprotein present on the surface of red blood cells, which behaves as a native antigen. Phenotypic expression at this locus is codominant because an individual may exhibit either one or both antigenic substances. Frequencies of the two alleles vary widely among human populations.

M+ and N+ RBCs are common (75% of population) and M+N+ cells are the most common genotype (50% of population). These antigens were an early discovery and are some of the oldest blood antigens known after the ABO system. They were first described by Karl Landsteiner and Philip Levine in 1927. Anti-M and anti-N antibodies are usually IgM and are rarely associated with transfusion reactions.

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