Anti‐N Reagents in Elucidation of the Genetical Basis of Human Blood‐Group MN Specificities¹

Studies of the reactivity of the various anti‐human blood group N reagents with isolated human blood group M and N antigens and smaller molecules revealed besides the expected interaction with N antigens that M antigens inhibited all rabbit anti‐N sera, Vicia graminea extract and most human anti‐N sera. Mild acid hydrolysis of M antigens, which released sialic acid only, led to a large increase or de novo appearance of this inhibitory capacity. The partially hydrolyzed M antigens became temporarily indistinguishable from N antigens, indicating that the product of the N gene is the immediate precursor of the product of the M gene and that the allele to the M gene is an amorph. In the NM biosynthetic pathway, the Vicia ‐reactive structure seems to precede the N‐specific molecule. Uncovering of N‐specific structures paralleled the appearance of terminal β‐ d ‐galactopyranosyl structures; their exposure to β‐galactosidase resulted in destruction of N specificity. Galactose and some β‐ d ‐galactopyranosyl derivatives inhibited the N erythrocyte agglutination by some anti‐N sera. Ganglioside I and ‘asialoganglioside’ were inhibitors of anti‐N reagents and anti‐ganglioside serum reacted preferentially with human blood group N antigens.