The major histocompatibility complex of the rat,RT1 : I. serological characterization of the MNR haplotype (RT1 ( m )) in regard to the cross-reacting haplotypesRT1 ( a ),RT1 ( c ), andRT1 ( b ).

The antigenic determinants expressed on RBC and lymphocytes and coded for by the MHC, RT1,of the MNR (RT1 ( m )) rat strain were compared to those of the BN.DA(RT1 ( a )), ALB (RT1 ( b )), and AUG (RT1 ( c )) strains by direct cytotoxicity and absorption analysis with RT1 typing sera, sera produced against MNR cells, and sera produced in MNR responders against cells carrying thea, b, andc haplotype determinants. The results indicate that MNR shares major class I (A) antigens with DA, and major class II (B) determinants with AUG, but that MNR differs from DA and AUG with respect to both classes of determinant. It appears, therefore, that the MNR haplotype does not represent a simple composite of the two other haplotypes,RT1 ( a ) andRT1 ( c ), as reported earlier.