COMPARISON OF HAPLOTYPES OF THE MAJOR HISTOCOMPATIBILITY COMPLEX IN THE RAT II. SEROLOGICAL ANALYSIS OF THE HAPLOTYPES H‐1 a (Ag‐B4), H‐1 d (Ag‐B9) and H‐1 f (Ag‐B10)

SUMMARY The strongly cross‐reacting haplotypes of the inbred strains DA, ACI, ACP, MR, BD V and AS2, and of the congenic lines LEW.1A, LEW.1D and LEW. 1F, were explored. All of these inbred strains and these congenic lines type with anti‐Ag‐B4 antisera raised against the DA strain, which behaved as operationally mono‐specific in previously reported studies of the eight currently defined Ag‐B haplotypes. Serological analyses showed that this cross‐reactivity was due to antibodies against public antigenic specificities which were not previously recognized as being in the anti‐Ag‐B4 antisera, due to the fact that the LEW.1D and LEW. 1F animals were not available for testing. With the use of appropriate antisera and of absorption studies, two haplotypes in the H‐1 system were found not to have been previously identified in the Ag‐B system. The animals carrying the H‐1 d haplotype (MR, BD V and LEW.1D) have been designated as Ag‐B9, and those carrying the H‐1 f haplotype (AS2 and LEW.1F) have been designated as Ag‐B10. With the proper absorptions, an anti‐Ag‐B4 antiserum can be prepared which reacts only with the DA, ACI and ACP strains, and it will henceforth be used as the operationally mono‐specific Ag‐B4 typing reagent. A variety of typing experiments showed that the results using antisera raised in Pittsburgh and in Prague and using the Ficoll and dextran haemagglutination methods were the same.