| Abstract: | A recombinant haplotype of the major histocompatibility complex (H-1) of the rat has been found among F2 hybrids of two congenic strains, and it has been shown previously that the major gene determining mixed lymphocyte stimulation and the Ir-TGAL and Ir-PheGAL genes were separated from the genes determining the classical serologically detectable histocompatibility antigens. It has been shown that the complementing Ir-HGAL genes mapped together with the other Ir genes, and this gene cluster is assumed to represent the I region of the rat. Serological analysis of the recombinant is interpreted as showing that the Ir genes do not map in-between the genes controlling the classical histocompatibility antigens. Thus, the sequence of the major histocompatibility genes in the rat does not seem to follow that of the mouse H-2 system. Reciprocal immunization between the recombinant and the parental strain which shares the classical transplantation antigens but differs for the Ir genes, led t o the production of antisera which detected antigens with restricted tissue expression. These antigens were predominantly found on B lymphocytes and not on liver, brain or red blood cells and thus resembled mouse Ia antigens. Strain distribution analysis revelaed extensive cross-reactivity with most of the H-1 haplotypes, and two private specificities could be operationally defined. Thus, it is now possible to genetically define Ia antigens in the rat by the use of I region-congenic strains. |
