| Abstract: | Two antisera to Ia antigens, products of the H-2 complex I-Cd and I-JkEk subregions, respectively, have been obtained by immunisation of the F1 hybrids of recombinant strains of mice. These antisera are shown to display the 50 per cent cytotoxic effect in vitro in the presence of complement upon lymphocyte populations immune to the H-2 complex antigens and enriched for specific suppressor T cells (SSC) by fractionation on the monolayer of target cells. The specificity of anti-Ia cytotoxins is shown by the cross antibody absorption with T- and B-cells of mice originated from the recombinant H-2 haplotypes and bearing either particular I-Cd, I-Jk and I-Ek antigens, or their combinations. Anti-I-Cd cytotoxins are found to react with both B and T cells at a different rate, and the anti-I-JkEk serum contains two antibody types directed to I-Ek and I-Jk products, respectively, the latter being able to react preferently with T cells. Although both antisera do inactivate the in vitro SSC function in the presence of complement at a similar degree, the inactivating action of the anti-I-Cd serum, but not that of the anti-I-JkEk serum, occurs without complement. SSC are established to bear both Ia-antigens, I-J and I-C on the same cell, as demonstrated by the cross antibody absorption and variation of the H-2 origin of SSC. These two markers are suggested to function differently in the SSC immune to the H-2 antigens and the I-C antigen expression on the SSC surface is presumed to be required for their interaction with the inhibited responder T cells proliferating in MLC. |
