Immune Responses To Noninherited Maternal Rtia Antigens in Inbred Rats

Humoral responses to noninherited maternal class I antigens (class I NIMAs) were assessed in 3 groups of inbred rats expressing the RT1u phenotype. Group 1 consisted of the progeny of (AOxDA)F1xPVG matings; their haplotype was RT1u/c and their noninherited maternal haplotype RT1a. Group 2 were the progeny of (AOxLEW)F1xPVG matings the haplotype of which was also RT1u/c, but their noninherited maternal haplotype was RT1l. Group 3 comprised 8 (AOxPVG)F1 (RT1u/c) hybrids. All rats received 2 intravenous blood transfusions (0.5 ml) from male DA (RTlA(a)) donors on days 0 and 7. They were bled at weekly intervals for 6 weeks and again at 20 weeks after the first transfusion. Alloantibody responses to RT1A(a) were assessed by an indirect hemagglutination assay (IHA)* and by a Chromium-51-release complement-dependent red cell cytotoxicity assay.

All groups exhibited vigorous anti-class I antibody responses to the DA transfusions. No significant differences were detected, however, in antibody titers between the groups either by IHA or CDC or in the rates of decay of antibody titers up to week 20. In addition no blocking activity was found in sera obtained on day 0 from group 1 animals and tested for antiidiotypic antibody activity to cytotoxic anti-RTlA(a) antibodies. In order to assess whether suppressor activity had been activated by the initial transfusions, in the animals in which class I NIMA was RT1A(a), all groups were rechallenged with a DA transfusion at week 20. All animals exhibited vigorous anamnestic responses to this challenge and no significant differences were detected between groups.

In order to determine whether cellular tolerance to the noninherited maternal haplotype was present in group 1 animals, proliferative responses were assessed by one-way mixed lymphocyte cultures, using DA lymph node stimulator cells. No significant differences were detected in proliferative or kinetic responses between lymph node cells from rats the noninherited maternal haplotype of which was RT1a or from naive (AOxPVG)F1 hybrids. Peak proliferative responses to DA cells in rats the noninherited maternal haplotype of which was RT1l were similar, but maximal on day 4 as opposed to day 3.

Hence in these inbred rat strains no evidence of humoral tolerance to class I NIMAs was detected. In addition there was no evidence of cellular tolerance to the noninherited maternal MHC haplotype.