Limiting Dilution Analysis of Alloantigen‐Reactive Cells which Respond to Allogeneic Lymphocytes in Human MLC and PLT

Abstract

We have determined the frequency of the alloantigen-reactive cells (ARC) in human ILC and PLT by the limiting dilution analysis. In PLT, the frequency of the ARC to the original sensitizing donor ranged between 1:32 to 1:62, an increase of six to nine-fold after priming in MLC. The MLC primed populations were also enriched (three to five fold) for the ARC responding to the PL-positive allogeneic donors. The incidence of the ARC was 1 6 2 to 1:118 with donors positive for the sensitizing HLA-DRw antigen and 1:77 to 1:144 with donors negative for the specific HLA-DRw determinant. The results from experiments utilizing pooled stimulating cells from the original and allogeneic donors suggest that same subpopulation of cells responds to :he sensitizing HLA-DRw determinant, whether it is presented by the specific stimulator or by a thirdparty allogeneic donor. On the other hand, different subpopulations of alIoreactive cells respond t o different alloantigens.In MLC experiments between HLA-identical siblings, the incidence of the ARC ranged between 1:995 to 1:1673. The responses of the ARC to non-HLA antigens were observed under conditions where responder cells were limiting. Also, the responses of the limiting numbers of responding cells were inhibited by mitomycin-treated autologous lymphocytes. Nonresponse in MLC combinations with higher responder cell numbers was not due to small numbers of stimulating cells.