Serological inhibition of blast transformation to purified streptococcal antigens by planned immunization in HLA (A,B) compatible unrelated individuals.

Sera obtained from planned immunizations between unrelated donors and recipients, identical or compatible at HLA-A and B, were assessed for their capacity to alter the in vitro response of a test panel of lymphocytes to PHA and a purified streptococcal antigen (PAS). In the case of PHA, no serum effects were apparent. The response to PAS, however, significantly inhibited by two sera. When tested for their complement-dependent cytotoxicity on enriched populations of T and B lymphocytes, none of the sera manifested cytotoxicity against T cells nor did serological inhibition correlate with the capacity to lyze B cells. The data suggest that inhibition of the PSA response is mediated by blocking antibodies specific for a subset of lymphocytes, possibly T cells. While the precise mechanism governing the response to PSA is not known, the data are compatible with the idea that an HLA-linked Ir gene, expressed on a subset of T lymphocytes, controls immune responsiveness to PSA.