Strong lymphoproliferative suppressive function of PLT clones specific for SB-like antigens.

From a total of 37 different priming combinations between donors matched for HLA-A,B, and/or Dw/DR, but mismatched for SB, antigens, T cell clones strongly restimulated with concordance for SB specificities were isolated from only two. Most of the alloproliferative (PLT) clones obtained were restimulated by determinants not correlated with any currently known HLA product. Nonetheless, their stimulation was inhibited by a monoclonal antibody TU 39, which preferentially blocks stimulation by SB-, rather than by Dw/DR-associated determinants. Despite having an OKT4+, OKT-, Leu8- phenotype, and secreting Interleukin-2 after contact with stimulatory cells, these clones strongly suppressed proliferative responses of cloned PLT reagents as well as unprimed lymphocytes in mixed leukocyte cultures. They may thus represent a novel type of immunoregulatory T cell, stimulated by SB-related antigens, which despite their "helper/inducer" phenotype are able directly to suppress lymphoproliferative responses.