Expression of MHC class II and Tac antigens on IL2-activated human T cell clones that can stimulate in MLR, AMLR, PLT and can present antigen.

The expression of interleukin 2 (IL2) receptor and HLA-DR, DQ, and DP antigens on the surface of four diphtheria toxoïd (DT)-specific T lymphocyte clones (TLC) and two TLC specific for an allogeneic EBV-transformed cell line was investigated with the use of monoclonal antibodies (MoAbs) that recognize defined molecules or epitopes. Incubation of a resting TLC with IL2 resulted in a 10- to 30-fold increase in the level of DR, DQ, and Tac antigen expression. On the other hand, incubation of an activated TLC with IL2 decreased for 1 to 6 hr the level of expression of these three antigens. Anti-FA MoAbs did not react with any of the TLC tested suggesting that the expression of DR, DQ, and DP antigens is dissociated on activated TLC. Surface-marker analysis with anti-DR MoAbs indicated that DR epitopes were differently expressed at some activation stages of the TLC. Functional studies showed that activated TLC can stimulate in MLR, AMLR, and PLT. These proliferative responses were inhibited by preincubating the TLC with anti-DR MoAbs suggesting that the stimulatory determinants were predominantly DR molecules. In addition, some TLC can act as antigen presenting cells in DT-specific proliferative responses. These results indicate that MHC class II molecules on activated T lymphocytes may be relevant for the control of specific immunologic responses in vivo.