R24 ANTI-GD3 GANGLIOSIDE ANTIBODY CAN INDUCE CO-STIMULATION AND PREVENT THE INDUCTION OF ALLOANTIGEN-SPECIFIC T-CELL CLONAL ANERGY

R24 is a monoclonal antibody directed against the cell surface ganglio side GD3. It can detect GD3 on the surface of a subset of T lymphocyte s and can stimulate proliferation and secretion of cytokines in vitro. In the present report, we examined the effects of the R24 antibody up on antigen-specific T cell response, employing an HLA-DR7-specific T c ell clonal model. As previously shown, primary stimulation of HLA-DR7- specific alloreactive T cell clones by transfectants expressing HLA-DR 7 alone (t-DR7) in the absence of B7 co-stimulation resulted in anergy . Binding of cell surface GD3 on HLA-DR7-specific alloreactive T cell clones with R2 it under these anergizing conditions resulted in interl eukin-2 (IL-2) accumulation and prevented the induction of alloantigen -specific T cell clonal anergy. Binding of GD3 by R24 also prevented a nergy under conditions where B7:CD28 interactions were blocked by CTLA 4-Ig. The effect of R24 was abrogated in the presence of a combination of monoclonal antibodies for the alpha and beta chains of the IL-2 re ceptor (IL-2R) or a neutralizing anti-IL-2 antibody. R24 does not appe ar to interact directly with the IL-2R since incubation of T cell clon es with R24 did not induce early activation of IL-2R associated Jak ki nases, Jak1 and Jak3, as was induced following incubation with IL-2. I n contrast, incubation of HLA-DR7-specific clones with t-DR7 in the pr esence of R24 did result in phosphorylation of IL-2R related Jak kinas es after 24 h. Our data indicate that the membrane ganglioside GD3 str ucture recognized by R24 may play an important role in antigen-specifi c T cell clonal response.