TOLERANCE INDUCTION BY ANTI-CD2 PLUS ANTI-CD3 MONOCLONAL-ANTIBODIES -EVIDENCE FOR AN IL-4 REQUIREMENT

Anti-CD2; mAb plus anti-CD3 mAb induce alloantigen specific tolerance. We sought to determine whether Th2 cytokines are involved in the indu ction of tolerance in this model. Addition of anti-IL-4 mAb or anti-IL -10 mAb to anti-CD2 plus anti-CD3 treatment abrogated tolerance and re sulted in graft survivals of 26 +/- 4 and 25 +/- 5 days, respectively. Splenocytes from the anti-IL-4 mAb and anti-IL-10 groups had greater proliferation in response to alloantigen than either tolerant or naive groups. Cytokine analysis of MLR supernatants showed increased IL-10 in the tolerant group and increased IFN-gamma in the anti-IL-4 mAb tre ated group. Donor-specific alloantibody responses in untreated immune animals had a predominantly Th1 (IgG2a) alloantibody response, while t he tolerogenic regimen reduced the ratio of IgG2a:IgG1 titers, The add ition of anti-IL-4 mAb to the tolerogenic regimen partly restored the Th1-related IgG2a response. Tolerance did not develop In IL-4 knockout animals treated with anti-CD2 plus anti-CD3 (mean graft survival, 27 +/- 5 days), Restoration of IL-4 to IL-4 knockout animals by gene tran sfer with plasmid DNA resulted in prolongation of survival to 46 +/- 7 days, while adoptive transfer of wild-type splenocytes into IL-4 knoc kout recipients resulted io indefinite graft survival (>60 dap) and In definite survival of second donor-type grafts. IL-10 gene transfer to IL-4 knockout recipients did not prolong graft survival (28 +/- 4). Th ese results demonstrate that tolerance in this model is mediated at le ast in part by Th2-type cells that secrete IL-4, promote IL-10 and IgG 1 production, and inhibit alloantigen reactivity.