Identification of non-T suppressor cells with possible contra-interleukin-2 properties in non-human primates tolerant to their renal allograft

Pre-transplant conditioning with total lymphoid irradiation (TLI)induces antigen non-specific suppressor cells in the circulation of baboons. This study aims to identify the properties and phenotypes of cells imparting suppression of mixed lymphocyte cultures (MLC) from TLI and non-TLI conditioning animals. The MLC consisted of recipient responder T cells stimulated with pooled normal mononuclear cells (MNC) with suppressor MNC, autologous to the responding cell, added at intervals after transplantation. Suppression was non-specific and MLC proliferation was down-graded by MNC isolated from long surviving animals. Suppression was mediated by a soluble product which could pass a 0.4 micron cellulose membrane in a specially designed well insert. Addition of exogenous IL-2 failed to reverse suppression, but complete reversal was achieved by treatment of suppressor MNC with L-leucyl-L leucine methyl ester. Additionally, depletion of CD11b(+) and CD38 (+)MNC from suppressor cells significantly reversed MLC inhibition. Consequently, the suppressor cells appear to express phenotypes common to monocytes and possess contra-IL-2 properties. Consequently these cells may function by skewing T cell responsiveness away from allo-antigen reactivity in vivo.