Induction of apoptosis in activated T cell blasts by suppressive macrophages: A possible immunotherapeutic approach for treatment of autoimmune disease

Large suppressive macrophages (LSM)were induced by restimulating spleen cel ls from rats with experimental autoimmune myasthenia gravis (EAMG) in vitro , with the autoantigen acetylcholine receptor (AChR) in the presence of cyc losporine A. LSM, purified from these cultures, are extremely potent suppre ssors of AChR-stimulated lymphoproliferative responses and antibody respons es in vitro. In the present study, we have analyzed the factors that determ ine susceptibility of primed lymph node cells (pLNC) to suppression by LSM and examined the fate of these cells. We found three characteristics of pLN C that influenced their susceptibility to suppression. First, pLNC were req uired to be activated (by antigen in these experiments) in order for suppre ssion to occur. Resting lymphocytes were not affected, even when they were present in cultures where antigen-activated lymphoblasts were being activel y suppressed. Second, antigen specificity of the responder cells influenced their susceptibility to suppression by LSM. AChR-specific cells were relat ively more susceptible to suppression by AChR-induced LSM than pLNC primed to an unrelated antigen, keyhole limpet hemocyanin. Third, T cell prolifera tion was suppressed by LSM to a far greater extent than antibody production by B cells. Using enriched T cell blasts generated from AChR-stimulated T cell lines, we found that LSM rapidly suppressed [H-3]TdR uptake and induce d DNA fragmentation assessed by the TUNEL assay (within 8 h of coculture) a nd induced morphological signs of apoptosis of T cells (within 24 h). Few, if any, blasts remained by 48 h of coculture. The ability to suppress an ac tivated immune response permanently, without affecting nonactivated, bystan der lymphocytes, holds promise that LSM, or their cellular products, could be used for immunotherapy of autoimmune diseases such as myasthenia gravis. (C) 1999 Academic Press.