Suppressive activity of long-term myelin basic protein-specific SJL T cell lines

Myelin basic protein (MBP)-specific T cell lines derived from SJL mice lose the ability to transfer adoptively experimental allergic encephalomyelitis (EAE) after 5-6 restimulations with antigen in vitro. In order to test whether such lines were suppressive, non-encephalitogenic T cell lines were co-cultured with a freshly derived encephalitogenic T cell line. Following co-culture in the presence of MBP and irradiated syngeneic spleen cells the mixture was transferred adoptively to syngeneic recipients. Severe EAE was observed in recipients of the encephalitogenic cell line alone but not in animals which received the co-culture. A co-culture period was required as mixing the encephalitogenic and non-encephalitogenic T cell lines just prior to transfer was without effect. Not all non-encephalitogenic cell lines were found to be suppressive. Culture fluids from the suppressive, but not the non-suppressive lines were found to inhibit MBP-driven proliferation of T cell clones and encephalitogenic lines in vitro. Nineteen of 55 MBP-specific T cell clones derived from suppressive lines were found to elaborate the suppressive supernatant activity. The suppressive effect was not antigen-specific since the same culture supernatants inhibited proliferation of an ovalbumin-specific SJL T cell clone. The suppressive effect became apparent only after T cell lines had lost encephalitogenicity and was not mediated by tumor necrosis factor, lymphotoxin or prostaglandin.