Antigen-specific suppressor T lymphocytes (Leu-2a⁺3a^-) in human Schistosomiasis japonica

Immunoregulatory mechanisms in human schistosomiasis japonica were investigated through in vitro T lymphocyte-macrophage co-culture experiments. High responder T lymphocytes responded to the schistosomal adult worm antigen in the presence of HLA-DR-compatible low responder macrophages, whereas low responder T lymphocytes failed to respond to this antigen even in the presence of HLA-DR-compatible high responder macrophages. This observation strongly suggested that T lymphocytes, but not macrophages, controlled the low responsiveness to the schistosomal adult worm antigen. When high responder lymphocytes were challenged with the schistosomal antigen in the presence of low responder T lymphocytes, low responder T lymphocytes caused an antigen-specific suppression, in a dose-dependent manner, of the responsiveness of high responder lymphocytes. The suppressor T lymphocytes were mitomycin C resistant and were positive for Leu-2a, but were negative for Leu-3a. When Leu-2a⁺ T lymphocytes were depleted from low responder T lymphocytes, a vigorous response by the Leu-2a-depleted T lymphocytes (Leu-2a^-3a⁺) to the schistosomal adult worm antigen was observed. By additing back the Leu-2a⁺ T lymphocytes into autologous T lymphocyte subpopulations, the specific response to the adult worm antigen was completely suppressed. These findings clearly demonstrate the existence of Leu-2a⁺3a^- suppressor T lymphocytes that can control low responsiveness to the schistosomal adult worm antigen in man.