In vivo apoptosis of diabetogenic T cells in NOD mice by IFN-γ/TNF-α

Abstract

Immunization with mycobacterial preparation such as Bacille Calmette-Guérin (BCG) or complete Freund's adjuvant (CFA) prevents the onset and recurrence of type 1 diabetes in non-obese diabetic (NOD) mice. In this study, we explored the mechanism underlying the down-regulation of diabetogenic T cells by BCG treatment. We found that the potential of splenocytes from BCG-immunized diabetic NOD mice to adoptively transfer diabetes was significantly impaired. BCG immunization sequentially induced the production of TNF-α, IFN-γ and IL-4 by splenocytes, increased the expression of Fashigh (Apo-1/CD95), Fas ligand (FasL, CD95L) and TNF receptor (TNFR) on T cells leading to T cell apoptosis. The primary role of IFN-γ and TNF-α in BCG-immunotherapy was demonstrated by (i) reversing the immune regulatory effect of BCG by in vivo treatment with neutralizing anti-cytokine antibodies, (ii) inducing effect similar to BCG by treatment with these cytokines. We show that Fas and TNF are two pathways in BCG-induced apoptosis of diabetogenic T cells, since in vitro blocking FasL or TNFR1 with antibody reduced T cell apoptosis and increased T cell proliferative response. In addition, TNF-α and agonistic anti-Fas antibody had a synergistic effect on the in vitro apoptosis of diabetogenic T cells. Our results suggest that BCG down-regulates destructive autoimmunity by TNF-α/IFN-γ -induced apoptosis of diabetogenic T cells through both Fas and TNF pathways. These studies provide a novel mechanism for blocking disease recurrence and immune modulating effect of BCG immunization in type 1 diabetes. © 2004 The Japanese Society for Immunology.