Role of perforin in controlling B-cell hyperactivity and humoral autoimmunity.

To determine the role of perforin-mediated cytotoxic T lymphocyte (CTL) effector function in immune regulation, we studied a well-characterized mouse model of graft-versus-host disease (GVHD). Induction of acute GVHD using perforin-deficient donor T cells (pfp --> F1) initially resulted in features of acute GVHD, e.g., engraftment of both donor CD4(+) and CD8(+) T cells, upregulation of Fas and Fast, production of antihost CTL, and secretion of both Th1 and Th2 cytokines. Despite fully functional Fast activity, pfp donor cells failed to totally eliminate host B cells, and, by 4 weeks of disease, cytokine production in pfp --> F1 mice had polarized to a Th2 response. Pfp --> F1 mice eventually developed features of chronic GVHD, such as increased numbers of B cells, persistence of donor CD4 T cells, autoantibody production, and lupuslike renal disease. We conclude that in the setting of B- and T-cell activation, perforin plays an important immunoregulatory role in the prevention of humoral autoimmunity through the elimination of both autoreactive B cells and ag-specific T cells. Moreover, an ineffective initial CTL response can evolve into a persistent antibody-mediated response and, with it, the potential for sustained humoral autoimmunity.