Tissue destruction resulting from the interaction of cytotoxic T cells and their targets.

In vitro and in vivo-generated cytotoxic T lymphocytes (CTL) specific for major and minor histocompatibility antigens evoked antigen-specific full-thickness skin necrosis when injected intradermally into allogeneic mice in a variety of strain combinations. In addition, CTL-target-cell mixtures injected intradermally into hosts syngeneic to the CTL also evoked destruction of host tissue. These "innocent bystander" reactions were evoked with alloreactive CTL as well as with CTL directed against hapten (TNP)-modified and virus (influenza A)-infected target cells. Unlike the direct reactions, the bystander reactions in histocompatibility-antigen systems occurred in spite of H-2 incompatibility of the CTL, admixed target cells, and the hosts. One explanation for these results, currently under investigation, is that some bystander reactions may occur without MHC restriction. In aggregate, our findings indicate that nonspecific as well as antigen-specific reactions initiated by CTL-target-cell interactions may contribute to tissue destruction in allograft rejection, in severe forms of delayed-type hypersensitivity, and in certain viral infections.