Cellular immune response

Immune reaction mediated by specifically sensitized T lymphocytes. The T cells possess specific antigen receptors on their surface for antigen recognition (T cell receptor associated with the CD3 complex). After antigen contact, clonal expansion, the formation of effector and memory cells occurs. T cells recognize antigens on antigen-presenting cells in the context of molecules of the major histocompatibility complex ( MHC). CD8-positive cells recognize antigens in context with MHC I structures. CD4-positive cells recognize antigens in context with MHC II structures. Activation of CD8-positive cells leads to the formation of cytotoxic cells that can kill the target cell, e.g. in viral infections. Antigen presentation in connection with MHC II structures leads to sensitization and production of effector T cells.

Apoptosis in T-lymphocytes: Activation-induced cell death (AICD) is of great importance for the termination of a T-cell-induced immune response (see immunity below). In cutaneous T-cell lymphomas, "resistance" of AICD plays an etiopathogenetic role.