In Vitro Activation of Human γ/δT Cells by Bacteria: Evidence for Specific Interleukin Secretion and Target Cell Lysis

Abstract

Nontoxigenic bacteria can be roughly divided into two major groups: extracellular bacteria, which primarily replicate in the extracellular milieu, the host responding to them with a purulent reaction; and intracellular bacteria, which primarily multiply inside host cells, the host response being characterized by a granulomatous reaction (Hahn and Kaufmann 1981). Protective immunity against extracellular bacteria is mediated by protective antibodies which facilitate bacterial uptake and subsequent killing by professional phagocytes. Thus, the role of T cells in immunity to extracellular bacteria is thought to be restricted to their function as helpers in the generation of antibody-secreting B cells. This group of pathogens includes streptococci and staphylococci. In contrast, protective immunity against intracellular bacteria is mediated by T lymphocytes which alter macrophage functions. It is supposed that macrophage activation through interleukins produced by helper T cells, and lysis of infected macrophages by cytotoxic T cells, both participate in an effective immune response to intracellular bacteria. This group of pathogens includes Listeria monocytogenes and the pathogenic mycobacteria, Mycobacterium tuberculosis and M. leprae. Such immune responses (help or cytotoxicity) have been attributed to the major T cell population expressing a T cell receptor (TCR) composed of α- and ß-chains.