Subpopulations of Cytotoxic T Lymphocytes with Different Cytotoxic Mechanisms

Abstract

Subpopulations of T lymphocytes have been identified based on (1) expression of CD4 or CD8 accessory molecules on the cell surface [CD4+ cells generally recognize antigen (Ag) presented in the context of class II major histocompatibility complex (MHC) molecules, while CD8+ cells generally recognize Ag presented in the context of class I MHC molecules], (2) the structure of their T-cell receptor (TCR) (α/β versus γ/δ), (3) the array of lymphokines that the cells produce, and (4) functional characteristics. T-cell functions in heterogeneous populations of T cells appeared to be correlated with the expression of CD4 or CD8 molecules on the T-cell surface. Thus, T-cell-mediated cytotoxicity was associated with CD8+ T cells, while T-cell-mediated helper functions appear to reside primarily in the CD4+ T cells. However, it is now generally accepted that cytotoxic activity is not restricted to CD8+ T cells. The lytic activity of cells bearing the γ/δ TCR is well established. The extent of expression of cytotoxicity among the members of CD4+ subsets is still controversial. In this review, we summarize recent observations regarding the expression of cytotoxic activity among T-cell subsets bearing CD4 molecules. In addition, we explore the growing body of evidence indicating that cytotoxic activity expressed by lymphocytes within different T-cell subpopulations may be accomplished through distinct and independent mechanisms.KeywordsMajor Histocompatibility ComplexMajor Histocompatibility Complex MoleculeSerine EsterasePercent Specific LysisInduce Target CellThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.