Cellular immunity: the final paradigm?
Cytotoxic T lymphocyte activation and most probably tolerance induction, is dependent on antigen presentation by a specialized group of cells, APC, including macrophages, dendritic cells and B cells. Since T lymphocytes are, at least, the majority of the time MHC molecule class-specific, CD8+ T cells require antigen presented by MHC class I molecules. MHC class I molecules are, however, restricted to presenting endogenously produced antigenic peptides. Most threats to the organism are of exogenous origin and do not uniformly affect all or even most of the cells of an organism. This precludes the likelihood that any number of APC would be involved in every threatening situation, which raises the important question of how T lymphocytes are indeed activated, especially CD8+ T cells (MHC class I restricted).
Attfield
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DC
Department of Pathology, University of Pittsburgh, Pennsylvania, USA. Atfield+@pitt.edu
D000818:Animals; D006801:Humans; D007111:Immunity, Cellular / Q000276:immunology* / Q000502:physiology