Cytotoxic T lymphocytes, or CTLs, are generated by immune activation of T cytotoxic (TC) cells. These effector cells have lytic capability and are critical in the recognition and elimination of altered self-cells (e.g., virus-infected cells and tumor cells) and in graft-rejection reactions. In general, CTLs are CD8+ and are therefore class I MHC restricted, although in rare instances CD4+ class II-restricted T cells have been shown to function as CTLs. Since virtually all nucleated cells in the body express class I MHC molecules, CTLs can recognize and eliminate almost any altered body cell.
The CTL-mediated immune response can be divided into two phases, reflecting different aspects of the response. The first phase activates and differentiates naive TC cells into functional effector CTLs. In the second phase, effector CTLs recognize antigen-class I MHC complexes on specific target cells, which leads them to destroy the target cells.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.