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Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells.. A cytotoxic T cell (also known as T C, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8 + T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pathogens such as viruses or bacteria, or ...
Within the scientific discipline of toxicology, Cytotoxic T lymphocytes (CTLs) are generated by immune activation of cytotoxic T cells (T c cells). They are generally CD8 +, which makes them MHC class I restricted. CTLs are able to eliminate most cells in the body since most nucleated cells express class I MHC molecules.
After vaccine induced activation, dendritic cells are able to migrate to lymph nodes and activate CD4+ T helper cells as well as cross prime CD8+ T cytotoxic cells. This mass generation of activated tumor specific CD8+ T cells increases anti-tumor immunity, and is also able to overcome many of the immune suppressive effects of tumor cells. [10]
Markers of T cell activation include CD69, CD71 and CD25 (also a marker for Treg cells), and HLA-DR (a marker of human T cell activation). CTLA-4 expression is also up-regulated on activated T cells, which in turn outcompetes CD28 for binding to the B7 proteins. This is a checkpoint mechanism to prevent over activation of the T cell.
Only licensed dendritic cells are able to activate cytotoxic T cells. T cell licensing of dendritic cells is key for activation of cytotoxic T cells for many pathogens, although the extent to which T cell help is needed may vary. [14] In MHC class I and class II molecules, only certain epitopes of an internalized peptide can be presented.
Priming of naïve T cells requires dendritic cell antigen presentation. Priming of naive CD8 T cells generates cytotoxic T cells capable of directly killing pathogen-infected cells. CD4 cells develop into a diverse array of effector cell types depending on the nature of the signals they receive during priming.
As well as in CD8+ cytotoxic T cells, APCs need pMHC-II and additional costimulatory signals to fully activate naive T helper cells. Alternative pathway of endogenous antigen processing and presentation over MHC-II molecules exists in medullary thymic epithelial cells (mTEC) via the process of autophagy.
Activated effector T cells can be placed into three functioning classes, detecting peptide antigens originating from various types of pathogen: The first class being 1) Cytotoxic T cells, which kill infected target cells by apoptosis without using cytokines, 2) T h 1 cells, which primarily function to activate macrophages, and 3) T h 2 cells ...