Effector cytotoxic cells

Immune Defense. Figure 2 Cytokines involved in the development of adaptive immune responses in secondary lympoid tissues such as the lymph nodes or spleen. Abbreviations B B-lymphocyte, IFN interferon, Ig immunoglobulin, IL interleukin, NK natural killer cell, TE T-effector (cytotoxic) lymphocyte, TH T-helper lymphocyte... 

Evans, D.L. and L. Jaso-Friedmann. Nonspecific cytotoxic cells as effectors of immunity in fish. Annu. Rev. Fish Dis. 1 109-121, 1992. 

T lymphocytes may be separated into two major functional subpopulations having either regulatory or effector function. Regulatory cells represent about 70% of all T lymphocytes in the peripheral circulation and are separated into helper cells and suppressor cells. The remaining T cells have an effector function and are known as cytotoxic cells. 

A. Overview The innate immune system initiates the defense against pathogens and antigenic insult. It involves the concerted actions of complement components, lysozyme, macrophages, and neutrophils. If the innate response is inadequate, the adaptive immune response is mobilized. This culminates in the activation of T lymphocytes, the effectors of cell-mediated immunity and the production of antibodies, by activated B lymphocytes, the effectors of humoral immunity. The cell types involved in immune responses can be identified by specific cell surface components or clusters of differentiation (CDs). For example, T helper cells bear the CD4 protein complex, whereas cytotoxic T lymphocytes express the CDS protein complex. Clusters of differentiation also can be used to characterize other types of hematopoietic cells, including precursors of granulocytes, megakaryocytes, and erythrocytes (Chapter 33). 

A particular monoclonal antibody specific for the influenza virus haemag-glutinin molecule is capable of blocking virus-specific cytotoxic T cells in an in vitro assay.The binding appears to be in the context of the histocompatibility antigen 11-20 but not of H-2K . Another monoclonal antibody that has been isolated is capable of blocking both sets of HA-specific effector T cells. 

Fig. 7.1. Principles of tumor cell kill by antibodies bispecific antibody-mediating effector-tumor cell interaction, naked antibody mediating antibody dependent cellular cytotoxicity...

This class of lymphocytes differentiates from immuno-logically incompetent hematopoietic stem cells of the bone marrow within the thymus - hence, the name thymus-dependent (T-) lymphocytes. Two major subclasses develop simultaneously, T-helper lymphocytes (Th) and cytotoxic effector lymphocytes (Tc). The cytotoxic T-lymphocytes (carrying on the surface the differentiation marker CD8) destroy cells, which cany their cognate antigen bound to MHC class I molecules on the surface by inducing apoptosis. From an evolutionary point of view Tc cells appear to have developed predominantly to cope with vims infections. As vituses can only replicate within cells, Tc eliminate them by destroying their producers. 

Several cytokines are in clinical use that support immune responses, such as IL-2, DFNs, or colony-stimulating factors. IL-2 supports the proliferation and effector ftmction of T-lymphocytes in immune compromised patients such as after prolonged dialysis or HIV infection. IFNs support antiviral responses or antitumoral activities of phagocytes, NK cells, and cytotoxic T-lymphocytes. Colony-stimulatory factors enforce the formation of mature blood cells from progenitor cells, e.g., after chemo- or radiotherapy (G-CSF to generate neutrophils, TPO to generate platelets, EPO to generate erythrocytes). 

Two main apoptotic pathways have been identified in mammalian cells the extrinsic pathway that is activated by the binding of ligands to cell-surface death receptors, and the intrinsic pathway that involves the mitochondrial release of cytochrome cP The activation of extrinsic and intrinsic apoptotic pathways promotes the cleavage into the active form of the pro-caspase-8 and pro-caspase-9, respectively, that mainly determine the activation of effector caspase-3. ° The intrinsic pathway is the main apoptotic pathway activated by chemotherapeutic drugs, while the cytotoxic drug-induced activation of the extrinsic pathway is a more controversial issue. ... 

Helper T cells (CD4+) are the great communicators of the immune response. Once activated, they proliferate and secrete cytokines that regulate effector cell function. Some helper T cells secrete cytokines that recruit cytotoxic T cells, B cells, or APCs, whereas others secrete cytokines that turn off the immune response once an antigen has been destroyed. 

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