Tcell receptor

Fig. 11.11 Subunit structure of the Tcell receptors. The figure shows the different subunits ofT cell receptors in a highly simplified representation. The stoichiometry of the subunits in the complete receptor is not clear. The aft chains are also known as the Tia/ complex the ye and 3e chains together form the CD3 complex. ARAM antigen recognition activation motif.

Fig. 11.12 Overview of signaling pathways associated with activation of lymphocytes. The triggering signal for activation of T lymphocytes is generally antigen binding to the Tcell receptor. The activated receptor passes the signal on to associated tyrosine kinases like Fyn, Lck and ZAP70. These phospho-rylate the transmembrane protein LAT on cytoplasmic tyrosine residues. The LAT phospho-tyro-sine residues are docking sites for adaptors ( She,...

Autoimmune Disease. Figure 2 Generation of autoreactivity. APC, antigen presenting cell IFN, interferon LPS, lipopolysaccharide MHC, major histocompatibility complex T, T-lymphocyte TCR, Tcell (antigen) receptor TLR, toll like receptors. For details see text. 

An important trigger for apoptosis is known as the Fas system. This is used by cytotoxic Tcells, for example, which eliminate infected cells in this way (top left). Most of the body s cells have Fas receptors (CD 95) on their plasma membrane. If a T cell is activated by contact with an MHC presenting a viral peptide (see p. 296), binding of its Fas ligands occurs on the target cell s Fas receptors. Via the mediator protein FADD ( Fas-associated death domain ), this activates cas-pase-8 inside the cell, setting in motion the apoptotic process. 

T cells are bone marro v-derived lymphocytes. There are six different types of Tcells identified in humans helper T cells (Th), cytotoxic T cells (Tc), memory T cells, regulatory T cells (Treg), natural killer T cells (NKT) and yb T cells. AD types have different roles in the adaptive immune systems and consequentiaUy distinct chemokine receptor expression patterns. 

Memory CD4 and CD8 T cells can be divided in effector and central memory Tcells. Effector memory cells are thought to home to nonlymphoid tissues, whereas the central memory T cells localize more to secondary lymphoid tissue [29]. Although originally distinguished by the expression of CCR7 by the central memory T cells, it is clear that both subsets express CCR7 [29, 34]. However, it is thought that these memory cells can express every appropriate chemokine receptor [29]. 

Campbell, J.J. et al. (2001) Expression of chemokine receptors by lung Tcells from normal and asthmatic subjects, /ouma of Immunology (Baltimore, Md 1950), 166, 2842-2848. 

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