For a T cell to enter an inflamed or infected tissue, it must first adhere to the endothelium of a blood vessel at that site, and cross the vessel wall by extravasation. Adhesion and extravasation are mediated by the interaction of adhesion molecules expressed on the endothelial cells with cell surface receptors (integrins) on the T cells. An important endothelial adhesion molecule is the intercellular adhesion molecule-1 (ICAM-1), a cell-surface glycoprotein and member of the immunoglobulin gene superfamily. Although
infected host cell antigen peptide
Fig. 5.4 Activation of T lymphocytes by antigen presentation. See text for details.
weakly expressed in non-stimulated cells, ICAM-1 expression is strongly increased by pro-inflammatory cytokines such as IL-ip, IFN-y and TNF-a, as well as by bacterial lipopolysaccharides and phorbol esters. ICAM-1 interacts with lymphocyte-function-associated antigen-1 (LFA-1), a member of the P2 subfamily of integrins, which is constitutively expressed by lymphocytes and other cells of the immune system. In addition to its role in adhesion and extravasation of T cells, the LFA-1/ICAM-1 adhesion system is important for antigen presentation (Altmann et al., 1989).
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