IL-2 also stimulates B cells to synthesize antibody. MHC proteins bind and present both “self” and “foreign” peptides. These issues are discussed later. The initial steps in the presentation of an extracellular protein antigen are the binding of the native antigen to an APC and the internalization of the antigen. Antigen Processing Pathways: Feature: MHC Class I: MHC Class II: Function: Allow for sampling of intracellular antigens; Signal that a cell is infected or abnormal; Allow for sampling of extracellular antigens; Signal that pathogens are within the host; Target cell: CD8+ killer T-cells; Rule of 8: (MHC) 1 x (CD) 8 = 8; CD4+ helper T-cells ; Rule of 8: (MHC) 2 x (CD) 4 = 8 Such a mechanism is employed by EBV virus protein Epstein–Barr virus nuclear antigen 1 (EBNA-1) (Levitskaya et al., 1995) and Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen-1 (LANA-1) (Zaldumbide et al., 2007). J. Graham Watson MD, BSc, FRCPE, FRCP, DCH, A. Graham Bird MD, MRCPath, FRCP, in Handbook of Immunological Investigations in Children, 1990. First, the antigen-specific T cells must establish physical contact with the APCs. This intimate APC–CD4 T cell contact is favored by cell adhesion molecules the lymphocyte functional antigen-1 (LFA-1) on the T cells with its corresponding ligands, ICAM-1, ICAM-2 and ICAM-3 on the APCs; and the CD2 molecule with its counter-receptor. Endocytic pathway of antigen processing and presentation: The endocytic pathway processed and present the exogenous Ag. This population also contains cells capable of suppressing immune responses. In this way, virally-infected or transformed cells are killed, thereby limiting their further replication or spread of the pathogen. Indeed this is not only a strategy employed by pathogens, as tumors also manipulate antigen presentation pathways to avoid elimination by the immune system. Bernd Kaspers, Pete Kaiser, in Avian Immunology (Second Edition), 2014. Finally, MHC class I that successfully reaches the cell surface loaded with viral peptide, is also subjected to targeting by viral proteins. We use cookies to help provide and enhance our service and tailor content and ads. Antigen–MHC complexes are recognized on the cell surface by the TCR of CD4+ T cells, which then activate other immune effector cells. 2. Finally to note is that several cytokines from APCs modulate the T cell response during antigen presentation. It is also antiproliferative to keratinocytes and cytotoxic to them at high concentrations. It encompasses antigen uptake, processing, and display together with antigen presenting and co-stimulatory molecules by a specialized group of leukocytes named antigen-presenting cells. Other proteins that interfere with TAP activity include UL49.5 (Koppers-Lalic et al., 2005) and adenovirus E3-19K. Overview of Antigen Processing Pathways. DC achieve this by means of the production of subcellular compartments rich in MHC molecules which fuse with the antigen-rich endocytotic vesicles. ICP47 also induces a conformational change that destabilizes TAP, turning off ATP hydrolysis (but not ATP binding) and subsequently inhibits peptide translocation into the ER (Lacaille and Androlewicz, 1998). Antigen presentation by antigen-presenting cells (APC) to the T-cell receptor (TCR) leads to T-cell activation. Details of the APC–T cell interaction are given in the Antigen-Presenting Cell article which contains a table showing the molecules involved. Whilst much of the molecular machinery which allows DC to present antigen has been described for the chicken (see Chapter 8), this is not of itself sufficient to define an immune surveillance system. BERND KASPERS, ... COLIN BUTTER, in Avian Immunology, 2008. The route of processing for exogenous antigens for MHC class II presentation begins with endocytosis of the antigen.
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