The structure and function of MHC. (IMAGE)
Caption
The structure and function of MHC. (A) MHC-II antigen presentation pathway. This pathway illustrates the process by which exogenous antigens (e.g., TAAs, apoptotic bodies, or cellular debris) are internalized by APCs through phagocytosis. These antigens are subsequently processed within endosomal compartments, where the antigens are degraded into peptides. The peptides are then loaded onto MHC-II molecules, which are trafficked to the cell surface. Peptide–MHC-II are recognized by CD4+ T cells via the TCR at the membrane, leading to activation and cytokine secretion. This pathway is primarily involved in initiating and modulating Th cell responses. (B) MHC-I antigen presentation pathway. This pathway shows the presentation of endogenous antigens (e.g., cytosolic proteins from tumor cells or intracellular pathogens). These proteins are degraded by proteasomes into peptide fragments, which are then translocated into the endoplasmic reticulum where the proteins are loaded onto MHC-I molecules. The peptide–MHC-I complexes are transported to the cell surface, where the peptide–MHC-I complexes are recognized by CD8+ CTLs via the TCRs. This recognition enables CTLs to target and eliminate infected or malignant cells. pAPCs may also cross-present exogenous antigens via the MHC-I pathway to activate naïve CD8+ T cells. APC: antigen-presenting cell; CTL: cytotoxic T lymphocyte; MHC-I: major histocompatibility complex class I; MHC-II: major histocompatibility complex class II; pAPC: professional antigen-presenting cell; TAA, tumor-associated antigen; TCR, T cell receptor. The figure was created by Figdraw.
Credit
Cancer Biology & Medicine
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