What triggers antigen presentation by MHC Class I proteins?

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Multiple Choice

What triggers antigen presentation by MHC Class I proteins?

Antigen presentation by MHC Class I highlights peptides that come from proteins made inside the cell, so cytotoxic T cells (CD8+) can check for signs of infection or abnormal proteins. When a cell is infected by a virus or by intracellular bacteria, viral or bacterial proteins are produced in the cytosol and chopped into small peptides by the proteasome. These peptides are transported into the endoplasmic reticulum by TAP, loaded onto MHC Class I molecules, and then displayed on the cell surface. This lets CD8+ T cells recognize and kill the infected cell, stopping the infection. Other scenarios don’t fit this pathway. Allergic reactions involve IgE and mast cells rather than endogenous peptide presentation; mechanical injury is tissue damage without engaging the endogenous peptide processing route; extracellular toxins are typically handled via MHC Class II in professional antigen-presenting cells after phagocytosis. So the trigger for MHC Class I presentation is intracellular infection.

Antigen presentation by MHC Class I highlights peptides that come from proteins made inside the cell, so cytotoxic T cells (CD8+) can check for signs of infection or abnormal proteins. When a cell is infected by a virus or by intracellular bacteria, viral or bacterial proteins are produced in the cytosol and chopped into small peptides by the proteasome. These peptides are transported into the endoplasmic reticulum by TAP, loaded onto MHC Class I molecules, and then displayed on the cell surface. This lets CD8+ T cells recognize and kill the infected cell, stopping the infection.

Other scenarios don’t fit this pathway. Allergic reactions involve IgE and mast cells rather than endogenous peptide presentation; mechanical injury is tissue damage without engaging the endogenous peptide processing route; extracellular toxins are typically handled via MHC Class II in professional antigen-presenting cells after phagocytosis. So the trigger for MHC Class I presentation is intracellular infection.

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