IMMUNOLOGY

Detailed explanation-1: -T cells have dual specificity, so they recognize both self-major histocompatibility complex molecules (MHC I or MHC II) and peptide antigens displayed by those MHC molecules.

Detailed explanation-2: -T cells can detect the presence of an intracellular pathogen because infected cells display on their surface peptide fragments derived from the pathogen’s proteins. These foreign peptides are delivered to the cell surface by specialized host-cell glycoproteins.

Detailed explanation-3: -T cell recognition of foreign peptide antigen and tolerance to self peptides is key to the proper function of the immune system. Usually, in the thymus T cells that recognize self MHC + self peptides are deleted and those with the potential to recognize self MHC + foreign peptides are selected to mature.

Detailed explanation-4: -When cytotoxic T cells and some helper T cells are activated by antigen to become effector cells, they secrete the cytokine interferon- (IFN-), which greatly enhances anti-viral responses. The IFN- acts on infected cells in two ways.

Detailed explanation-5: -Armed effector cytotoxic CD8 T cells are essential in host defense against pathogens that live in the cytosol, the commonest of which are viruses. These cytotoxic T cells can kill any cell harboring such pathogens by recognizing foreign peptides that are transported to the cell surface bound to MHC class I molecules.