Antigen presentation--recent developments.

Antigen presentation is principally a function of MHC molecules, assisted by a number of adhesion and co-stimulatory molecules not immediately involved in antigen handling. Each MHC molecule, class I or class II, presents peptides derived from self or foreign proteins according to individual rules which have been elucidated in detail for several dozens of MHC molecules. How such peptides are produced by the antigen processing devices in a cell is less well understood; for class I-restricted processing, proteasomes, TAP molecules and probably chaperones are key players whereas the invariant chain, DM molecules, and a number of proteins are central to class II loading. Currently of special interest are alternative class I-loading pathways, nonclassical MHC molecules, the way NK cells recognize their targets, and the use of MHC peptide specificities for applications in immune therapy.