Recent developments in MHC-class-I-mediated antigen presentation.

Defective ribosomal products provide an important supply of endogenous peptides for entry into the classic MHC class I antigen presentation pathway. The recruitment of endoplasmic reticulum membrane during phagosome biogenesis allows exogenous antigens to be translocated into the cytosol as well as providing access to the class I peptide transport and loading machinery. This combination of features provides a mechanism for cross-presentation by specialised antigen presenting cells. Recent studies have shed new light on these pathways and have also described the emerging K3 family of viral ubiquitin E3 ligases, which constitutively ubiquitinate and degrade MHC class I molecules and other immunoreceptors.