Alternative antigen processing pathways in anti-infective immunity

Proteinaceous and nonproteinaceous antigens from exogenous microorganisms can be processed by the host for MHC class I restricted presentation to T cells. Macrophages, B cells, mast cells and dendritic cells are antigen-presenting cells that process such exogenous antigens through multiple pathways before MHC-restricted epitope presentation. New conceptual frameworks are emerging regarding the processing and presentation to T cells of peptide or nonpeptide epitopes from bacteria in the context of conventional MHC class I molecules, nonconventional MHC class I molecules, or CD1 molecules. Animal experiments have demonstrated that these pathways are of central importance for generating protective antibacterial T cell responses. These findings form the basis for new vaccine designs that specifically target MHC class I restricted T cell reactivity.