Fig. 2.

Cell intrinsic recognition. Dendritic cells directly infected by viruses recognize pathogen-associated molecular patterns(PAMPs) (blue) within the cytosol via RIG-I like receptors (RLRs). Cytosolic viral proteins (red) are processed and presented on MHC class I (via the conventional ER pathway) or major histocompatability complex (MHC) class II (via autophagy). RLR signaling leads to the induction of costimulatory molecules and cytokines necessary for activation and differentiation of T lymphocytes. How the origin of antigen is established in this case is unclear. In the case of MHC class I pathway, this may depend on the abundance of viral antigens. In the case of MHC class II pathway, it may depend on targeting of viral antigens by the autophagy machinery.