Bacterial and parasitic infections
Phagocytic cells, notably macrophages (MØ), present antigenic peptides from the degraded bacteria to Th1 and Th2 cells through MHC class II (MHC II) molecules. This also happens in protozoal infections and is in contrast to what happens in viral infections or in other situations where antigenic peptides are generated de novo by synthesis in the antigen-presenting cells; see viral infections and cancers.
