Exogenous antigens refer to the antigens that enter the body of the organism from the outside while endogenous antigens refer to the antigens produced from within the cell as a part of normal cell metabolism or when the cell is infected by bacteria or viruses.
Examples
viral proteins produced during viral replication;
proteins produced by intracellular bacteria such as Rickettsias and Chlamydias during their replication;
proteins that have escaped into the cytosol from the phagosome of phagocytes such as antigen-presenting cells;
