Figure 3. Pathways of intracellular pathogen clearance from infected cells by cytotoxic cells. Intracellular pathogen-derived antigens complexed to MHC class I molecules are recognized by CTLs, while NK cells recognize the absence or suppressed levels of MHC class I molecules on infected cells. Activated cytotoxic cells deliver apoptotic signals through Fas ligand and perforin to infected cells. They also secrete cytokines (IFN-gð, TNF-að) and chemokines (Rantes, MIP-1að, MIP-1bð) to inhibit or suppress intracellular pathogen replication.