Cd8 cytolytic t lymphocytes (ctl) functions: virally infected cells (major) bacterial infected cells tumor cells graft rejection important that their activity is confined only to target cells some cd4 and some nk cells also have cytolytic activity. Protection against bacterial infection several types of bacteria can reside and replicate within host cells. Salmonella, listeria, myobacteria while this might elicit mhcii/cd4 response in some cells, certain cell types. Lack these proteins and the mhci/cd8 route is the only alternative. Activation of ctl after activation, clonal expansion and expression of cytokines also expression of cytolytic proteins (perforin, granzymes) initial stages are cd4 independent, but cd4 is required eventually mechanism is unclear but maybe . Cross priming if apc"s are not directly infected due to protein fragments that are released from cytolysed infected non-apc"s fragments are taken up and presented by apc"s on mhci to cd8+ cells.