The role of CD8 T cells in adaptive immune responses is well understood. These lymphocytes respond through their T cell receptors to diverse antigens presented by MHC class I molecules by proliferating, secreting cytokines and chemokines, and directly lysing infected cells. Recently, a role for CD8 T cells in the innate immune response has become apparent. Independent of T cell receptor ligation, CD8 T cells can mount a response against pathogens by secreting cytokines and can defend against tumors by directly killing transformed cells. This innate response has been shown to be beneficial in controlling several types of bacterial infections. However, a subset of CD8 T cells that have innate non-antigen-specific capabilities has been implicated in self-reactivity, which could lead to autoimmunity.