Figure 2: CD4 T cell effector subsets A CD4 T cell (Th) can differentiate into unique effector subsets determined in part by the cytokine milieu that is present when the cell encounters antigen. Effector subsets are classified by the dominant transcription factor in concert with the cytokines that they express. Th cells that develop optimal cytotoxic activity (ThCTL) may be distinct from the other identified effector subtypes.