A proposed 3-stage model for the development and differentiation of γδ-17 cells. In the first stage, functionally uncommitted γδ thymocytes commit to the γδ-17 lineage and begin to express RORγt. These RORγT+ γδ thymocytes are referred to as γδ-17 precursors. In the next stage, these γδ-17 precursors mature by acquiring expression of CCR6 and interleukin (IL)-23R and then emigrate to the periphery. At the last stage, peripheral γδ-17 cells differentiate into cytokine-producing effectors. See text for more details. Blk, B lymphoid kinase; LTβR, lymphotoxin-β receptor; PGIR, Prostaglandin I2 receptor.