Fig.  2

NK cell development. In mice, common lymphoid progenitor (CLP) produces common ILC precursor, CILCP). CILCP can produce NK cells and helper-like ILCs. There are at least five other stages in NK cell development from CILCP: NK progenitor cells (NKP), refined-NKP (rNKP), CD27⁺CD11b⁻NK, CD27⁺CD11b⁺NK and CD27⁻CD11b⁺ NK. In humans, after CILCP is developed from CLP, NK-restricted NKP will be developed from the latter. NKs is characterized by expressing CD122, losing CD34 and CD127. The expression of T-bet and Eomes is needed for further differentiation into functional NK cells. The expression of CD56 can divide NK cells into two subgroups: CD56^dim and CD56^bright. The two subsets express activated surface receptors NKp46 and NKp80. CD56⁺ NK cells can differentiate into CD56⁻ NK cells by expressing CD16, PEN5 and CD57