Table 1.

Classification of human innate lymphoid cells [3,9,21].

ILC Subtypes	NK-cell	ILC1	ILC2	ILC3	LTi (Lymphoid Tissue Inducer)
Cytokine production	TH1 cell-associated cytokines: IFNγ		TH2 cell-associated cytokines: IL5, IL13, IL6, IL9	TH17 cell-associated cytokines: IL17, IL22 g	TH17 cell-associated cytokines: IL17, IL22: mainly IL17A+
Phenotype	CD25−/+ a, CD56+, CD117−, CD127−/+, CD161−/+, NKp44−/+ b, NKp46+, ICOS+/− CRTH2−, IL1R−, IL23R−, IL12Rβ2+, ST2−, IL17RB−	CD25+/−, CD56−, CD117−, CD127+ d, CD161+/−, NKp44−, NKp46−, ICOS+, CRTH2−, IL1R+, IL23R−, IL12Rβ2+, ST2−, IL17RB−	CD25+, CD56−, CD117+/−, CD127+, CD161+, NKp44−, NKp46−, ICOS+, CRTH2+, IL1R+, IL23R ND f, IL12Rβ2−, ST2+, IL17RB+	CD25−/+, CD56+/−, CD117+, CD127+, CD161+ c, NKp44+ c, NKp44− e, NKp46+, ICOS+ c, CRTH2 c, IL1R+ c, IL23R+ c, IL12Rβ2− c, ST2− c, IL17RB− c	CD25+/−, CD56−, CD117+, CD127+, CD161+/−, NKp44−, NKp46−, ICOS ND f, CRTH2−, IL1R+, IL23R+, IL12Rβ2−, STR2, IL17RB−
Differentiation of ILCs	T-bet+, Eomes+, RORγt−, GATA3−, AhR−	T-bet+, Eomes−/+, RORγt−, GATA3−, AhR−	T-bet−, Eomes−, RORγt−, RORα+, GATA3+, AhR+	T-bet−, Eomes−, RORγt+, GATA3−, AhR+	T-bet−, Eomes−, RORγt+, GATA3−, AhR+
Function	Pro-inflammatory against bacteria and intracellular viruses		Defence against helmintic infections	Maintain homeostasis, immune tolerance, defence against fungal infections	LTi role in formation of secondary lymphoid organs during embryogenesis

^a Expressed in activated CD56^bright NK-cells. ^b Expressed in activated NK-cells. ^c In NCR+ ILC3, ^d except for intraepithelial ILC1 cells. ^e In NCR- ILC3. ^f Not determined. ^g NCR+ ILC3 cells primarily express IL22 but less IL17 whilst the reverse is true of NCR- ILC3.