Table 1.
Characteristics of innate lymphoid cell (ILC) populations in humans.
| ILC1 | ILC2 | ILC3 | LTi | ILCreg | NK | ||
|---|---|---|---|---|---|---|---|
| Function | Antimicrobial defense (intracellular microbes) (1) | Allergies, parasite elimination (3) | Innate immunity against fungi and extracellular microbes (1, 3) | Mesenchymal organizer for SLN in embryonic development (3) | Resolution of innate intestinal inflammation (4) | Antitumor surveillance, antimicrobial defense (intracellular pathogens and viruses) (5) | |
| Phenotype | Variable depending on tissue residency | CRTH2+ST2+CD161+ (6, 7) | Controversial Lin− (CD56+/−)CD127+CRTH2−CD117+NKp44+/− (8, 9) | Controversial NRP1 (10) | Lin−CD45+CD127+IL10+ (11) | CD56+CD16+/− | |
| Transcription factor | T-bet (1, 3, 12) | GATA3, RORα (1, 3, 13) | RORγt (1, 3) | RORγt (3) | – | T-bet, EOMES (3, 5, 12, 14, 15) | |
| Inducing cytokines | IL-12 (16) | IL-33, IL-25, TSLP (1, 7, 17) | IL-7, IL-23, IL-1β (3, 18) | – | – | IL-15 (3, 5, 12, 14, 15) | |
| Produced cytokines | IFN-γ (1, 3, 12) | IL-4, IL-5, IL-13 (1, 7, 17) | IL-22, IL-17A, GM-CSF, IFN-γ, TNF-α (3, 18) | IL-22, IL-17, GM-CSF, TNF-α and TNF-β, IL-8 (10) | IL-10, TGF-β (11) | IFN-γ, perforin granzyme B | |
| Regulated tissues | Main | Tonsils, gut, lung, liver, adipose tissue, skin, LN, spleen (6, 19–21) | Peripheral blood, skin, lungs, adipose tissue (6, 7, 22) | Mucosal tissues (gut) (6, 16) | Lymphoid organs | ILCreg: intestine (11), kidney (23); follicular ILCreg: tonsils, LN (24) | Blood |
| Possible | Peripheral/cord blood (6) | Liver, LN, spleen, adenoids (6) | Blood, spleen, LN, tonsils, intestine, skin and lung (6) | – | – | ||
| Association with systemic autoimmune diseases | Increased in Ssc, SLE, active AAV (25–31), Increased or decreased in RA (32, 33) | Increased in SSc and RA (33–35), Decreased in AAV and SLE (27–29, 31) | Increased (29) or decreased (27, 28) in SLE, Increased (36) or decreased (33) in RA Decreased in AAV (31) | Decreased in RA (32) | |||
IL, interleukin; NRP1, neuropilin1; T-bet, T box expressed in T cells; GATA 3, Trans-acting T-cell-specific transcription factor GATA3; RORγT, retinoid acid-related orphan receptor γ T; RORα, retinoid acid-related orphan receptor α; LN, lymph node; CRTH2, chemoattractant-homologous receptor expressed on Th2 cells; Ssc, systemic sclerosis; SLE, systemic lupus erythematosus; AAV, ANCA-associated vasculitis; RA, rheumatoid arthritis.