Table 1.
IL‐17 cytokines and their receptors, cellular sources, target cells and functions
| IL‐17 cytokine | IL‐17R subunits | Sources | Target cells | Role in host defence and health | Role in disease |
|---|---|---|---|---|---|
| IL‐17A homodimer |
RA+RD [29] |
Th17 cells [5, 6], Tc17 cells [8], γδ T cells [9, 10, 11], iNKT cells [9], ILC3 [12] | Keratinocytes, epithelial cells, fibroblasts [38] | Defence against extracellular bacterial and fungal infections, barrier function, wound healing, microbiome [38] | Pathogenic in chronic inflammation, autoimmunity and some cancers [38] |
| IL‐17F homodimer |
RA+RC [31] RC+RC [30] |
||||
| IL‐17A+F heterodimer | RA+RC [28, 31] | Role of IL‐17A+F unclear | Role of IL‐17A+F unclear | ||
| IL‐17C homodimer | RA+RE [31] | Keratinocytes, epithelial cells, cutaneous neurones [16, 17, 18, 19, 38] | Autocrine effects on keratinocytes, epithelial cells, neurones [38] | Microbial defence, barrier maintenance, response to epithelial injury, cutaneous neuroprotection [38] | Pathogenic in inflammatory skin diseases including psoriasis [19], atopic dermatitis [112], HS [111] |
| IL‐17E homodimer (IL‐25) | RA+RB [31] | Keratinocytes, endothelial cells, epithelial cells, Th2 cells, macrophages, myeloid cells, ILC2 [20] [38] | Epithelial cells, fibroblasts, endothelial cells, Th2 cells, Th9 cells, iNKT cells, ILC2 [20] | Defence against helminths, promotes Th2 cell‐mediated immunity [38] | Pathogenic in allergy [20] and psoriasis [21] |
| IL‐17B homodimer | RB+? [31] | Neutrophils, B cells, neurons, stromal cells, epithelial cells, chondrocytes [22, 24] | Epithelial cells, fibroblasts, macrophages [24, 124] | Protective against Citrobacter rodentium infection [24] | Pathogenic in inflammatory arthritis [124], gastric and breast cancers [22], lung fibrosis [23], protective against colitis and asthma [24] |
| IL‐17D homodimer | Unknown | Skeletal muscle, brain, adipose, heart and lung tissue [22] | Endothelial cells [22], DC [25], macrophages [26] | Protective against viral infection and tumours [22] | Pathogenic in sepsis [26], pathogenic role in certain intracellular infections [25] |
IL = interleukin; Th17 = T helper type 17; iNK T = invariant natural killer T cells; ILC = innate lymphoid cells; DC = dendritic cells; HS = hidradenitis suppurativa.