Overview
Interleukin-17 (primarily IL-17A and IL-17F) is the signature cytokine of Th17 cells. At physiological levels, IL-17 maintains mucosal barrier defense by recruiting neutrophils and inducing antimicrobial peptide production. At pathological levels (Th17/Treg imbalance), IL-17 drives autoimmune tissue destruction — it is the therapeutic target in psoriasis (secukinumab), psoriatic arthritis, and ankylosing spondylitis.
Microbiome Regulation
- Segmented filamentous bacteria (SFB) are the strongest known microbial inducers of IL-17-producing Th17 cells in the gut.
- Dysbiosis-driven SCFA depletion shifts the Th17/Treg balance toward IL-17 excess (see th17 treg balance).
- IL-17 elevation is documented across: Graves' disease [1], Hashimoto's [2], schizophrenia [3], T1D [4], MS, IBD, and psoriasis.
Cross-References
- th17 treg balance — IL-17 as Th17 effector cytokine
- interleukin 6 — IL-6 + TGF-beta drives Th17 (IL-17) differentiation
- tgf beta — required for Th17 differentiation (with IL-6)
- il 10 — anti-inflammatory counterbalance
- immune balance — broader immune equilibrium