IL17A and autoimmune disease: In healthy individuals, Th17 cell activation is inhibited by TGF-β, which prevents excessive IL-17 secretion and maintains immune tolerance.171 In contrast, Th17 cell activation is enhanced during pathogen invasion, and IL-17 secretion is increased under the combined effects of TGF-β and IL-6, promoting inflammation.16,175 The disruption of IL-17 production can lead to autoimmune diseases and tissue destruction.