Role of innate lymphoid cells in chronic colitis during anti-IL-17A therapy

IL-17A is an important cytokine in intestinal inflammation. However, anti-IL-17A therapy does not improve clinical outcomes in patients with Crohn's disease. We aimed to evaluate the role of RORγt⁺ innate lymphoid cells (ILCs) in murine colitis models in the absence of IL-17A. An acute colitis model was induced with either dextran sulfate sodium (DSS) or trinitrobenzenesulfonic acid (TNBS) and a chronic colitis model was induced by CD4⁺CD45RB^hi T cell transfer from either wild-type C57BL/6 or Il17a^-/- mice. An anti-IL-17A antibody, secukinumab, was also used to inhibit IL-17A function in the colitis model. Flow cytometry was performed to analyze the population of RORγt⁺ ILCs in the colonic lamina propria of mice with chronic colitis. Acute intestinal inflammation due to DSS and TNBS was attenuated in IL-17A knockout mice, whereas chronic colitis was not relieved by T cell transfer from Il17a^-/- mice (% of original body weight: wild-type mice vs. Il17a^-/- mice, 81.9% vs. 82.2%; P = 0.922). However, the mean proportion of Lin^-RORγt⁺ lymphocytes was higher after T cell transfer from Il17a^-/- mice than that after T cell transfer from wild-type mice (28.8% vs. 18.5%). The proportion of Lin^-RORγt⁺ was also increased in Rag2^-/- mice that received T cell transfer from wild-type mice when anti-IL-17A antibody was administered (31.7%). Additionally, Il6 and Il22 tended to be highly expressed after T cell transfer from Il17a^-/- mice. In conclusion, RORγt⁺ ILCs may have an important role in the pathogenesis of chronic colitis in the absence of IL-17A. Blocking the function of IL-17A may upregulate Il6 and recruit RORγt⁺ ILCs in chronic colitis, thereby upregulating IL-22 and worsening the clinical outcomes of patients with Crohn's disease.