Longitudinal samples were taken from the TI and SC of a subset of patients who underwent repeat endoscopy (CD: em n /em ?=?13; UC: em n /em ?=?4). neutrophil activity. Conclusion The NCR\ ILC3: GM\CSF: neutrophil axis could contribute to the development of IBD. and and and and and was measured at the indicated time point. Data are normalised to (Physique?5h, i), and mRNAs (Supplementary physique 7g) from neutrophils, and the level of mRNA was also higher in colonoscopic biopsies of patients with IBD (Supplementary physique 7h). Since these cytokines are not only well\known Paris saponin VII stimulating factors of ILC3s but also critical for the development of IBD, the crosstalk between NCR\ ILC3s and neutrophils may be involved in the development of IBD. Blockade of GM\CSF and neutrophils reduces intestinal inflammation in DSS\induced colitis Next, we injected anti\GM\CSF antibodies (Ab) into DSS\treated WT mice to evaluate the role of GM\CSF in the development of colitis (Physique?6a). Treatment with anti\GM\CSF Ab resulted in the restoration of shortened colons (Physique?6b, c) and collapsed epithelial cells (Physique?6f, g). To exclude the role of adaptive immune cells, we confirmed these results in co\culture experiments, we found that GM\CSF\generating NCR\ ILC3s can induce neutrophil activation. Furthermore, blockade of GM\CSF ameliorated DSS\induced colitis by inhibiting the activation of neutrophils mRNA. TGF\ signalling was recently proposed to induce the conversion of NCR+ ILC3s to NCR\ ILC3s 30 ; however, the source of TGF\ and the signalling pathway involved remain unknown. Changes from homeostatic NCR+ ILC3s to pathogenic NCR\ ILCs might be involved in the development of colitis. Therefore, more detailed research on how these reversible NCR+ ILC3s and NCR\ Paris saponin VII ILC3s interact with surrounding inflammatory cells such as neutrophils will be of interest. The functions of GM\CSF on intestinal immune cells are quite complex. GM\CSF can exhibit protective functions in the intestine. For example, neutralising anti\GM\CSF autoantibodies ZNF538 are increased in IBD, 31 and GM\CSF KO mice are less susceptible to DSS\induced colitis. 32 Also, recombinant GM\CSF treatment ameliorates acute DSS\induced colitis. Paris saponin VII 33 From your perspective of ILCs, GM\CSF from ILC3s can maintain gut homeostasis by generating retinoic acid and IL\10 in DCs and macrophages to facilitate tolerance function. 14 However, a recent large\scale clinical trial reported that recombinant GM\CSF (sargramostim) was not effective in inducing clinical mitigation or improvement in patients with active CD. 34 Although GM\CSF has a protective effect, it also acts as an essential mediator of tissue inflammation. 35 , 36 GM\CSF exacerbates colitis by promoting the accumulation of Ly\6C+ inflammatory monocytes 17 , 18 ; namely, NCR+ ILC3s promote inflammation through GM\CSF\induced accumulation of inflammatory monocytes in the anti\CD40 innate colitis model. 18 We also found that GM\CSF production has increased in the colons of DSS\induced colitis mice and colonoscopic biopsies from patients with IBD, although there was a difference in the subset of ILC3s that produce GM\CSF. Here, we showed that GM\CSF\generating NCR\ ILC3s aggravate IBD by activating neutrophils. Neutrophils have long been considered as effector cells in acute and chronic inflammation 37 by secreting significant amounts of pro\inflammatory cytokines 38 and matrix metalloproteases (MMPs). 39 Moreover, inhibition of neutrophil recruitment alleviates DSS\induced colitis. 40 , 41 Therefore, the reciprocal conversation between NCR\ ILC3s and neutrophils may contribute to the pathogenesis of IBD. Up to now, the drugs most widely used to treat CD are corticosteroids; immunosuppressants, such as methotrexate; and thiopurines, such as azathioprine and mercaptopurine; and biological brokers, such as the antitumor necrosis factor (TNF) antibodies infliximab, adalimumab, and certolizumab pegol, and the anti\adhesion agent vedolizumab. 42 Clinical trials have shown that 30% to 50% of IBD patients do not respond to anti\TNF therapy, the most advanced treatment currently available. 43 Therefore, option strategies are required to target the mechanisms underlying the pathogenesis of IBD. This study underscores the importance that ILCs should be considered as a therapeutic target for IBD. For example, brokers targeting IL\23, which can stimulate ILC3s, have been evaluated in clinical trials in patients with CD. These include AMG 139, a human anti\IL\23 antibody.