Anti–GM-CSF autoantibodies promote a “pre-diseased” state in Crohn’s Disease

Background & Aims: Anti-GM-CSF autoantibodies (aGMAb) are detected in ileal Crohns Disease (CD) patients. Their induction and mode of action impacting homeostasis during, or prior to disease are not well understood. We aimed to investigate the underlying mechanisms leading to the induction of aGMAb, from functional orientation to recognized epitopes, for their impact on intestinal immune homeostasis and use as predictive biomarker for complicated CD. Methods: Using longitudinally collected sera from active component US personnel, we characterize naturally occurring aGMAb in a subset of CD patients years before disease onset. We employed biochemical, cellular, and transcriptional analysis to uncover a mechanism that governs the impaired immune balance in CD years prior to diagnosis. Results: Neutralizing aGMAb are specific to posttranslational glycosylations on GM-CSF, detectable years prior to diagnosis, and associated with complicated CD at presentation. Glycosylation and production of GM-CSF change in CD patients, altering myeloid homeostasis and destabilizing group 3 innate lymphoid cells. Perturbations in immune homeostasis precede the inflammation and are detectable in the non-inflamed CD mucosa of patients presenting with anti-GM-CSF autoantibodies. Conclusions: Anti-GM-CSF autoantibodies predict the diagnosis of complicated CD, have unique epitopes, and impair myeloid cell homeostasis across the ILC3-GM-CSF-myeloid cell axis, altering intestinal immune homeostasis long before the diagnosis of disease.