MUCOSAL IMMUNE SIGNATURES OF PERIANAL FISTULIZING CROHN’S DISEASE BY MASS CYTOMETRY

Abstract

Abstract BACKGROUNDS Perianal fistulas occur in ~30-40% of patients associated with high morbidity and an impaired quality of life. The management of perianal fistulizing CD is a major clinical challenge, where its underlying etiology of is poorly understood. METHODS We recruited patients with a history of: 1) CD with perianal fistulas; 2) CD without perianal involvement; 3) idiopathic perianal fistulas. Biopsies were taken from the fistula tracts, external opening of the fistulas, and rectal mucosa during examination under anesthesia or colonoscopy. Isolated mucosal immune cells were analyzed using mass cytometry. Data was analyzed using viSNE for dimensionality reduction. RESULTS We have revealed previously unknown mucosal immune landscapes in perianal CD using mass cytometry. Key cell populations with significant difference in frequencies are summarize in Table 1 (data of external fistula opening not shown due to limited space): 1) CD45RO+ T cells including Tregs are elevated in CD fistulas compared to those from idiopathic fistulas, which is consistent with a prior histological study. The expression of co-inhibitory receptor TIGIT and co-stimulatory receptor CD226 are increased in Tregs in CD fistulas, although their function in IBD and especially perianal CD remains unclear. 2) Perianal CD is associated with increased Th17 cells in the fistula tracts and elevated IL-17-producing CD8 T cells (Tc17) in the rectum, which highlight the importance of IL-17 signaling in perianal CD. 3) CD fistulas show increased CD39 and decreased CD127 (IL-7Ra) in both CD4 and CD8 T cells. CD39 and CD127 are markers of T cell exhaustion, which may control the pathogenesis of perianal CD by regulating cytokine production. 4) Total B cells are elevated in CD fistulas compared to idiopathic fistulas. In contrast, regulatory B cells (Bregs), with immunomodulatory function in the gut, are dramatically diminished in CD fistulas compared to idiopathic fistulas. 5) Besides adaptive cells, CD3-CD19- innate immune cells including innate lymphoid cells (ILCs), macrophages, and NK cells are also skewed in perianal CD. Fistula tracts, external fistula opening (data not shown), and rectum of perianal CD all show dramatically elevated CD172+TREM1+ macrophages, which were previously found to promote chronic inflammation in luminal CD. CONCLUSIONS The immune responses in perianal CD demonstrate unique features that are not present in luminal CD (summarized in Figure 1). This indicates that perianal CD represents an immune identity distinct from luminal CD in the intestine. Importantly, altered T cell exhaustion markers (CD39 and CD127) and increased CD172+TREM1+ pathogenic macrophages are present in all three locations (fistula tracts, external opening, and rectum) of perianal CD, suggesting their roles in the pathogenesis of perianal CD and may become novel therapeutic targets.