CD163L1⁺CXCL10⁺ Macrophages are Enriched Within Colonic Lamina Propria of Diverticulitis Patients

Background: Inflammation of diverticula, which are outpouchings of the colonic bowl wall, causes diverticulitis. Severe cases of diverticulitis require surgical intervention. Through RNA-seq analysis of intestinal tissues, we previously found that the innate immune response was deregulated in surgical diverticulitis patients. In that study, pro-inflammatory and macrophage markers were differentially expressed in the colons of diverticulitis versus control patients. Here we investigate CD163L1⁺ macrophages and the pro-inflammatory chemokine, CXCL10, in diverticulitis. Materials and Methods: We assessed tissue from an uninvolved area adjacent to a region of the sigmoid colon chronically affected by diverticulitis and performed Spearman's correlation on transcripts associated with macrophage signaling. We identified altered CD163L1 and CXCL10 gene expression levels that we confirmed by RT-qPCR analysis on an independent cohort of diverticulitis patients and controls. We used immunofluorescence microscopy to localize CD163L1⁺ macrophages and CXCL10 levels in intestinal tissue and ELISA to measure CXCL10 levels in patient serum. Results: We found a positive correlation between intestinal CD163L1 and CXCL10 gene expression and an increased number of CD163L1⁺ macrophages in the sigmoid colons of diverticulitis patients relative to controls (P = 0.036). Macrophages at the apices of colonic crypts expressed the chemokine CXCL10. Correspondingly, these diverticulitis patients also displayed heightened CXCL10 levels in their serum (P = 0.007). Conclusions: We identified a novel population of CD163L1⁺CXCL10⁺ macrophages in the colonic crypts of diverticulitis patients and demonstrated increased expression of serum CXCL10 in these patients. CXCL10 may serve as a prognostic biomarker to aid in clinical decision making for diverticulitis patients.