IL-12 and Mucosal CD14+ Monocyte-Like Cells Induce IL-8 in Colonic Memory CD4+ T Cells of Patients With Ulcerative Colitis but not Crohn's Disease.

BACKGROUND AND AIMS: CD14+ mononuclear phagocytes [MNPs] and T cells infiltrate colon in ulcerative colitis [UC]. Here we investigated how CD14+ MNPs and the cytokines they produce shape the colonic effector T cell profile. METHODS: Colonic or mesenteric lymph node [mLNs] CD4+ T cells isolated from UC or Crohn's disease [CD] patients were stimulated with cytokines or autologous CD14+ MNPs. Cytokine expression was assessed by intracytoplasmic staining and multiplex ELISA. Unsupervised phenotypic multicolour analysis of colonic CD14+ MNPs was performed using the FlowSOM algorithm. RESULTS: Among CD14+CD64+HLA-DR+SIRPα + MNPs, only the pro-inflammatory cytokine-producing CD163- subpopulation accumulated in inflamed UC colon and promoted mucosal IL-1ß-dependent Th17, Th17/Th1, Th17/Th22 but not Th1 responses. Unsupervised phenotypic analysis of CD14+CD64+ MNPs segregated CD163- monocyte-like cells and CD163+ macrophages. Unexpectedly, IL-12, IL-1ß and CD163-, but not CD163+, cells induced IL-8 expression in colonic CD4+ T cells, which co-expressed IFN-γ and/or IL-17 in UC and not CD. The CD163- monocyte-like cells increased the frequency of IL-8+IL-17+/-IFN-γ +/- T cells through IL-1ß and IL-12. Finally, colonic IL-8+ T cells co-expressing GM-CSF, TNF-α and IL-6 were detected ex vivo and, promoted by IL-12 in the mucosa and mLNs in UC only. CONCLUSIONS: Our findings established a link between monocyte-like CD163- MNPs, IL-12, IL-1ß and the detection of colonic memory IL-8-producing CD4+ T cells, which might all contribute to the pathogenesis of UC.

Correction: Two distinct colonic CD14+ subsets characterized by single-cell RNA profiling in Crohn's disease.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Two distinct colonic CD14+ subsets characterized by single-cell RNA profiling in Crohn's disease.

Inflammatory bowel diseases are associated with dysregulated immune responses in the intestinal tissue. Four molecularly identified macrophage subsets control immune homeostasis in healthy gut. However, the specific roles and transcriptomic profiles of the phenotypically heterogeneous CD14+ macrophage-like population in inflamed gut remain to be investigated in Crohn's disease (CD). Here we identified two phenotypically, morphologically and functionally distinct colonic HLADR+SIRPα+CD14+ subpopulations that were further characterized using single-cell RNA-sequencing (scRNAseq) in CD. Frequencies of CD64hiCD163-/dim cells selectively augmented in inflamed colon and correlated with endoscopic score of disease severity. IL-1ß and IL-23-producing CD64hiCD163-/dim cells predominated over TNF-α-producing CD64hiCD163hi cells in lesions. Purified "inflammatory monocyte-like" CD163-, but not "macrophage-like" CD163hi cells, through IL-1ß, promoted Th17/Th1 but not Th1 responses in tissue memory CD4+T cells. Unsupervised scRNAseq analysis that captures the entire HLADR+SIRPα+ population revealed six clusters, two of which were enriched in either CD163- or CD163hi cells, and best defined by TREM1/FCAR/FCN1/IL1RN or CD209/MERTK/MRCI/CD163L1 genes, respectively. Selected newly identified discriminating markers were used beyond CD163 to isolate cells that shared pro-Th17/Th1 function with CD163- cells. In conclusion, a molecularly distinct pro-inflammatory CD14+ subpopulation accumulates in inflamed colon, drives intestinal inflammatory T-cell responses, and thus, might contribute to CD disease severity.