Stromal-like Cells Are Found in Peripheral Blood of Inflammatory Bowel Disease Patients and Correlate with Immune Activation State.

INTRODUCTION: Recent studies have identified a critical role for stromal-immune cell interactions in immunity and immune tolerance. Transcriptomic profiling has implicated stromal cells in immune-mediated disorders including the two common forms of inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC). Stromal-immune interactions may edify inflammatory state and the development of IBD-related complications such as fibrosis; yet the lack of protein markers has hampered studying stromal-immune perturbation. METHODS: In this study, we designed a 40-color spectral flow cytometry assay to characterize hematopoietic and nonhematopoietic cells in intestinal biopsies and matched blood samples from patients with CD or UC. RESULTS: We identified circulating stromal-like cells that are significantly more abundant in IBD blood samples than in healthy controls. Those cells expressed podoplanin (PDPN), a commonly used marker for fibroblasts, and they were associated with activated and memory T and B cells, and altered NK cell, monocyte, and macrophage populations. PDPN+ cells in the blood correlated with PDPN+ cells in the colon. Principal component analysis distinctly separated healthy blood samples from IBD blood samples, with stromal-like cells and B cell subtypes dominating the IBD signature; Pearson correlation detected an association between PDPN+ stromal-like cells and B cell populations in IBD blood and gut biopsies. DISCUSSION: These observations suggest that PDPN+ cells in the blood may serve as a biomarker of IBD. Understanding the relationship between stromal cells and immune cells in the intestine and the blood may provide a window into disease pathogenesis and insight into therapeutic targets for IBD.

Lymph Node Stromal Cell-Intrinsic MHC Class II Expression Promotes MHC Class I-Restricted CD8 T Cell Lineage Conversion to Regulatory CD4 T Cells.

MHC class I (MHC-I)-restricted CD4+ T cells have long been discovered in the natural repertoire of healthy humans as well as patients with autoimmune diseases or cancer, but the exact origin of these cells remains to be fully characterized. In mouse models, mature peripheral CD8+ T cells have the potential to convert to CD4+ T cells in the mesenteric lymph nodes. This conversion can produce a unique population of MHC-I-restricted CD4+ T cells including Foxp3+ regulatory T cells termed MHC-I-restricted CD4+Foxp3+ T (CI-Treg) cells. In this study we examined the cellular and molecular elements that promote CD8-to-CD4 lineage conversion and the development of CI-Treg cells in mice. Using adoptive transfer and bone marrow chimera experiments, we found that the differentiation of CI-Treg cells was driven by lymph node stromal cell (LNSC)-intrinsic MHC-II expression as opposed to transcytosis of MHC-II from bone marrow-derived APCs. The lineage conversion was accompanied by Runx3 versus ThPOK transcriptional switch. This finding of a new role for LNSCs in vivo led us to develop an efficient tissue culture method using LNSCs to generate and expand CI-Treg cells in vitro. CI-Treg cells expanded in vitro with LNSCs effectively suppressed inflammatory tissue damage caused by pathogenic CD4+ T cells in mouse models of colitis. This study identified a novel role of MHC-II expressed by LNSCs in immune regulation and the potential utilization of LNSCs to generate novel subsets of immune regulatory cells for therapeutic applications.