Circulating and Tissue-Resident CD4+ T Cells With Reactivity to Intestinal Microbiota Are Abundant in Healthy Individuals and Function Is Altered During Inflammation

Abstract

Background & AimsInteractions between commensal microbes and the immune system are tightly regulated and maintain intestinal homeostasis, but little is known about these interactions in humans. We investigated responses of human CD4+ T cells to the intestinal microbiota. We measured the abundance of T cells in circulation and intestinal tissues that respond to intestinal microbes and determined their clonal diversity. We also assessed their functional phenotypes and effects on intestinal resident cell populations, and studied alterations in microbe-reactive T cells in patients with chronic intestinal inflammation.MethodsWe collected samples of peripheral blood mononuclear cells and intestinal tissues from healthy individuals (controls, n = 13−30) and patients with inflammatory bowel diseases (n = 119; 59 with ulcerative colitis and 60 with Crohn’s disease). We used 2 independent assays (CD154 detection and carboxy-fluorescein succinimidyl ester dilution assays) and 9 intestinal bacterial species (Escherichia coli, Lactobacillus acidophilus, Bifidobacterium animalis subsp lactis, Faecalibacterium prausnitzii, Bacteroides vulgatus, Roseburia intestinalis, Ruminococcus obeum, Salmonella typhimurium, and Clostridium difficile) to quantify, expand, and characterize microbe-reactive CD4+ T cells. We sequenced T-cell receptor Vβ genes in expanded microbe-reactive T-cell lines to determine their clonal diversity. We examined the effects of microbe-reactive CD4+ T cells on intestinal stromal and epithelial cell lines. Cytokines, chemokines, and gene expression patterns were measured by flow cytometry and quantitative polymerase chain reaction.ResultsCirculating and gut-resident CD4+ T cells from controls responded to bacteria at frequencies of 40−4000 per million for each bacterial species tested. Microbiota-reactive CD4+ T cells were mainly of a memory phenotype, present in peripheral blood mononuclear cells and intestinal tissue, and had a diverse T-cell receptor Vβ repertoire. These cells were functionally heterogeneous, produced barrier-protective cytokines, and stimulated intestinal stromal and epithelial cells via interleukin 17A, interferon gamma, and tumor necrosis factor. In patients with inflammatory bowel diseases, microbiota-reactive CD4+ T cells were reduced in the blood compared with intestine; T-cell responses that we detected had an increased frequency of interleukin 17A production compared with responses of T cells from blood or intestinal tissues of controls.ConclusionsIn an analysis of peripheral blood mononuclear cells and intestinal tissues from patients with inflammatory bowel diseases vs controls, we found that reactivity to intestinal bacteria is a normal property of the human CD4+ T-cell repertoire, and does not necessarily indicate disrupted interactions between immune cells and the commensal microbiota. T-cell responses to commensals might support intestinal homeostasis, by producing barrier-protective cytokines and providing a large pool of T cells that react to pathogens.

The microbiome and immune memory formation

“…Some studies have investigated how the intestinal microbiota, in the absence of pathogens, affects formation of memory T‐cell populations. The Powrie group has demonstrated that circulating and intestinal tissue‐resident memory CD4 T cells with a diverse T‐cell receptor repertoire and reactivity to the intestinal microbiota are present in healthy individuals . These microbiota‐reactive memory T cells in healthy individuals promoted intestinal stromal and epithelial cell activation through the secretion of interleukin (IL)‐17A, interferon gamma and tumor necrosis factor.…”

“…These microbiota‐reactive memory T cells in healthy individuals promoted intestinal stromal and epithelial cell activation through the secretion of interleukin (IL)‐17A, interferon gamma and tumor necrosis factor. Furthermore, the function of these microbiota‐specific memory T cells was altered during inflammation resulting in reduced numbers in blood compared with intestine and increased frequency of IL‐17A production when compared to healthy individuals …”

“…The Powrie group has demonstrated that circulating and intestinal tissue-resident memory CD4 T cells with a diverse T-cell receptor repertoire and reactivity to the intestinal microbiota are present in healthy individuals. 39 These microbiota-reactive memory T cells in healthy individuals promoted intestinal stromal and epithelial cell activation through the secretion of interleukin (IL)-17A, interferon gamma and tumor necrosis factor. Furthermore, the function of these microbiota-specific memory T cells was altered during inflammation resulting in reduced numbers in blood compared with intestine and increased frequency of IL-17A production when compared to healthy individuals.…”

“…Furthermore, the function of these microbiota-specific memory T cells was altered during inflammation resulting in reduced numbers in blood compared with intestine and increased frequency of IL-17A production when compared to healthy individuals. 39 Another, more recent, mouse study demonstrated that Treg and memory T cells establish long-term residence in secondary lymphoid organs. 40 Interestingly, only residency in Peyer's patches was affected by the intestinal microbiota.…”

Transplant associated infections—The role of the gastrointestinal microbiota and potential therapeutic options

“…The intestinal microbiota plays an important role in regulating the immune system . Signals such as T regulatory cell (T regs) and T helper 17 (Th17) cells have been shown to prime immune responses and regulate both pro‐ and anti‐inflammatory host immune responses .…”