Abstract
OBJECTIVES:
Immune activation and intestinal microbial dysbiosis could induce diarrhea-predominant irritable bowel syndrome (IBS-D). We examined the roles of ileal immunoglobulin A (IgA) and IgA-coated bacteria in IBS-D pathogenesis.
METHODS:
Peripheral blood, fecal samples, and ileal and cecal biopsies were collected from 32 healthy volunteers and 44 patients with IBS-D. Quantitative reverse transcriptase polymerase chain reaction was used to assess differential gene expression. IgA levels in the blood and fecal samples were quantified by an enzyme-linked immunosorbent assay. IgA+ cells were assessed by immunofluorescence imaging. Flow-cytometry-based IgA+ bacterial cell sorting and 16S rRNA gene sequencing (IgA-SEQ) was used to isolate and identify fecal IgA+ bacteria.
RESULTS:
Fecal IgA, particularly IgA1, was upregulated in patients with IBS-D. IgA class switch and B cell–activating factor-receptor were increased in the terminal ileum of patients. The intestinal microbiota composition was altered in patients compared with that in controls. IgA-SEQ showed that the proportion of fecal IgA-coated bacteria was increased significantly in patients with IBS-D. IgA+ bacteria in patients with IBS-D showed higher abundances of Escherichia–Shigella, Granulicatella, and Haemophilus compared with healthy controls and IgA− bacteria in patients with IBS-D. The Escherichia–Shigella IgA coating index was positively correlated with anxiety and depression. The Escherichia–Shigella relative abundance, luminal IgA activity, and some altered IgA-coated bacteria were positively associated with the clinical manifestations of IBS-D.
DISCUSSION:
Microbial dysbiosis may promote the terminal ileal mucosa to produce higher levels of IgA, increasing the proportion of IgA-coated bacteria by activating IgA class switching, which might regulate local inflammation and clinical manifestations in IBS-D. IgA may mediate the effects of microbial dysbiosis on the pathogenesis of IBS-D.
