Abstract
The intestinal mucosa in inflammatory bowel disease (IBD) contains increased frequencies of lymphocytes and a disproportionate increase in plasma cells secreting immunoglobulin (Ig)G relative to other isotypes compared to healthy controls. Despite consistent evidence of B lineage cells in the mucosa in IBD, little is known of B cell recruitment to the gut in IBD. Here we analyzed B cells in blood of patients with Crohn's disease (CD) and ulcerative colitis (UC) with a range of disease activities. We analyzed the frequencies of known B cell subsets in blood and observed a consistent reduction in the proportion of CD27−IgD− B cells expressing all Ig isotypes in the blood in IBD (independent of severity of disease and treatment) compared to healthy controls. Successful treatment of patients with biologic therapies did not change the profile of B cell subsets in blood. By mass cytometry we demonstrated that CD27−IgD− B cells were proportionately enriched in the gut-associated lymphoid tissue (GALT) in IBD. Since production of TNFα is a feature of IBD relevant to therapies, we sought to determine whether B cells in GALT or the CD27−IgD− subset in particular could contribute to pathology by secretion of TNFα or IL-10. We found that donor matched GALT and blood B cells are capable of producing TNFα as well as IL-10, but we saw no evidence that CD27−IgD− B cells from blood expressed more TNFα compared to other subsets. The reduced proportion of CD27−IgD− B cells in blood and the increased proportion in the gut implies that CD27−IgD− B cells are recruited from the blood to the gut in IBD. CD27−IgD− B cells have been implicated in immune responses to intestinal bacteria and recruitment to GALT, and may contribute to the intestinal inflammatory milieu in IBD.
Highlights
Inflammatory bowel disease (IBD) encompasses two clinical entities: Crohn’s disease (CD) and ulcerative colitis (UC)
In order to assess relative frequencies of the main B cell subsets in peripheral blood of CD and UC patients, we subjected the peripheral blood mononuclear cells (PBMCs) of patients with various disease activities and treatments to six color flow cytometry
Depletion of CD27−IgD− B cells from the blood is seen in patients with both CD and UC even when patients are in remission and when disease activity is low
Summary
Inflammatory bowel disease (IBD) encompasses two clinical entities: Crohn’s disease (CD) and ulcerative colitis (UC). While the exact etiology of both diseases is still not clearly understood, current literature suggests that an aberrant immune response to the intestinal flora contributes to pathology in genetically susceptible individuals [1,2,3]. The evidence for this is stronger for CD than for UC [4], which can be associated with autoimmune conditions like primary sclerosing cholangitis (PSC) in a small subgroup of patients [5]. Whilst big strides have been made in developing biologic therapies for both diseases, a significant proportion of patients with CD and UC remain treatment refractory, highlighting the unmet need for a better understanding of the mechanisms contributing to the pathogenesis of both diseases [8, 9]
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