ScRNA-Seq analysis of human CD5+ innate-like B cells identifies AHR expression as a marker of human CD9+ IL-10+ BRegulatory cells

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Abstract B lymphocytes are adaptive immune cells responsible for the production of antigen specific antibodies and the release of pro- and anti-inflammatory cytokines. A previous report from our laboratory found that human, primary CD5+ innate-like B cells (ILB) were preferentially sensitive to aryl hydrocarbon receptor (AHR)-mediated immune suppression compared to CD5− adaptive B cells. CD5+ ILB are a heterogenous population of B cells unified by their expression of CD5 and thought to encompass IgM memory B cells, human B1 B cells, marginal zone B cells, and regulatory B cells among others. Specifically, we demonstrated that CD5+ ILB were marked by elevated expression of programmed cell death protein-1 (PD-1) and its ligands. We also identified a putative role for AHR in the expression of PD-1, suggesting AHR may be important for B cell regulatory functions. Unlike TRegulatory cells, BRegulatory cells are heterogenous, unidentifiable by FoxP3 expression, and express a wide range of surface proteins. To elucidate AHR expression in human B cell populations, naïve, circulating CD19+ B cells were isolated directly from PBMC and enriched for CD5 expression. We then used single cell RNA-sequencing (scRNA-seq) to identify different B cell subsets found within human CD5+ ILB. We found that AHR expression was strongly correlated with expression of CD9 and IL10 as well as CYP1B1. Interestingly, CD9 is reported as a marker of IL-10 producing Bregs suggesting a role for AHR in Breg IL-10 production. These findings were confirmed directly with qRT-PCR and flow cytometry. (Supported by NIH grant P42ES004911) Supported by NIH grant P42ES004911