Mast cells help organize the Peyer’s patch niche for induction of IgA responses

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Peyer’s patches (PPs) support the production of intestinal IgA. Induction of IgA+ cells in PPs requires interactions between B cells and conventional dendritic cells type 2 (cDC2s) in the subepithelial dome (SED). We found that cDC2s express GPR35, a receptor that promotes migration to 5-hydroxyindoleacetic acid (5-HIAA). In mice lacking GPR35, there was a loss of cDC2s from the SED and of IgA+ cells. Mast cells were present in the SED and ablation of 5-HIAA production in mast cells phenocopied the absence of GPR35. Thus, mast cell-guided positioning of GPR35+ cDC2s in the SED supports induction of intestinal IgA responses.