Secretory IgA binding to FCRL3 triggers shared inflammatory cytokine secretion by human regulatory T cells and effector T cells

Several human lymphocyte subsets express the novel secretory IgA receptor FCRL3. Secretory IgA binding to FCRL3 mAb diminishes the inhibitory capacity of regulatory T cells and promotes a Th17-like phenotype. Here we report that in CD4+ regulatory T cells and CD8+ terminal effector T cells secretory IgA induced a shared inflammatory gene signature that included PTGS2 encoding COX2, and the prototypic inflammatory cytokine genes IL1A, IL1B, and IL8. Secretory IgA in regulatory T cells also elevated gene transcripts required for lineage identity and function. Secretory IgA promoted IL-1β, IL-6, IL-8, IL-10, IFN-γ, and TNF-α protein secretion by both T cell types. . We propose that secretory IgA provokes in regulatory and effector T cells a coordinated inflammatory response to facilitate mucosal pathogen clearance.