Commensal bacterial–derived signals regulate basophil hematopoiesis and allergic inflammation

Commensal bacteria that colonize mammalian barrier surfaces are reported to influence T helper type 2 (T(H)2) cytokine–dependent inflammation and susceptibility to allergic disease, although the mechanisms that underlie these observations are poorly understood. In this report, we identify that deliberate alteration of commensal bacterial populations via oral antibiotic treatment resulted in elevated serum immunoglobulin E (IgE) levels, increased steady–state circulating basophil populations, and exaggerated basophil–mediated T(H)2 cell responses and allergic inflammation. Elevated serum IgE levels correlated with increased circulating basophil populations in mice and subjects with hyperimmunoglobulinemia E syndrome. Furthermore, B cell–intrinsic expression of MyD88 was required to limit serum IgE levels and circulating basophil populations in mice. Commensal–derived signals were found to influence basophil development by limiting proliferation of bone marrow–resident precursor populations. Collectively, these results identify a previously unrecognized pathway through which commensal–derived signals influence basophil hematopoiesis and susceptibility to T(H)2 cytokine–dependent inflammation and allergic disease.