Arianna Calcinotto et al. reported that in the mouse model Vk * MYC, Prevotella hepatica promoted the differentiation of Th17 cells in the intestine and migrated to the bone marrow to secrete IL-17, thus promoting MM progression, suggesting that commensal bacteria release a paracrine signaling network between innate and adaptive immunity to accelerate MM progression. Here, IL17A is linked to Miyoshi myopathy.