While a recent experimental postmenopausal osteoporosis study in C57BL/6 SPF vs. GF mice demonstrated the commensal gut microbiota induces the upregulation of marrow TNF, IL17a, and IFNγ in sex steroid deprivation states28, the current study reveals the commensal gut microbiota enhances marrow T-lymphocyte expression of osteoclastogenic cytokines in health. The gene discussed is IL17A; the disease is postmenopausal osteoporosis.