We investigated, in five cell strains per experiment, whether several cytokines known or believed to have effects on bone resorption were produced by nearly homogeneous strains of cultured normal human osteoblast-like (hOB) cells that display virtually the complete phenotype of the mature osteoblast. In unstimulated hOB cells, we detected constitutive production of interleukin-6 (IL-6) (mean + se, 122 ± 32 pg/ml) and IL-8 (135 ± 39 pg/ml), but not of IL-4, granulocyte-macrophage colony-stimulating factor (GM-CSF), or tumor necrosis factor-α (TNFα). IL-1β in doses from 1-100 U/ml stimulated dose-dependent increases in IL-6 (r = 0.87; P < 0.001) and IL-8 (r = 0.95; P < 0.001). Similar increases occurred after stimulation with TNFα in doses from 3-300 U/ml. IL-1β and TNFα also stimulated GM-CSF production, but only at higher doses. 17β-Estradiol (10-8M) had no significant effect on the secretion of any of these cytokines, either constitutively or after stimulation with IL-1β or TNFα. Stimulated production of IL-4 was not detected after treatment with IL-1β or TNFα, and that of TNFα was not detected after treatment with IL-1β. We conclude that IL-6, IL-8, and GM-CSF, but not IL-4 and TNFα, are produced by highly differentiated normal human cells of the osteoblast lineage, but their secretion is not regulated by estrogen. However, we cannot exclude the possibility that estrogen regulation of these cytokines may occur during early stages of osteoblast differentiation.
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