CD14-Positive Cells Support Osteoblast Viability and Mineralization Without Altering Proinflammatory Cytokine Responsiveness

Bone-resident macrophages are increasingly recognized as regulators of bone metabolism, yet their contribution to primary human osteoblast cultures remains poorly understood. We investigated the functional relevance of CD14-positive cells in primary human osteoblast cultures obtained using two isolation methods. CD14-positive cells were depleted by magnetic-activated cell sorting, and non-depleted and depleted cultures were compared regarding cell viability, matrix mineralization, osteogenic and macrophage-associated marker expression, and responses to IL-1β, IL-6, and TNF-α. CD14 depletion reduced cell viability under growth conditions and significantly impaired matrix mineralization in cultures obtained with both isolation protocols. Depletion markedly decreased CD14 and other monocyte/macrophage-associated markers, while the osteogenic cell population was largely preserved, although marker-specific changes suggested altered osteoblast maturation. Despite reduced basal mineralization, IL-1β and TNF-α significantly enhanced mineralization in both non-depleted and CD14-depleted cultures, whereas IL-6 had no significant effect. These findings indicate that CD14-positive cells support basal osteoblast viability, maturation, and mineralization but are not required for the mineralization-promoting effects of IL-1β and TNF-α. Primary human osteoblast cultures should therefore be considered multicellular systems in which macrophage-like cells contribute substantially to basal osteogenic function.