ICAM-1-mediated osteoblast-T lymphocyte direct interaction increases mineralization through TGF-β1 suppression

Modulation of osteoblast functions by T lymphocytes is important in inflammation-associated mineralized tissue diseases. The study aimed to determine whether direct interaction between these two cell types affects osteoblast functions and mineralization. The results showed that direct contact between the two cell types was evident by scanning electron microscopy and transmission electron microscopy. Under osteogenic induction, higher hydroxyapatite precipitation was observed in cocultures with direct contact with T lymphocytes compared with that by osteoblasts cultured alone. Cocultures without direct cell contact caused a decrease in mineralization. Direct cell contact also upregulated intercellular adhesion molecule (ICAM)-1 and simultaneously downregulated transforming growth factor (TGF)-β1 in osteoblasts. However, the downregulation of TGF-β1 was reversed by ICAM-1 blocking. Exogenously added TGF-β1 in cocultures with direct cell contact suppressed mineralization. In conclusion, studies are consistent with ICAM-1-mediated direct contact between osteoblasts and T lymphocytes increasing mineralization via downregulation of TGF-β1 in osteoblasts in vitro. This suggests a possible unexpected, but crucial, role of T lymphocytes in enhancing matrix mineralization during the repair process in vivo. The study identifies ICAM-1/TGF-β1 as possible novel therapeutic targets for the treatment and prevention of inflammation-associated mineralized tissue diseases.