Membrane-associated interleukin-1 promotes osteoclast-like cell formation in vitro

The effect of paraformaldehyde-fixed murine macrophage P388D₁ cells on osteoclast-like cell formation was investigated in mouse marrow cultures. When mouse marrow cells were cocultured for 8 days with paraformaldehyde-fixed P388D₁ cells stimulated with lipopoly-saccaride (LPS), many tartrate-resistant acid phosphatase (TRACP)-positive multinucleated cells were formed. Non-stimulated, and paraformaldehyde-fixed P388D₁ cells did not induce the formation of TRACP-positive multinucleated cells. Salmon calcitonin and indomethacin strongly inhibited the paraformaldehyde-fixed, LPS-stimulated P388D₁ cells-induced TRACP-positive multinucleated cell formation. Monospecific anti-mouse recombinant IL-lα serum inhibited TRACP-positive multinucleated cell formation in the presence of paraformaldehyde-fixed P388D₁ cells stimulated with LPS. These results suggest that membrane-associated IL-1 on macrophages is responsible for the resorptive effect of paraformaldehyde-fixed P388D₁ cells stimulated with LPS.