Bone resorption by cells isolated from rheumatoid synovium.

Cellular mechanisms accounting for the osteolysis of rheumatoid erosions are poorly understood. Cells were isolated and characterised from the synovium of 16 patients with rheumatoid arthritis (RA) and four patients with osteoarthritis and their ability to resorb bone was assessed using a scanning electron microscope bone resorption assay. Macrophages were the major cell type isolated from the synovium of patients with RA. These produced extensive roughening of the bone surface without resorption pit formation. This low grade type of bone resorption was not affected by systemic (calcitonin, parathyroid hormone, 1,25-dihydroxyvitamin D3) or local (interleukin 1, prostaglandin E2) factors influencing bone resorption. Macrophage mediated bone resorption differs qualitatively and quantitatively from that of osteoclasts but is likely to play an important part in the development of marginal erosions in RA.