Interactions among rheumatoid synovial cells and monocyte-macrophages: production of collagenase-stimulating factor by human monocytes exposed to concanavalin A or immunoglobulin Fc fragments.

Adherent synovial cells (ASC) were obtained from minced synovium from patients with rheumatoid arthritis by dissociating the lining cells from the extracellular matrix and dispersing them with proteases. These cells produce high levels of latent collagenase in primary culture. With passage of ASC, collagenase levels decrease but can be stimulated by a soluble factor (MCF) released in vitro from cultured human blood monocyte-macrophages. Monocyte cultures exposed to aggregated immunoglobulin, Fc fragments of immunoglobulin or concanavalin A (Con A) increase production of MCF several-fold more than the control cultures. MCF production by monocytes exposed to Fab fragments does not differ from controls. Although aggregated immunoglobulin, Fc fragments, and Con A stimulate PGE2 synthesis and secretion by human monocytes, the effects on MCF production are not mediated by PGE2 since concentrations of indomethacin that completely block PGE2 production do not inhibit MCF production. These findings of increased production of MCF by monocytes in response to substances that probably exert their effects via surface receptors could be relevant in interpreting the in vivo role of immune complexes in diseases associated with connective tissue destruction.