Collagenase production by rheumatoid synovial cells: stimulation by a human lymphocyte factor

Macrophage proteases and rheumatic diseases: regulation of plasminogen activator by thymus-derived lymphocytes

Macrophages in culture secrete a variety of products including neutral protease activities such as plasminogen activator(s) (P.A.), collagenase and elastase. These products are not made by unstimulated macrophages, but only after induction by inflammatory stimuli, phagocytosis and lymphokines. Phagocytosis induces the prompt release of high levels of P.A. by endotoxin-primed macrophages and prolonged secretion follows uptake of non-degradable particles. Stimulation of lymphocytes results in the release of a supernatant product which enhances P.A. secretion by unstimulated mouse macrophages up to 5-fold. The production of the P.A. inducer (P.A.I.) is immunologically specific and is found in allogeneic mixed leukocyte culture (MLC) reactions, but not in syngeneic controls. The P.A. is also induced in activated macrophages from animals infected with BCG of T. cruzi and challenged with specific antigen. Production of the P.A.I. in MLC reactions depends on the presence of thymus-derived (T) lymphocytes and is closely correlated with the appearance of macrophage migration inhibition factor (MIF). The induction of macrophage P.A. and other proteases provides an important pathway for activating macrophages in delayed hypersensitivity reactions and could contribute significantly to tissue destruction in chronic inflammatory diseases in joints.

A new factor that may control collagen resorption

Specific collagenases responsible for the initial enzymic step leading to degradation of the collagen fibrils of connective tissues have been found in both latent and active forms. The most important factor controlling the local activity of collagenase extracellularly may be an inhibitor that is synthesised by connective tissues, and it is proposed that latent enzymes are all enzyme-inhibitor complexes.

Endogenous activation of latent collagenase by rheumatoid synovial cells. Evidence for a role of plasminogen activator

To elucidate the mechanism of synovial damage in rheumatoid arthritis, we studied the activation of latent collagenases released from adherent rheumatoid synovial cells in culture. Latent enzyme was not complexed with alpha2 macroglobulin, the prinicpal proteinase inhibitor in serum, and could be activated by trypsin in the presence of alpha2 macroglobulin if sufficient proteinase was added to saturate inhibitor. Latent collagenase bound half as effectively to collagen fibrils as active enzyme. Plasmin was a threefold better activator of latent enzyme than trypsin and could be generated by addition of plasminogen to synovial-cell cultures. Production of both collagenase and plasminogen activator was inhibited by dexamethasone (10(-9) M). These studies emphasize in importance of control of activation in regulation collagenase activity, It is likely that rheumatoid synovium produces both latent collagenase and plasminogen activator; plasmin is activated from its zymogen, plasminogen, present in inflamed tissues, and in turn activates collagenase.

Prostaglandin production by rheumatoid synovial cells: stimulation by a factor from human mononuclear Cells

Human peripheral blood mononuclear cells (lymphocyte-monocyte) in culture release a solube factor which can stimulate, up to 200-fold, production of prostaglandin E2 by isolated, adherent, rheumatoid synovial cells. Production of the factor by the mononuclear cells is enhanced by phytohemagglutinin. This factor is similar in apparent mol vt (10,000-20,000) to that which also stimulates collagenase production by the same cells.