Migration inhibition factor-like activity in inflammatory synovial fluids might be due to proteases.

Using an assay of macrophage migration, where the cells emigrate from an agarose droplet, it was found that the neutral proteases trypsin, chymotrypsin, Pronase and elastase have MIF-like activity. Appropriate enzyme inhibitors counteract this effect. To twelve synovial fluids from patients with inflammatory arthritis, which have MIF-like activity (migration index between 0-3 and 0-7) protease indhibitors (Trasylol, ovomucoid and soybean inhibitor) were added. Ten of the fluids lost some of their MIF-like activity with at least one inhibitor. Phenylmethylsulphonylfluoride counteracted totally the MIF-like activity of the two fluids tested. It is concluded that MIF-like activity of inflammatory synovial fluids is due, at least partially, to proteases.