[Inhibition of Cls activity by methylprednisolone]

From a clinical study it was found that serum ClINH activity increased 6 hours after methylprednisolone (MP) pulse therapy in all the patients we studied with connective tissue diseases. Furthermore plasma ClINH-Cls complex decreased after pulse therapy. These phenomena lead us to investigate the effect of MP on Cls. 1) When a constant amount of Cls (8 micrograms/ml) was incubated with several concentrations of MP (2-50 mg/ml), the Cls activity of consuming C4 hemolysis was inhibited by MP in a dose-dependent manner. 2) MP inhibited consumption of C2 as well as C4 by Cls in a dose-dependent manner, even when MP had been removed by dialysis following incubation with Cls. These experimental data suggested that the trace amounts of Cls generated by immune complexes could be inhibited by long circulation of MP even at low concentrations in vivo, and resulted in a decrease of ClINH consumption and ClINH-Cls complex formation. These results indicated that the inhibition of Cls activity is one of the most important mechanisms in the process of the anti-inflammatory effect of MP in vivo.