Setaria cervi collagenase: IgG cleavage and inhibition by Wuchereria bancrofti infected sera

Significant protease activity has been detected in somatic extract of adults and microfilarial stage of Setaria cervi, using general protease substrates and collagen. The pH optima studies of the somatic extract of adult females showed two peaks at 7.0 and 5.0 for collagenase activity. Both forms were purified using sequential DEAE-sepharose and Sephadex G-100 column chromatography. The purified enzymes had the molecular masses of 175 and 20 kDa and pH optima at 7.0 and 5.0, respectively. The 175 kDa collagenase was more sensitive to metal chelators and serine protease inhibitors. However, 20 kDa collagenase was sensitive to cysteine protease inhibitors. The IgG antibodies from W. bancrofti infected human sera inhibited both enzymes. Further the purified collagenases were used to digest total human IgG at their respective pH and for different lengths of time. The 175 kDa protein was capable of cleaving human IgG. The digestion appeared to be restricted to a single cleavage point of H-chain within the hinge region of IgG molecule and produced fragments of similar molecular mass (27 kDa) indicating cleavage to Fab and Fc fragments. The degree of digestion was found to be proportional to the incubation time at 37°C. No further digestion of either fragments were observed. The L-chains were apparently resistant to collagenase digestion in all cases. Thus, the results suggest that S. cervi collagenase might be involved in the defense mechanisms of the parasite against the immune response of the host.