The immunosuppression mechanism of hypodermin A on complement

Hypodermin A (HA), a serine protease secreted by first-instar larvae of Hypoderma lineatum (Diptera: Oestridae) is associated with inflammatory and the specific immune responses in cattle hosts. In the present study, the cDNA sequence of HA was synthesized, and found to have fifteen amino acids which differed from the sequence available in GenBank. We then examined the association between recombinant HA and guinea-pig complement component 3 (C3) through a co-immunoprecipitation assay. Cos7 cells stably expressing HA were generated, and were found to be more resistant to lysis by guinea-pig C3 than the controls. HA was also able to degrade the C6 and C5b-9 of guinea-pig C3. The presumed DNA binding site of HA with guinea-pig C3 was detected by an electrophoretic mobility shift assay (EMSA). In contrast, after stable transfection, mHA was unable to reduce the amount of C3 or to inhibit its cytotoxicity, while HA could degrade guinea-pig C3 and inhibit the complement pathway. The findings suggest that recombinant HA could serve as an immunosuppressive agent against organ rejection after xenotransplantation.