Chemotactic activity generated in human serum from the fifth component of complement by hydrogen peroxide

Exposure of normal human serum to various concentrations of hydrogen peroxide as low as 68.8 microM resulted in the generation of chemotactic activity for human neutrophils, which was inhibited by adding catalase prior to the exposure. Maximum chemotactic activity was obtained by hydrogen peroxide at a concentration of 1.1 mM, and the concentration greater than 1.1 mM expressed decreased activity. On the contrary, hydrogen peroxide less than 1.1 mM produced dose-dependent chemotactic activity. The generation of chemotactic activity is initiated at an incubation time of 5 minutes, and subsequently increases with up to 90 minutes. The suppression of chemotactic activity was minimum even after 180 minutes. The maximum activity was obtained by 1024-fold dilution of serum treated with 13.8 mM hydrogen peroxide. These results suggest that the disappearance of chemotactic activity at the high-dose range of hydrogen peroxide is due to neutrophil deactivation rather than inactivation of the chemotactic activity after it was generated. Similarly, purified human C5 exposed to hydrogen peroxide generated chemotactic activity. The chemotactic activity was inhibitable by antiserum to human C5. The molecular weight of chemotactically active substance was approximately 15,000. The generation of chemotactic activity was not inhibited by addition of EGTA or EDTA. These results imply that hydrogen peroxide generates C5a-like chemotactic factor through hydrolysis of C5.