Activation of the alternative complement pathway by 405 nm light in serum from porphyric rat

Sera from hexachlorobenzene-induced porphyric rats were examined for evidence of complement activation. The serum irradiated in vitro with 405 nm light resulted in a dose-dependent diminution of the total hemolytic activity of the complement. Further, such irradiated serum showed immunoelectrophoretical C3 conversion and chemotactic activity for rat polymorphonuclear leukocytes, and caused increased vascular permeability in vivo. C3 conversion was not induced in serum chelated with EDTA, but occurred in serum chelated with Mg++-EGTA. By sephadex G-75 chromatography, the irradiated serum had potent chemotactic activity eluted near the cytochrome C marker. These studies indicate that the irradiation of porphyric rat serum with 405 nm light induces activation of the complement system via the alternative pathway, with the resultant development of anaphylatoxin.