In vitro and in vivo responses of murine granulocytes to human complement-derived, haemolytically inactive C5b67 (iC5b67)

Haemolytically inactive C5b67 (iC5b67), which was made from purified human components and decayed to a haemolytically inactive form, was evaluated as an agonist for murine leucocytes both in vitro and in vivo. In an in vitro assay, iC5b67 stimulated chemotaxis for both neutrophils purified from mous e bone marrow and splenic eosinophils of IL-5 transgenic mice. The stimulat ion was dose-dependent, with high dose inhibition. As with human neutrophil s, iC5b67 also failed to up-regulate CR3 (CD 11b/CD18) expression and to st imulate superoxide generation in murine bone marrow neutrophils, in vitro. In vivo, iC5b67 elicited an inflammatory response in a mouse model of pleur itis. A marked infiltration of neutrophils, which peaked at 4 h, was follow ed by an infiltration of eosinophils and mononuclear leucocytes. This infla mmatory response was dose- and time-dependent. However, the protein concent ration in the pleural wash fluid did not increase, indicating that iC5b67 d id not induce a capillary leak. Although the infiltration of neutrophils co uld not be reproduced by pure C7 or human serum albumin (HSA), C5b6 did ind uce an influx of neutrophils. We were able to document the existence of C7, both antigenically and functionally, in pleural washes of normal mice, mak ing it likely that the activity of C5b6 resulted from the in situ formation of C5b67 and iC5b67. The mouse model of pleuritis promises to be a useful in vivo system in which to evaluate the pro- and anti-inflammatory effects of iC5b67 that have been noted in vitro.