NEUTROPHIL CHEMOTACTIC ACTIVITY AND C5A FOLLOWING SYSTEMIC ACTIVATIONOF COMPLEMENT IN RATS

Using ELISA analysis, rat C5a was stimulated in serum from rats underg oing systemic activation of complement after intravenous infusion of p urified cobra venom factor (CVF). Biological (neutrophil chemotactic) activity was also assessed. Serum levels of C5a were directly proporti onal to the amount of CVF infused. C5a and neutrophil chemotactic acti vity, peaked by 5 min, then plateaued. In vitro addition of anti-C5a t o serum samples of CVF-infused rats totally abolished chemotactic acti vity, indicating that all biological activity could be ascribed to C5a . Blood neutrophils obtained from CVF-iniused animals showed a signifi cant upregulation of CD11b, the increase being reduced (38%) in animal s pretreated with anti-C5a. These findings indicate that infusion of C VF into rats produces generation of C5a, all chemotactic activity in s erum being related to C5a. The in vivo generation of C5a is, at least inpart, responsible for upregulation of CD11b on blood neutrophils.