Modulation of neutrophil expression of C3b receptors (CR1) by soluble monomeric human C3b.
Upon incubation at 37 degrees C with purified human C3b (500 micrograms/ml), polymorphonuclear neutrophils (PMN) were found to express up to 50% more C3b receptors (CR1) than PMN incubated with buffer alone. This up-regulation of CR1, assessed by the binding of radiolabeled CR1-specific monoclonal antibody, was dependent on the dose of C3b, occurred within 10-20 min and was stable for at least 90 min. PMN incubated with C3b also demonstrated enhanced CR1-dependent binding functions, such as EC3b rosette formation and phagocytosis of EIgGC3b particles. C3b at a concentration of 500 micrograms/ml induced up to 90% increase in the attachment or the phagocytic index. However, CR1 remained unable to promote phagocytosis of EC3b intermediates. Fc receptor-mediated functions were unaffected by the treatment with C3b. The active factor was characterized as monomeric C3b and, in particular, shown to be distinct from C5a. C3b purified by anion-exchange fast protein liquid chromatography on a Mono Q column or eluted from a monoclonal anti-C3b-Sepharose retained its modulating activity, while native C3 or C3 fragments such as iC3b, C3c or C3d,g were ineffective.
D000911:Antibodies, Monoclonal; D002462:Cell Membrane / Q000378:metabolism; D003176:Complement C3 / Q000378:metabolism*; D003179:Complement C3b / Q000378:metabolism*; D003182:Complement C5 / Q000378:metabolism; D015936:Complement C5a; D006801:Humans; D009504:Neutrophils / Q000378:metabolism* / Q000502:physiology; D011951:Receptors, Complement / Q000378:metabolism*; D017463:Receptors, Complement 3b; D012397:Rosette Formation; D012995:Solubility
D000911:Antibodies, Monoclonal; D003176:Complement C3; D003182:Complement C5; D011951:Receptors, Complement; D017463:Receptors, Complement 3b; D003179:Complement C3b; D015936:Complement C5a