Determination of C3b receptors on normal and patient polymorphonuclear neutrophils with C3b-coated fluorescent...

A method, devised in the authors' laboratories, for the determination of C3b receptors on normal and patient neutrophils using C3b-coated fluorescent microspheres, was applied to the quantitation of C3b receptors on the neutrophils of several patients suffering from burns and trauma and a patient with pancreatitis. From three to 11 days in the clinical course the relative number of C3b receptors was, or rose to, two to ten times the number of receptors present at later times in the clinical course and, in most of the cases studied, the increase in C3b receptor number coincided with enhanced neutrophil bactericidal function. The rise in C3b receptor number was ascribed to up-regulation by C3a and C5a des Arg from complement activation and also, in the cases where sepsis occurred, to the presence of bacterial chemotactic peptides. Preliminary experiments with zymosan-activated serum and the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine confirmed this explanation.