Differential Patterns of C3b Receptor Expression on Guinea Pig Macrophages

Initial investigations revealed that the expression of C3b receptors on macrophages was markedly influenced by the manner in which the cells were obtained. Resident (wash-out), glycogen-induced and oil-induced guinea pig peritoneal cells were harvested and adherent cell monolayers were cultured in a serum-free Dulbecco's medium at equivalent cell concentrations. Monolayers contained 90 to 95% macrophages as assessed by nonspecific esterase activity and latex ingestion. Macrophage membrane C3b receptors were detected by rosetting with EIgMC143b^gp indicator cells (100 IgM sites/indicator cell; 20 RBC/macrophage) at varying times after initiation of culture. Marked differences in C3b receptor expression were observed among the three macrophage populations. 81%±4% of resident peritoneal macrophages rosetted with EIGMC143b^gp indicator cells at the initiation of culture and minimal decline in C3b receptor expression occurred at 16 hr of culture (70%±5% rosettes). In contrast, 35%±8% of oil-induced peritoneal macrophages rosetted initially and by 16 hr only 15%±9% of these cells formed rosettes with C3b-bearing indicator cells.