Detection of shedding of human blood monocyte fc receptor during in vitro culture

Human monocytes, isolated from peripheral blood and placed in culture, produce supernatants that have Fc receptor activity. This activity is detectable using a complement-dependent h emolytic assay. Inhibition of hemolysis is detected with undiluted supernatants, is temperature-dependent and is not demonstrable with culture supernatants from Fc-receptor-negative endothelial cells. To more completely determine that monocyte supernatants contained shed Fc receptors, inhibition of direct Fc rosettes by the same supernatants was demonstrated. The supernatants are most active for Fc receptor activity after monocytes are cultured for 7–9 days. The activity of Fc receptor material varied among donors. Monocyte culture supernatants may be utilized as sources of monocyte Fc receptor material for future evaluation.