In vitro and in vivo inhibition of monocyte phagocytic function by factor VIII concentrates: correlation with concentrate purity

S ummary . Seven factor VIII concentrates of varying purity (specific activity 0.67–10 units factor VIII procoagulant activity (VIII: C)/mg protein) have been examined over a range of concentrations (0.5–0.005 u/ml factor VIII) to establish their effect on in vitro monocyte phagocytic function. All these products inhibited monocyte phagocytic function, but the monoclonally purified product tested was significantly less inhibitory than the others ( P <0.05). The degree of inhibition observed was independent of the virus inactivation method used to increase product safety. However, comparison of three products of differing purity from the same manufacturer showed that the inhibitory effect decreased as product purity increased. In vivo studies of monocyte function following infusion of two of these factor VIII concentrates demonstrated inhibition of circulating monocytes. The possible role of product purity in modulating immune responses in haemophiliacs is discussed.