BOVINE LACTOFERRIN STIMULATES THE PHAGOCYTIC-ACTIVITY OF HUMAN NEUTROPHILS - IDENTIFICATION OF ITS ACTIVE DOMAIN

Bovine LF (bLF) at concentrations in the range of 50-250 mu g/ml enhan ced the phagocytic activity of human neutrophils as determined by meas uring the incorporation of FITC-labeled latex beads by flow cytometry. The stimulatory effect of bLF was not abrogated by hydrolysis with pe psin. Bovine lactoferricin (bLFcin), which is a bactericidal fragment purified from a pepsin hydrolysate of bLF (bLFH), also enhanced the ph agocytic activity, whereas, in contrast, the fraction of bLFH depleted of bLFcin showed no stimulatory effect. The phagocytosis-enhancing ac tivity of bLF still remained after washing the neutrophils, following exposure to bLF. Also, bLF pretreatment of the latex beads stimulated their uptake. These results demonstrate that bLF is effective in promo ting the phagocytic activity of human neutrophils. This activity appea rs to be due to its bLFcin domain and may involve dual mechanisms of d irect binding to neutrophils and opsonin-like activity. (C) 1998 Acade mic Press.