LIPOPOLYSACCHARIDE-INACTIVATING ACTIVITY OF NEUTROPHILS IS DUE TO LACTOFERRIN

Neutrophils can inactivate lipopolysaccharide (LPS), thereby blocking the ability of LPS to prime fresh neutrophils for enhanced fMLP-trigge red release of superoxide. Here we show that inactivation of LPS by ne utrophils was primarily due to lactoferrin. A time course for inactiva ting LPS showed that neutrophils (5 million/ml) took 30 min to inactiv ate 10 ng/ml LPS. Mononuclear cells could not inactivate LPS under the same conditions, Experiments with radioactive LPS showed that inactiv ated LPS remained in the medium and was not taken up or destroyed by t he neutrophils during inactivation, Inactivated LPS still gelled Limul us lysate and primed monocytes, Cell-free medium from neutrophil suspe nsions also inactivated LPS. A single LPS-inactivating factor was puri fied from medium by heparin-agarose chromatography. SDS-PAGE showed a single band at 80 kDa, which was identified as lactoferrin by immunobl otting, Antilactoferrin immunoglobulin G removed the LPS-inactivating activity from purified lactoferrin and cell-free medium, Surprisingly, even purified neutrophil lactoferrin required 30 min to inactivate LP S, indicating inherently slow binding of lactoferrin to LPS.