Human leukocyte elastase, cathepsin G, and lactoferrin: family of neutrophil granule glycoproteins that bind to an alveolar macrophage receptor.

Interactions between polymorphonuclear neutrophils and mononuclear phagocytes are potentially of great importance in a variety of inflammatory processes. As part of a continuing effort to elucidate the physiologic importance of human alveolar macrophage receptor-mediated binding of neutrophil (leukocyte) elastase, I have studied the binding of leukocyte elastase and two other neutrophil granule glycoproteins, cathepsin G and lactoferrin, to human alveolar macrophages. Saturable binding of all three ligands at 0 degrees C was observed, with equilibrium dissociation constants of 4.0 x 10(-7), 2.0 x 10(-7), and 1.7 x 10(-6) M, respectively. All bound to a similar number (54-73 x 10(6)) of sites per cell. Binding of all three ligands was inhibited by the polysaccharide fucoidin, and extensive cross-inhibition of their binding to macrophages was observed. The results indicate that alveolar macrophages possess a relatively low-affinity, high-volume receptor for a family of neutrophil granule glycoproteins, which would be ideally suited for clearing released neutrophil granule contents from the extracellular space in inflamed tissues.