Surface and cell membrane activities of leukocyte chemotactic factors

Abstract

PROTEINS with an affinity for air–water interfaces may also show an affinity for hydrophobic sites in cell membranes. In exploring the basis for recognition in leukocyte chemotaxis, I and my colleagues have previously reported that proteins which excite a locomotor response in leukocytes do so by virtue of their possession of externally positioned nonpolar groups^1–3. A protein may possess such groups either because it has become denatured, because nonpolar groups have been conjugated to it, or because, like α_s- or β-caseins, its intrinsic content of nonpolar residues is too high for them all to be packed internally⁴. These proteins would be expected to be surface active and could possibly penetrate the phospholipid bilayer of a leukocyte to activate the cell for chemotaxis in a way that a more hydrophilic protein could not. This paper presents evidence that the surface activity and the chemotactic activity of proteins are indeed related, and that the chemotactic response of the leukocyte can be modified using membrane-active enzymes such as phospholipase A. These findings support the suggestion that chemotactic factors interact with the phospholipid bilayer of the cell membrane.