SPECIFIC BINDING BY HUMAN POLYMORPHONUCLEAR LEUKOCYTES OF THE IMMUNOLOGICAL MEDIATOR 1-O-HEXADECYL OCTADECYL-2-ACETYL-SN-GLYCERO-3-PHOSPHORYLCHOLINE

Abstract

The binding of the platelet-activating factor 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine (AGEPC) by human polymorphonuclear (PMN) leukocytes was complete within 20-230 min and optimal at 37.degree. C. Scatchard plot analyses of the total binding of [3H]AGEPC by PMN leukocytes without and with an excess of unlabeled AGEPC revealed 2 distinct types of binding sites. One type of binding site exhibited a high affinity (Kd = 0.11 .+-. 0.02 nM, mean .+-. SD), was saturable and had a maximal capacity of 5.2 .+-. 2.1 .times. 106 (mean .+-. SD) molecules of AGEPC/PMN leukocyte. The other binding site demonstrated a substantially lower binding affinity and a greater binding capacity consistent with nonreceptor uptake of AGEPC into cellular structures. The high affinity binding site of PMN leukocytes in suspension was saturated at 196 .+-. 90 pmol (mean .+-. SD) of AGEPC/ml, while 600 pmol of AGEPC/ml evoked maximal PMN leukocyte chemotaxis in modified Boyden chambers. The specificity of binding of AGEPC by PMN leukocytes was established by the capacity of analogs of AGEPC, but not structurally distinct chemotactic factors, to inhibit the binding of [3H]AGEPC. The high affinity PMN leukocyte binding site for AGEPC was specific for a phospholipid with an .alpha.-ether linkage and a .beta.-short chain fatty acid, but the binding site lacked stereospecificity. Similar structural requirements were observed for the elicitation of PMN leukocyte chemotaxis and the enhancement of the expression of PMN leukocyte complement component C3b receptors by AGEPC.