BACKGROUND AND PRESENT STATUS OF RESEARCH ON PLATELET‐ACTIVATING FACTOR (PAF‐ACETHER)

A leukocyte-dependent mechanism capable of releasing histamine from platelets was first reported in 1966, and a soluble principal intermediate between rabbit leukocytes and platelets was detected in 1971.’e2 It was at that time described as “lytic” and was not characterized. One of us described the methodology for obtaining this substance routinely, started its characterization, named it platelet-activating factor (PAF), and showed that it was released from rabbit basophils through an IgE-dependent proces~ .~ Its presence was subsequently demonstrated in human leukocytes, and aggregation and the release reaction were shown for human platelet^.^ Finally, most of its known physicochemical characteristics, including its phospholipid nature, were described (see refs. in 5) . At this stage, we knew that PAF was a glycerophospholipid with a choline polar head group, an ester-linked acyl chain on the carbon 2, and no ester link at the carbon 1 position.6 A new class of phospholipid mediator was therefore proposed. Finally, the structure of the mediator was elucidated (FIG. 1 ) as being 1 -O-alkyl-2-acetyl-glyceryl-3-phosphorylcholine, and its total synthesis was achieved.’-g PAF is therefore now termed PAFacether, since it is an ether-lipid and has an acetate residue. We think it is preferable to keep to the established name, and not to replace it by the initials of the now recognized chemical name, in order to preserve a link with previous accomplishments and reduce literature confusion. For similar reasons prostaglandins or heparin, for instance, were not renamed when structures became available. Given the numerous substances present in biological fluids and cell supernatants that can activate platelets, it was necessary to define PAF-acether strictly. Even before knowing its structure, we used the following criteria to distinguish it from arachidonic acid, thrombin, ADP or prostaglandins: