Paf‐acether (platelet‐activating factor) is a phospholipid initially described as a potent platelet‐aggregating compound. It is produced by numerous cell types and is now considered as an important mediator of cell‐cell interactions. The effect of paf‐acether on the expression of CD2 and CD3, two human T cell surface glycoproteins, was investigated by indirect immunofluorescence and flow cytometry. Paf‐acether partially down‐regulated, in a time‐ and dose‐dependent manner, CD2 and CD3 but not HLA class I antigen expression on peripheral human T cells and Jurkat cells. Lysophosphatidylcholine, a phospholipid closely related to paf‐acether, had no detectable modulatory effect on CD2 and CD3 expression. In addition to CD2/CD3 modulation, pafacether markedly inhibited T cell proliferative response not only to phytohemagglutinin or concanavalin A but also to anti‐CD3 or a stimulatory combination of anti‐CD2 monoclonal antibodies. These data demonstrate for the first time that lipid mediators such as paf‐acether might be involved in the regulation of the expression of cell surface glycoproteins that are essential in the execution of T cell function.
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