Lipid and protein components of the syncytiotrophoblast plasma membrane inhibit lymphocyte proliferation by two distinct pathways

The ability of syncytiotrophoblast plasma membrane lipid and protein fractions (STPM lipids, STPM proteins), tested under a reconstituted form, to inhibit lymphocyte proliferation induced by PHA was investigated. The cytostatic activity of STPM proteins appeared greater than that of the STPM lipids. Furthermore, IL-2 production and IL-2 receptor expression by activated lymphocytes were markedly decreased in the presence of STPM proteins compared to the native membrane but remained unaffected in the presence of STPM lipids. Finally, the inhibition of lymphoproliferation could be maintained after removal of the protein fraction from lymphocytes prior to stimulation by PHA. The biological and immunological significance of these results is discussed.