Human placental cells that regulate lymphocyte function.

We examined normal human placenta for an immunologic function by measuring the release of soluble inhibitory factor (SIF). SIF is a product of normal T lymphocytes and of the JEG-3 choriocarcinoma cell line, and blocks proliferative and antibody-producing responses of mononuclear cells. SIF can be further characterized by a noncovalently linked subcomponent, lipid suppressor substance. The villous surfaces of six normal human placentae were digested with collagenase to obtain a population of predominantly multinucleated giant cells. These cells were maintained in standard culture for 5 days after which the cell-free conditioned culture medium was assayed for SIF content by measuring suppression of [3H]thymidine incorporation into lymphocytes stimulated by low-dose phytohemagglutinin. Undiluted placental SIF induced 88% inhibition of this response (p less than 0.001). The placental SIF was found to contain lipid suppressor substance, as does SIF from mononuclear cells. We determined this by thin-layer chromatography where a peak of suppressive activity occurred at Rf 0.32 [( 3H]thymidine incorporation reduced from 21810 +/- 308 to 4121 +/- 214 cpm); this is the position on thin-layer chromatography to which mononuclear cell lipid suppressor substance migrates. Ion exchange chromatography comparing the elution patterns of lymphocyte-SIF and placental-SIF indicated that both eluted in the fraction of 40-50 mM PO4 means buffer, further suggesting identity between these two substances. SIF from placental and lymphocyte sources functioned by inducing the presence of suppressor cells in culture.(ABSTRACT TRUNCATED AT 250 WORDS)