Platelet-activating factor stimulates cytokine production by human endometrial stromal cells

Although preimplantation embryo and decidual cells secrete significant amounts of platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF); its precise function in early pregnancy has yet to be established. To investigate the effect of PAF on cytokine synthesis, we measured the cytokine concentration in the culture media of two human cell lines: normal endometrial stromal cells (ESC) and endometrial stromal sarcoma cells (MaMi), following stimulation with a non-metabolized PAF analogue, carbamyl-PAF (C-PAF). Enzyme-linked immunosorbent assays were used to measure five cytokines: interleukin (IL)-6, IL-8, macrophage colony-stimulating factor (M-CSF), macrophage inflammatory protein-1alpha (MIP-1alpha) and tumour necrosis factor-alpha (TNF-alpha). We also evaluated the mRNA expression for IL-6 and IL-8 in ESC after C-PAF stimulation using Northern blot analysis. Non-stimulated ESC and MaMi cells both secreted IL-6, IL-8, and M-CSF, but not MIP-1alpha or TNF-alpha. The concentrations of IL-6, IL-8, M-CSF, MIP-1alpha, and TNF-alpha in the culture media of both cell lines increased in parallel with increasing amounts of C-PAF. C-PAF stimulated IL-6 and IL-8 transcription in ESC. These results suggest that PAF secretion by decidual tissues and developing embryos may induce cytokine synthesis by the ESC, as part of the cytokine network in the feto-maternal unit. An increase in the local cytokine concentration may be an important factor in the maintenance of early stages of gestation.