Growth factors expressed at the fetal-maternal interface modulate hormone expression of placental trophoblasts. The aim of this study was to investigate the effects of different cytokines on hCG subunit mRNA expression in differentiating villous cytotrophoblasts. Quantitative real-time PCR revealed a 1.8- and 6.9-fold increase of hCG-I? and hCG-I? mRNA levels, respectively, between 36 and 60 h of term trophoblast syncytialization. Compared with controls, neither interleukin (IL)-1I?, IL-2, IL-4, IL-6, IL-10, IL-13 and IL-15 nor tumour necrosis factor (TNF)-I? significantly altered hCG-I? mRNA expression. Similarly, the ILs did not affect hCG-I? transcript levels. In contrast, TNF-I? suppressed hCG-I? mRNA 3.8- and 1.8-fold at 36 and 60 h of term trophoblast differentiation. Accordingly, hCG secretion was impaired by TNF-I? but not by the different ILs. Moreover, TNF-I? reduced luciferase expression of reporter plasmids harbouring the proximal hCG-I?5 promoter to 35 and 77 , respectively, in primary term trophoblasts and trophoblastic SHGPL-5 cells. In addition, counting of nuclei in syncytialized, desmoplakin-negative areas revealed a 1.9-fold reduction of term trophoblast fusion in the presence of TNF-I?. Similarly, floating explant cultures prepared from first trimester-denuded villi recovered the syncytium 2.8-fold less efficiently during 72 h of cytokine treatment. Concomitantly, TNF-I? impaired induction of endogenous and secreted hCG-I? protein levels in these cultures. The data suggest that TNF-I? decreases hCG-I? mRNA and protein expression by reducing gene transcription and trophoblast cell fusion. Suppression of these processes by TNF-I? could partly explain the adverse effects of the cytokine on placental function and pregnancy outcome. A? 2006 Oxford University Press.