TUMOUR NECROSIS FACTOR  BINDING TO HUMAN AND MOUSE TROPHOBLAST Edith Ben-Yair, 1 Amir Less, 2 Silvia Lev, 3 Liat Ben-Yehoshua, 1 Boris Tartakovsky 1,4 Tumour necrosis factor  (TNF-) is a cytokine with pleiotropic effects, modulating cell growth, differentiation, and synthesis of various substances. Recent demonstration of TNF- mRNA and protein in the uteroplacental unit suggests that this cytokine may be involved in the development of the embryo. To determine whether the embryo itself binds TNF-, mouse blastocyst outgrowths and human first trimester villous trophoblast were analysed for TNF- binding. Our experiments revealed that binding of TNF- could be specifically detected on the trophectoderm of the outgrowing mouse embryos. They also show a complete disappearance of the colony-stimulating factor 1 (CSF-1) receptor that occurs shortly after the binding of TNF- by the trophectoderm. In human first trimester villous trophoblast, TNF- binding was found to be predominantly detectable on the syncytiotrophoblast and to a lesser extent on the cytotrophoblastic cells. Binding was not observed on adjacent embryonic or maternal cells. Our results further support the idea that TNF- as well as other cytokines may modulate early embryonic development and implantation.  1997 Academic Press Limited During gestation, the embryo undergoes complex morphogenetic changes that transform it into a recognizable individual. Although this is one of the most fundamental events in biology, very little is known about the mechanisms enabling it to proceed normally. At pre-implantation, the mammalian developing embryo is subjected to two regulatory systems: its own genetic information and programmed development on one hand and its maternal specialized environment in the oviduct and uterus on the other hand. Obviously, the successfully synchronized sequence of events, culminates at the point where a hatched blastocyst is able to implant properly into a carefully prepared receptive endometrium. Numerous factors are appar- ently involved in regulating these processes. One group of factors that has been recently found to have important functions in almost any biological system consists of the soluble or cell bound cytokines. The cytokine family is a large and ever-expanding group of polypeptides that includes the interleukins (IL), tumour necrosis factors (TNF)  and , colony- stimulating factors (CSFs), interferons and others. They have numerous and diverse actions on many cell types. In recent years, evidence has accumulated demonstrating that cytokines may also be involved in pregnancy, 1 being capable of modulating early embryonic development, 2 implantation 3 and even delivery. 4,5 In the present study, we focused on TNF-. Contradicting activities have been assigned to this molecule: for example, Gendron et al . 6 reported that lipopolysaccharide-induced fetal resorption was associ- ated with intrauterine production of TNF-; Chaouat et al . 7 also showed that TNF- administration during pregnancy increased fetal resorption in the CBA/ JXDBA/2 mating. In contrast, we reported in a previous study that the pregnancy blocking effect of CSF-1 could be fully counteracted by TNF- and that very small quantities of TNF- could also prevent pre-implantation defects found in the CSF-1 induced model and in the CBA/JXDBA/2 mating. 2 Thus, the effect of TNF-, either positive or negative in pregnancy, remains to be determined. TNF- is a 17-kDa polypeptide originally identified as a product of activated macrophages that inhibited tumour cells proliferation. 8 TNF- is now known to be produced by other cell types 9 and to possess pleiotropic effects, modulating cellular growth, differentiation and synthesis of various substances. 10 Still, its specific role in development is not clear. The purpose of this study was to examine TNF- binding to mouse and human trophoblast, at the earliest feasible stage of implantation. From the 1 Department of Chemical Immunology, The Weizmann Institute of Science Rehovot, 2 Departments of Obstetrics and Gynecology; and 3 Pathology, Meir Hospital, Kfar Saba, Israel, 4 Present address: Clinical Immunology Unit, Sourasky Medical Center, 6 Weizman St. Tel-Aviv, 64239, Israel Correspondence to: Edith Ben-Yair, Dept. Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel Received 6 September 1996, revised and accepted for publication 12 May 1997  1997 Academic Press Limited 1043–4666/97/110830 + 7 $25.00/0/ck970236 KEY WORDS: CSF-1/implantation/placenta/TNF-/trophoblast CYTOKINE, Vol. 9, No. 11 (November), 1997: pp 830–836 830