Background Enhanced apoptosis of cytotrophoblasts in early pregnancy is associated with high risk of intrauterinegrowth retardation and preeclampsia,which are two common pregnant complications.Its etiological factors remainunclear.Cytotrophoblasts share some traits with innate immune cells and may show response to lipopolysaccharide.Thisstudy was conducted to demonstrate whether lipopolysaccharide has apoptosis-inducing effects on cytotrophoblast andthe role of innate immune reaction in this process.Methods Cytotrophoblasts were isolated from early pregnant villous tissues and cultured with serum-free medium.Subsequently,cytotrophoblasts were treated with lipopolysaccharide at the concentrations of 0(control),25,50,100 and200 ng/ml for 24 hours.Apoptosis of cytotrophoblasts was determined by light microscopy,Hoechst 33258 DNA stainingwith a fluorescent microscope,transmission electron microscope and annexin V-fluorescein isothiocyanate-conjugated /propidium iodide(PI)staining with flow cytometry.Then expression of caspase-3 was detected by Western blot.Confocalimmunofluorescence technique was used to detect tumor necrosis factor a expression in cytotrophoblasts.The levels oftumor necrosis factor a in the culture medium were detected by enzyme-linked immunosorbent assay.Results Under light,fluorescence microscope and transmission electron microscope,characteristic alternations ofapoptosis in cytotrophoblasts were observed after lipopolysaccharide treatment.Flow cytometry results showed thatlipopolysaccharide significantly increased apoptosis indexes of cytotrophoblasts.Significant statistical differences werefound in the above groups(P≤0.01).The mean relative densities of bands corresponding to caspase-3 weresignificantly increased in groups treated with lipopolysaccharide,as compared with the normal control(P<0.001).Tumornecrosis factor a expression was found to increase in cytotrophoblasts by confocal immunofluorescence technique and inculture medium by enzyme-linked immunosorbent assay after lipopolysaccharide treatment.A positive correlation wasfound between tumor necrosis factor a expression and apoptosis indexes of cytotrophoblasts(r=0.747,P<0.001).Conclusion Apoptosis of cytotrophoblasts could be induced by lipopolysaccharide,in which innate immune reaction isthe important mechanism. Background Enhanced apoptosis of cytotrophoblasts in early pregnancy is associated with high risk of intrauterine growth retardation and preeclampsia, which are two common pregnant complications. Its etiological factors remainunclear. Cytotrophoblasts share some traits with innate immune cells and may show response to lipopolysaccharide. This study was conducted to demonstrate whether lipopolysaccharide has apoptosis-inducing effects on cytotrophoblast and the role of innate immune reaction in this process. Methods Cytotrophoblasts were isolated from early pregnant villous tissues and cultured with serum-free medium. Substituted, cytotrophoblasts were treated with lipopolysaccharide at the concentrations of 0 ( control, 25, 50, 100 and 200 ng / ml for 24 hours. Apoptosis of cytotrophoblasts was determined by light microscopy, Hoechst 33258 DNA staining with a fluorescent microscope, transmission electron microscope and annexin V-fluorescein isothiocyanate-conjugated / propidium iodide flow cytometry. Expression of caspase-3 was detected by Western blot. Confocalimmunofluorescence technique was used to detect tumor necrosis factor a expression in cytotrophoblasts. The levels of tumor necrosis factor a in the culture medium were detected by enzyme-linked immunosorbent assay. Results Under light , fluorescence microscope and transmission electron microscope, characteristic alternations ofapoptosis in cytotrophoblasts were observed after lipopolysaccharide treatment. Flow cytometry results showed that lipopolysaccharide significantly increased apoptosis indexes of cytotrophoblasts. Statisticalant statistical differences were found in the above groups (P≤0.01). The mean relative densities of bands corresponding to caspase-3 weresignificantly increased in groups treated with lipopolysaccharide, as compared with the normal control (P <0.001). Tumornecrosis factor a expression was found to increase in cytotrophoblasts by confocal immunofluorescence technique and inculture medium by enzyme-li nked immunosorbent assay after lipopolysaccharide treatment. A positive correlation was found between tumor necrosis factor a expression and apoptosis indexes of cytotrophoblasts (r = 0.747, P <0.001) .Conclusion Apoptosis of cytotrophoblasts could be induced by lipopolysaccharide, in which innate immune reaction is the important mechanism .