Abstract: Objective  To study the expression of Smads proteins involved in TGF-β1 signal transduction during the process of liver fibrosis in BALB/c mice infected with Schistosoma japoncum.  Methods  Thirty-four BALB/c mice were each infected with （20±1） S. japonicum cercariae. The mice were sacrificed at 8, 12, 16 and 24 weeks post-infection. Ten healthy BALB/c mice served as normal control group. The liver tissues were fixed in 10% formaldehyde for histology and immunohistochemistry assay. The single-egg granuloma area was measured in hematoxylin-eosin stain section. The degree of liver fibrosis was determined by Sirius red staining. Immunohistochemistry was used to observe the expression of Smad protein.  Results  The area of single-egg granuloma peaked at 8th week post-infection ［（5.33±1.03） mm2］, and with time passing, the area diminished, and the area of granuloma reduced to（2.94±1.69）mm2 at 24 weeks post-infection. The difference was significant among the 4 periods after infection in single-egg granuloma area（P<0.05）. Collagen fibers appeared around granulomas at 8 weeks （2.03±0.52） and increased gradually. At 24 weeks post-infection, the degree of liver fibrosis reached a peak（6.90±1.57）, and the liver fibrosis degree was significantly different among infection groups（P<0.05）. Immunohistochemistry showed low expression level of Smad2/3 and Smad7 and inconspicuous level of Smad4 in livers of the normal mice. The expression of Smad2/3 was found mostly in the cytoplasm and nucleus of cells around granulomas at 8th week post-infection, and the positive area of Smad2/3 was （7.24±1.64）% by semi-quantity. At 12 weeks post-infection, the Smad2/3 protein expression level around granulomas and liver sinus reached the peak［（10.01±1.07） %］, and there was significant difference between infection groups and the control [(2.13±0.32）%]. A significant difference in the Smad2/3 protein expression level was found between 12 weeks post-infection group and 8 weeks or 16 weeks post-infection groups. The expression level of Smad4 was（8.81±1.13）% at 8th week post-infection, higher than that in the control［（4.83±1.15）%］（P<0.05）. There was no difference among the infected mice at different periods in the level of Smad4（P>0.05）. After 8 weeks post infection, Smad7 protein sparsely appeared around the granuloma ［（4.15±1.26）%］ while it disappeared around liver sinus. At 12 weeks post-infection, the level of Smad7 protein was higher［（6.34±1.5）%］, but with prolonged infection time， no significant difference was revealed （P>0.05）. The level of Smad7 in infected mice was higher than that in the control（P<0.05）.  Conclusion  Results show high expression for Smad2/3 and Smad7 and low expression level of Smad4 during the process of liver fibrosis in BALB/c mice infected with Schistosoma japoncum.

Key words: Schistosomiasis japonica, Egg granuloma, Liver fibrosis, Smad protein