Abstract:

Objective  To investigate the effect of lipopolysaccharide（LPS）-induced B cell activation on the development of Schistosoma japonicum.  Methods  Eighteen BALB/c nude mice deficient in T cells and 23 BALB/c SCID mice deficient in T and B cells were used in this study. Each was infected with 30±1 S. japonicum cercariae. The nude （n=9, NL group） and SCID（n=12, SL group） mice then received 2-3（every two weeks） intraperitoneal injections with LPS （100 μg/mL, 0.2 mL for each mouse）. The remaining nude（n=9, N group） and SCID（n=11, S group） mice received PBS injection as control. The mice were sacrificed on days 28 and 36 after infection（n=4/5, 4/5, 5/6, 6/6 for N, NL, S and SL groups, respectively）, and adult worms were collected by hepatic portal vein perfusion. The collecting rate of the adult worms was calculated, the body-length measured, and pairs of worms recorded. The liver tissue was collected and digested with 5% KOH, and the number of eggs per gram of liver tissue was calculated. The levels of TGF-β, IFN-γ and IL-10 in peripheral blood were evaluated. Spleen cell suspension was prepared for detecting the proportion of regulatory B cells（Bregs） in splenic lymphocytes.  Results  On day 28 after infection, the body-lengths of male worms in NL and N groups were (7.65±2.85) mm and (5.28±1.64) mm （P<0.01）, and those of female worms were (9.64±1.99) mm and (7.49±1.63) mm （P<0.01）, respectively. On day 36 after infection, the number of eggs per gram of liver tissue was significantly higher in the NL group than in the N group（1 088±297 vs 715±404, P<0.05）, and significantly lower in the SL group than in the S group（217±33 vs 573±160, P<0.01）. The proportions of CD1dhiCD5+CD19+ Bregs in N group on days 28 and 36 after infection were（12.73±0.96）% and（37.15±3.04）% （P<0.05）, respectively, with no significant difference with that of NL group. The serum levels of TGF-β and IFN-γ on day 28 after infection were significantly different between N and NL groups（TGF-β, 101.75±46.72 vs 260.90±45.34 pg/mL; IFN-γ, 7.91±1.62 vs 14.11±3.72 pg/mL, both P<0.01）. Similarly, significant difference was found for the plasma level of IL-10 on day 36 after infection between the S and N groups （41.85±3.14 vs 66.25±4.16 pg/mL, P<0.01）, and between the SL and NL groups （44.48±3.87 vs 72.22±17.76 pg/mL, P<0.01）, but not between the LPS groups and the control groups.  Conclusion  LPS can induce the release of cytokines （e.g. TGF-β） from B cells of mice infected with S. japonium, to facilitate the early development of adult female and male worms.

Key words: Schistosoma japonicum, B lymphocyte, Breg, IL-10, TGF-β, INF-γ