Abstract: Objective   To investigate the effect of ageing on the immune responses against Schistosoma japonicum infection in mice.   Methods   Female BALB/c mice were divided into young group （2 months） and old group （18 months）, each composed of 8 mice. Each mouse was percutaneously infected with 40±1 S. japonicum cercariae. At 6 weeks post-infection, the mice were sacrificed, and the spleens were removed and single-cell suspensions of splenocytes were prepared. Worms were perfused from hepatic portal system and counted. The number of eggs in the liver was determined after KOH digestion. Mean single-egg granulomas sizes were determined in stained histological sections. Splenocyte proliferation responses were analyzed by MTT colorimetry. Level of interferon-γ （IFN-γ） and interleukin-4 （IL-4） in the splenocyte culture supernatants was determined by ELISA.   Results   The worm burden and egg per gram of liver in old mice ［19.75±1.95, （1.59±1.05）×10⁴］ were significantly lower than that of young mice [26.00±2.42, （2.08±0.87）×10⁴］ （P＜0.05）. The mean volume of single-egg granulomas of the livers in old mice ［（30.13±10.97） ×10^-3 mm³］ was significantly lower than that of the young mice ［（47.02±24.13） ×10^-3 mm³］ （P＜0.05）.  Results of T cell proliferation showed that the splenocytes had poorer immune reactivity to ConA in old mice （SI： 1.08±0.12） than that in young mice （SI： 1.31±0.14） （P＜0.05）. Levels of IFN-γ and IL-4 in the splenocyte culture supernatants [（24.05±6.24)， (4.15±0.68) pg/ml] from old mice were lower than that of young mice [（34.25±8.69)， (7.25±0.83) pg/ml]（P＜0.05）.   Conclusion   Ageing down-modulates the immune responses and the poorer immune reactivity might decrease pathological alterations in mice infected with Schistosoma japonicum.

Key words: Ageing, Mouse, Schistosoma japonicum, Immune response