Abstract: 　Objective To study the possible mechanism of CD4~+ T cells deletion in mice with alveolar echinococco- sis, particularly on the relationship between Echinococcus multilocularis infection and apoptosis of T lymphocyte subsets. Methods BALB/c mice were infected with E. multilocularis and uninfected mice were used as control group. CD4~+ T cell and CD8~+ T cells were separated 12 weeks and 25 weeks after infection. Purified CD4~+ and CD8~+ T cell subsets were cul- tured in complete medium and stimulated with EmAg, anti-CD3 mAb, rIL-2, mouse rTNFα and PWM respectively. After 16 h of incubation, cells were collected and assessed by electron microscopy. DNA fragmentation was observed by eletrophoresis, stained by TUNEL assays and PI, analyzed by flow cytometry. Results CD4~+ and CD8~+ T cells in 25 weeks experiment group presented chromatin condensation, lost nuclear membrane integrity, and formed exocytoplasmic vacuolization. DNA ladder was observed by agarose gel eletrophoresis, and the appearance of DNA fragments was equiva- lent to approximately 200 bp. None of these appearances were observed in control group in 12 weeks post infection and CD8~+ T cell in mice of 25 weeks post infection group. The apoptosis level of CD4~+ and CD8~+ T cells in 12 weeks post infec- tion group was not significantly different from the control group. While the apoptosis level of CD4~+ and CD8~+ T cells in- creased significantly in 25 weeks post infection group as compared with the control (P<0. 01). Higher apoptosis in CD4~+ T cells was observed than that of CD8~+ T cells. Apoptosis mainly appeared during S phase of cell cycle. Conclusion Apoptosis is a prominent causation of activation-induced CD4~+ T cell death in later period of E. multilocularis infection. In- crease of the death-promoter signals and decrease of the death suppresser signals may have been responsible, in part, for the apoptosis in CD4~+ T lymphocytes in the infected mice.

Key words: Echinococcus multilocularis, AICD, CD4~+ T cells, apoptosis