[Exhaustion of CD8+ T cell immune functions in spleen of mice with different doses of Echinococcus multilocularis infections].

OBJECTIVE: To examine the changes in the immune functions of CD8+ T cells in the spleen of mice following Echinococcus multilocularis infections at various doses and at different time points. METHODS: The E. multilocularis protoscoleces were collected, and E. multilocularis infection was modeled in mice via the hepatic portal vein at doses of 50 (low-dose), 500 (medium-dose) and 2 000 protoscoleces (high-dose), while physiological saline served as controls. Mouse spleen was isolated 2 (earlystage), 12 (middle-stage) and 24 weeks post-infection (late-stage), and spleen lymphocytes were harvested. The phenotype of memory CD8+ T cells and 2B4 expression were quantified in the mouse spleen, and the secretion of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-17A and IL-10 was measured. RESULTS: A central-memory phenotype was predominant in the CD8+ T cells in the spleen of mice at the early stage of high-dose protoscolece infections, and the proportion of central-memory CD8+ T cells was significantly greater in the high-dose group than in the control group (35.50% ± 2.00% vs. 25.90% ± 2.46%, P < 0.01), while a effector- memory phenotype was predominant in the CD8+ T cells in the spleen of mice at the late stage of medium- and high-dose protoscolece infections, and the proportions of effector-memory CD8+ T cells were significantly greater in the medium- (25.70% ± 4.12%) and high-dose group (28.40% ± 4.12%) than in the control group (10.50% ± 6.45%) (P < 0.05). The proportions of the central-memory CD8+ T cells were significantly higher in the high-dose group than at middle and late stages than at the early stage (P < 0.01), and the proportion of effector-memory CD8+ T cells was significantly greater in the high-dose group at the late stage than at early and middle stages (P < 0.05). The secretion of IFN-γ and IL-17A by spleen CD8+ T cells was elevated in the low- and medium-dose groups at the early stage of infection, and high-dose protoscolece infection promoted the secretion of IFN-γ and TNF-α by spleen CD8+ T cells; however, the levels of IFN-γ and TNF-α were significantly lower at the late stage than at the early and middle stages (P < 0.05). In addition, high 2B4 expression was detected in spleen CD8+ T cells in the middle- and high-dose groups at the late stage of infection, and the 2B4 expression was significantly higher in the medium(4.73% ± 1.56%) and high-dose groups (4.94% ± 1.90%) than in the low-dose group (2.49% ± 0.58%) and the control group (2.92% ± 0.60%) (P < 0.05). CONCLUSIONS: E. multilocularis may be killed and eliminated through the host immune responses at the middle and late stages of low- and medium-dose protoscolece infections, while high-dose protoscolece infections may trigger the upregulation of 2B4 expression in mouse spleen CD8+ T cells at the late stage, which leads to immune exhaustion and the resultant chronic infections.