关键词: 伯氏疟原虫, 程序性死亡受体-1, 固有免疫, 细胞免疫

Abstract:

Objective To investigate the effect of programmed cell death-1(PD-1) blockade on immune responses to the infection of Plasmodium berghei ANKA (PbA) in mice.Methods BALB/c mice were divided by random number table method into 3 groups: the healthy group, infection group and PD-1 group, 8 mice each. Mice in the infection group and PD-1 group were injected intraperitoneally with 1 × 10⁶ PbA-infected red blood cells, while those in the healthy group did not receive any treatment. On the day of infection and on days 3, 5, and 7 after infection, mice in the PD-1 group were injected intraperitoneally with 200 μg of PD-1 monoclonal antibody, while the infection group was injected with equal dose of PD-1 homotype control monoclonal antibody. The erythrocyte infection rate and mice survival rate were monitored every other day from day 4 after infection. On day 5 after infection, 4 mice in each group were sacrificed. Spleen tissues were collected to prepare spleen cell suspensions. Myeloid dendritic cells (mDCs) and the expression of PD-1 ligand (PD-L1) in spleen cells, as well as the percentages and absolute numbers of bone marrow-derived inhibitory cells (myeloid-derived suppressor cells, MDSCs) and Th1 cells were detected by flow cytometry. IFN-γ, IL-6 and IL-10 levels in spleen cell culture supernatant were determined by ELISA.Results In the infection group, Plasmodium-infected red blood cells began to appear in peripheral blood 5-6 days after infection, and then the infection rate of red blood cells increased rapidly, reaching about 40% on day 16 after infection, but there was no difference between the PD-1 group and the infection group. In the infection group, deaths occurred from day 15 after infection and all died by day 23 after infection. In the PD-1 group, deaths occurred from day 13 and all died by day 18. Flow cytometry showed that the percentage of CD11c⁺CD11b⁺ mDCs in PD-1 group was (2.21 ± 0.10)%, which was significantly lower than that in the infection group [(4.51 ± 0.21)%, P < 0.05]; the percentage of CD4⁺T-bet⁺IFN-γ⁺ Th1 cells [(3.38 ± 0.54)%] was also lower than that in the infection group [(5.85 ± 0.42)%, P < 0.05]. The expression of PD-L1 on mDCs was higher in PD-1 group [(55.6 ± 6.35)%] than that in the infection group [(21.35 ± 4.45)%, P < 0.05]. The percentage of Gr-1⁺CD11b⁺ MDSCs in the PD-1 group [(9.03 ± 0.62)%] was higher than that in the infection group [(3.58 ± 0.16%), P < 0.05]. The levels of IFN-γ, IL-6 and IL-10 in the infection group were (901.69 ± 73.37) pg/ml, (200.94 ± 4.97) pg/ml and (551.95 ± 121.71) pg/ml, respectively, while those in the PD-1 group were (231.17 ± 57.69) pg/ml, (86.1 ± 3.93) pg/ml and (101.72 ± 20.73) pg/ml, respectively.Conclusion PD-1 blockade weakened the protective immune response to PbA infection in mice.

Key words: Plasmodium berghei, Programmed cell death-1, Innate immunity, Cellular immunity