[The ratio of Treg/Thl7 cells from mice infected with Plasmodium yoelii in the early stage of infection].

Objective: To investigate the change of Treg/Th17 cell ratio in mice infected with Plasmodium yoelii 17XL in the early stage of infection.

Methods: Forty 6-8 week-old female BALB/c mice were randomly divided into infection group and Treg blockade group. All the mice were infected by intraperitoneal injection with 1 x 10(6) P. yoelii 17XL-parasitized erythrocytes. Mice in Treg blockade group were intraperitoneally injected with 1 mg CD25 mAb before infection and on day 1 post-infection, respectively. Three healthy mice served as control. Tail vein blood samples were collected in two groups each with 10 mice during day 1-7 post-infection. The parasitemia was monitored daily by examining Giemsa-stained thin film. The survival rate of infected mice was calculated. Before infection, on day 3 and 5 post-infection, the spleen was aseptically removed from each mouse in infection group (n=3) and Treg blockade group (n=3), and splenocyte suspensions were prepared. The proportion of Treg and Th17 cells were analyzed by flow cytometry. The ratio of Treg/Th17 cells was calculated and the relative analysis of the percentage of Treg and Th17 cells was conducted.

Results: Parasitemia appeared on day 2 post-infection in infection group. On day 5, the infection rate of P. yoelii in erythrocytes increased to (49.8±4.7)% with a survival rate of 60.0%. All mice died on day 6 post-infection. In Treg blockade group, P. yoelii 17XL-parasitized erythrocytes appeared on day 2 post-infection; the parasitemia was (10.0±3.5)% on day 5, and increased rapidly to 60.0% on day 7; all mice died on day 8. The percentages of Treg and Th17 cells reached (11.1±1.3)% and (16.7±3.3)% respectively on day 3 post-infection in infection group, and increased to (26.1±4.5)% and (19.6±2.6)% on day 5, considerably higher than that of the control (P<0.01). The ratio of Treg/Th17 cells was 0.7±0.1, 1.3±0.4 on day 3 and 5 post-infection in infection group, respectively, which was much lower than that of normal control (2.1±0.5) (P<0.01, P<0.05). On day 3 and 5 post-infection, the percentages of Treg cells in CD4+ T cells was (2.4±1.3)% and (4.3±2.9)%, respectively, and that of Th17 cells reached (26.1±2.2)% and (6.5±2.1)% in Treg blockade group. The ratio of Treg/Th17 cells in Treg blockade group was 0.1±0.1 and 0.7±0.4, respectively, which was considerably lower than that of the control (3.6±0.4)(P<0.01). The proportion of Treg cells in CD4+ T cells was positively correlated with that of Th17 cells (r=0.8166, P<0.01).

Conclusion: The ratio of Treg/Th17 cells significantly decreases in the early stage of P. yoelii 17XL infection.