Pidotimod Inhibits Activation of Latent Toxoplasma gondii Infection Induced by Dexamethasone in Mice

Objective To study the inhibition effect of pidotimod(PT) on dexamethasone(Dem)-induced reactivated toxoplasmosis in mice. Methods A total of 96 female BALB/C mice were infected orally with 30 cysts of Toxoplasma gondii TgCtwh6 strain(genotype Chinese 1). 4 weeks later the mice were divided into three groups(A, B, and C). Mice of group A(Dem+NS) were given Dem [6 mg/(kg·d)] intraperitoneally and 200 μl normal saline given orally. Mice of group B(Dem+PT) were orally given pidotimod [100 mg/(kg·d)] and intraperitoneally injected with Dem [6 mg/(kg·d)] simultaneously.Each mouse in group C received 200 μl normal saline intraperitoneally. The mice were injected and given by gavage for 5weeks. After treatment, three mice in each group were scarified weekly, and the survival time of the mice was recorded in days. Brain parasite burden and T. gondii DNA copies in serum were detected by quantitative real-time PCR. T cell subsets, cytokine profiles in each group were analyzed by flow cytometry, and CBA kit, respectively. Results On the second week after Dem administration, parasitemia appeared in group A; in 5 weeks 50% mice had parasitemia again, and 17 mice died. Comparatively, in group B parasitemia appeared on the third week after PT and Dem administration, in 5 weeks 25% mice had parasitemia again, and 7 mice died. Parasitemia did not appear in Group C. On the 21st day after Dem administration, T. gondii DNA copies in brain tissues of group A was(209±12)×10 9, significantly higher than(62±10)×10 9 in group B treated with PT(n=3, P0.01). Flow cytometry test showed that on the 21st day after Dem administration, the proportions of Th1, Th2 and Treg cells in groups A and B were(4.0±1.5)% and(6.1±1.0)%,(0.6±0.1)% and(0.5±0.2)%, and(5.0±0.9)% and(7.0±1.2)%, respectively. There was siginificant difference in the percentages of Th1 and Treg between group B and A(P0.01). The levels of IFN-γ, TNF-α in group A were(2.2±0.7) pg/ml and(20.1±5.0) pg/ml, respectively, lower than that of group B [(3.6±0.6) pg/ml and(32.0±8.0) pg/ml](P0.01). No statistical significance was found in the levels of IL-4 and IL-10 between group A[(2.6±0.4) pg/ml,(39.0±6.0) pg/ml] and group B [(2.7±0.7) pg/ml,(40.0±8.0) pg/ml](P0.05). Conclusion Pidotimod can inhibit activation of latent Toxoplasma gondii infection induced by dexamethasone in mice. Th1 and Treg cells may contribute to the pidotimod/dexamethasone-induced immunoregulation.