Preventive And Therapeutic Effect Of Pidotimod On Reactivated Toxoplasmosis In Mice

Objective: Toxoplasma causes a subclinical infection in most immunocompetentindividuals, recrudescence of tissue cysts is an increasing problem in patients withimmunodeficiencies due to various causes, such as cancer chemotherapy, HIV/AIDS,organ transplant recipients, and immunosuppressive therapy for autoimmune diseases.In these processes, toxoplasmosis almost always happens as a result of reactivation oflatent infection. Previous data demonstrated that the synthetic dipeptide pidotimod(3-L-pyroglutamyl-L-thiaziolidine-4-carboxylic acid) is a potent immunostimulatingagent of improving the immunodefence in immunodepression in vitro and in vivo. Toinvestigate the efficacy of pidotimod as an oral preventative treatment, we used amurine model of reactivated toxoplasmosis in cyclophosphamide (CY)-inducedimmunosuppressed mice by administration of pidotimod. Possible immunoregulatorymechanisms were examined by studying the changes of parasitemia, the survival time、 CD4~+T helper cell subpopulations and associated cytokine expression.MeterialsBALB/c mice were orally infected with200μl of brain homogenate containing20parasite cysts. The mice were divided into three groups with thirty mice in each.Cyclophosphamide (CY) was given intraperitoneally every second day to induce theimmunosuppression, except for the control group which received normal saline (NS).Mice of the control group (Group CY+NS) were given CY intraperitoneally and NSorally; mice in the preventive treatment group were orally given pidotimod and injectedintraperitoneally with CY. Animals were sacrificed under anesthesia using ether aftervarious intervals days of CY administration. For parasitemia determination,200μl ofblood was processed following strict decontamination procedures. The amplificationswere carried out with TOX-Fluorescence Quantitative PCR kit. Fresh single-cellsuspensions of leukocytes from spleen were prepared, analyses of CD4+T cellsubpopulations by flow cytometry, quantification of transcription factors mRNA byquantitative real-time PCR, the cytokine production was measured in serum samplesfrom each animal using the CBA mouse Cytokines Kit, the histopathology of brains andparasite burden in the brain using the TOX-Fluorescence Quantitative PCR.ResultsPidotimod treatment significantly decreased the parasite load in the blood andincreased the survival of CY-induced immunocompromised mice. The inflammatorybrain lesions and parasite burden in the brain of CY-induced reactivated toxoplasmosishad been significantly ameliorated by PT treatment. The percentage of the Th1, ratherthan the Th2and Th17cells, was restored in PT-treated CY-induced mice. Interestingly,an increase of Treg cells was also observed simultaneously in this group.Conclusions：The present work showed that immunostimulating agent pidotimod pre-treatmenthas a significant effect on the alleviation of parasitemia, prolonging survival time and the brain inflammatory lesions in mice with reactivated toxoplasmosis throughenhancing Th1mediated cellular immunity.