Experimental reinfection of BALB/c mice with different recombinant type I/III strains of Toxoplasma gondii: involvement of IFN-gamma and IL-10.

To assess reinfection of BALB/c mice with different Toxoplasma gondii strains, the animals were prime infected with the non-virulent D8 strain and challenged with virulent recombinant strains. Thirty days after challenge, brain cysts were obtained from surviving BALB/c mice and inoculated in Swiss mice to obtain tachyzoites for DNA extraction and PCR-RFLP analysis to distinguish the different T. gondii strains present in possible co-infections. Anti-Toxoplasma immune responses were evaluated in D8-primed BALB/c mice by detecting IFN-gamma and IL-10 produced by T cells and measuring immunoglobulin levels in serum samples. PCR-RFLP demonstrated that BALB/c mice were reinfected with the EGS strain at 45 days post prime infection (dpi) and with the EGS and CH3 strains at 180 dpi. High levels of IFN-gamma were detected after D8 infection, with no significant difference between 45 and 180-day intervals. However, higher IL-10 levels and higher plasmatic IgG1 and IgA were detected from samples obtained 180 days after infection. BALB/c mice were susceptible to reinfection with different recombinant T. gondii strains and this susceptibility correlated with enhancement of IL-10 production.

Genetic variability of Brazilian Toxoplasma gondii strains detected by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) and simple sequence repeat anchored-PCR (SSR-PCR).

The genetic variability of 19 Toxoplasma gondii strains isolated from humans and animals in Brazil was detected by both random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) and simple sequence repeat anchored-PCR (SSR-PCR) for the first time. Two reference strains, RH (highly virulent) and ME49 (avirulent), were submitted to both assays. Besnoitia sp., Plasmodium falciparum and Babesia bigemina were used as outgroups. RAPD-PCR and SSR-PCR profiles were used for building phenetic trees by unweighted pair group method with arithmetic averages (UPGMA). Phenograms built with TREECONW software showed great similarity in the topology of the trees. Both phenograms presented two major clusters that grouped T. gondii strains according to their murine virulence. The strains AS28, BV and N, which are highly virulent for BALB/c mice, were clustered with the reference strain RH, the highly virulent strain of T. gondii that has been most commonly studied. The group formed by the cystogenic strains showed that the strains which presented a level of virulence more similar to that of ME49 strain (avirulent) also presented a closer genetic relationship. Genetic variation within each lineage was significantly lower (P < 0.05) than that between the lineages. Regarding outgroups, Besnoitia sp. presented the closest relationship to T. gondii while P. falciparum was the most distant. The results presented here demonstrate that intraspecific genetic variability separates Brazilian T. gondii strains into two groups which correlate with murine virulence phenotype.

Experimental reinfection of BALB/c mice with different recombinant type I/III strains of Toxoplasma gondii: involvement of IFN-³ and IL-10

To assess reinfection of BALB/c mice with different Toxoplasma gondii strains, the animals were prime infected with the non-virulent D8 strain and challenged with virulent recombinant strains. Thirty days after challenge, brain cysts were obtained from surviving BALB/c mice and inoculated in Swiss mice to obtain tachyzoites for DNA extraction and PCR-RFLP analysis to distinguish the different T. gondii strains present in possible co-infections. Anti-Toxoplasma immune responses were evaluated in D8-primed BALB/c mice by detecting IFN-³ and IL-10 produced by T cells and measuring immunoglobulin levels in serum samples. PCR-RFLP demonstrated that BALB/c mice were reinfected with the EGS strain at 45 days post prime infection (dpi) and with the EGS and CH3 strains at 180 dpi. High levels of IFN-³ were detected after D8 infection, with no significant difference between 45 and 180-day intervals. However, higher IL-10 levels and higher plasmatic IgG1 and IgA were detected from samples obtained 180 days after infection. BALB/c mice were susceptible to reinfection with different recombinant T. gondii strains and this susceptibility correlated with enhancement of IL-10 production.