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-The present work compared inbred (CBA/Ca) and outbred (Swiss white) strains of mice for their capacity to cope with a Neospora caninum infection and to consistently produce tissue cysts. In each experiment Swiss white and CBA/Ca mice were given three different doses of NC-1 tachyzoites. Lymphoproliferative and humoral responses as well as cytokine production were evaluated eight weeks after infection (PI) whereas tissue cyst production and histopathology were assessed 4, 6 and 10 weeks PI in immunosuppressed mice. Tissue cysts were observed 10 weeks after infection only in CBA/Ca mice receiving the two highest inoculum doses. Furthermore this strain showed the highest specific lymphoproliferative response. A mixed cytokine response with elevated IFN-γ and fairly low IL-4 and IL-10 secretion was recorded. In both strains, no lesions were observed in the tissues of infected mice. This study indicates that CBA/Ca female mice infected with 5 × 10 6 NC-1 tachyzoites represent a useful model for the study of specific maternal immune responses in pregnant animals.Neospora caninum / immune response / resistance / cyst / mice

The factors responsible for the reactivation of a Neospora caninum latent infection are unknown, but it is postulated that the maternal immune response could be altered during pregnancy. The immune response was investigated in N. caninum chronically infected mice during successive pregnancies as well as in non-pregnant infected mice and mice infected when pregnant. Vertical transmission was demonstrated in chronically infected mice after the first pregnancy but the rate of foetal infection fell after further pregnancies. Non-pregnant chronically infected mice showed a marked specific proliferative response and an IgG2a isotype preferential secretion. During the course of the first pregnancy, no significant modification of the immune response was recorded. After 2 successive pregnancies, the specific cellular response showed a significant fall whereas Th2 cytokine mRNA expression was noted. At the same time, IgG1 secretion increased to reach the IgG2a level. At the third delivery, a partial restoration of the proliferative response was observed. The reactivation of N. caninum chronic infection during pregnancy does not seem to be consecutive to an immunodepression. Nevertheless, pregnancy could favour parasite multiplication in utero after an occasional spontaneous release of bradyzoites.

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