Role of NK Cells and Gamma Interferon in Transplacental Passage of Toxoplasma gondii in a Mouse Model of Primary Infection

Abstract

ABSTRACT Protective immunity in mice infected with Toxoplasma gondii is mainly mediated by NK cells, CD4 and CD8 T cells, and type 1 cytokines, such as gamma interferon (IFN-γ). To clarify the roles of NK cells and IFN-γ in protection against primary congenital toxoplasmosis, we used recombination activating gene 2 knockout (RAG-2 −/− ) mice, which lack T and B lymphocytes, in comparison with the wild-type BALB/c model. RAG-2 −/− mice had a significantly lower risk of fetal toxoplasmosis than BALB/c mice (25 versus 63.9%; P = 0.003). This protection was associated with an increased number of maternal NK cells, IFN-γ secretion by spleen cells, and decreased parasitemia. In the RAG-2 −/− mice, NK cell depletion increased both the rate of fetal infection, to 56.5% ( P = 0.02), and the blood parasite burden. Conversely, in the BALB/c mice, this treatment did not modify maternofetal transmission or the blood parasite burden. Neutralization of IFN-γ in both infected RAG-2 −/− and BALB/c mice decreased congenital Toxoplasma transmission, contrasting with an exacerbation of maternal infection. These data suggest that a partially protective immunity against congenital toxoplasmosis is achieved due to the increased number of NK cells in RAG-2 −/− mice. However, it seems that IFN-γ enhances, directly or indirectly, the transplacental transmission.