Immune responses in pregnant cattle and bovine fetuses following experimental infection with Neospora caninum

Humoral and cell-mediated immune (CMI) responses [i.e. proliferative respon ses and gamma interferon (IFN-gamma) production], were elicited in five cow s infected between 159 and 169 days of gestation by a combined intravenous- intramuscular inoculation of Neospora caninum tachyzoites. Analysis of anti gen-specific immunoglobulin (IgG) subclasses revealed a predominant IgG2 re sponse in two cows, a mixed IgG1-IgG2 response in two other cows and a pred ominant IgG1 response in one cow. No correlation was found between IgG2 tit ers and IFN-gamma levels. CD4(+)T cells were responsible for the CMI respon ses in peripheral blood mononuclear cells from three infected cows. All fiv e fetuses removed from infected dams at week 9 post-infection (219-231 days of gestation) mounted strong Neospora-specific humoral responses and had a predominant IgG1 response, regardless of their ability to produce IFN-gamm a. However, CMI responses were highly variable between fetuses. These data indicate the complexity of the immune mechanisms associated with Neospora i nfection in both the dams and their fetuses.