One of the reasons can be that in goats the C. burnetii infection is localised specifically in the placenta, and therefore no persistent systemic mRNA up-regulation was observed in the PBMCs from infected goats. Ben Amara et al. indeed found that C. burnetii replicates in vitro in placental derived trophoblasts and induces an up-regulation of cytokine mRNA. Therefore, they assumed that the specific inflammatory environment in the placenta, skewed MK-1775 towards tolerance and anti-inflammatory responses. This specific compartmentalized infection is also observed in chronic Q fever patients, as in these persons C. burnetii is mainly localised in the heart valve and vessels. At day 56 of our study TNF-a mRNA expression was increased in all goats compared to the initial level, but a significantly higher TNF-a mRNA expression was seen in the infected goats. This suggests that, besides the influence of the pregnancy, infection with C. burnetii also increases expression of TNF-a mRNA. We also showed a clear increase in IL-1b and IFN-c mRNA expression in the C. burnetii NM stimulated PBMCs derived from infected goats from day zero till day 56 of the study. However, at day 56, only IFN-c mRNA expression was significantly higher in the PBMCs from infected goats. The fold induction of naive and infected goats at day 56 was respectively 1.96 and 24.21, indicating the large effect on IFN-c mRNA expression of C. burnetii stimulated PBMCs from infected goats. The fold induction at day 56 in C. burnetii stimulated PBMCs from naive and goats was respectively 1.96 and 24.21. Besides the observed mRNA up-regulation, IFN-c protein levels were increased in C. burnetii stimulated PBMCs and whole blood from infected goats compared to naive goats. Thus although no systemic response in goats could be observed, PBMCs of C. burnetii infected goats respond differentially to C. burnetii stimulation compared to PBMC of uninfected goats. Stimulation with E. coli LPS did not lead to increased up-regulation of IFN-c mRNA expression in the C. burnetii infected goats, which demonstrates that the observed IFN-c response is specific for C. burnetii. Even though we hypothesized that C. burnetii infected PBMCs are translocated to the placenta, we assume that remaining memory T-cells in the peripheral blood can be activated and play a role in this immune response and increased IFN-c mRNA expression. The importance of TNF-a and IFN-c during C. burnetii infection has been shown by Andoh et al. These authors demonstrated that IFN-c2/2 and TNF-a2/2 mice have respectively high and modest susceptibility to C. burnetii NM infection and that the disease progressed rapidly in these mice. In humans, much research has been performed on the cytokine expression in chronic Q fever patients, a condition that in our opinion mostly resembles the C. burnetii re-stimulation of PBMCs from infected goats. TNF-a mRNA and TNF-a protein levels are increased in C. burnetii re-stimulated monocytes of chronic Q fever patients compared to healthy controls. Similarly, blood cells of chronic Q fever patients respond to C. burnetii stimulation with higher IFN-c production. The observed up-regulation of IFN-c mRNA expression after C. burnetii NM stimulation was also found for the inoculum strain C. burnetii 3262 and the other C. burnetii strains which indicates that the different C. burnetii strains contain corresponding antigens on their surfaces which are recognized by goat PBMCs. Similar cross reactivity was demonstrated by Arricau-Bouvery et al. in a vaccination study in goats. Based on these results we decided to perform our stimulation experiments with C. burnetii Nine Mile.