Threshold level of Riemerella anatipestifer crossing blood-brain barrier and expression profiles of immune-related proteins in blood and brain tissue from infected ducks

Riemerella anatipestifer (R. anatipestifer) is a Gram-negative bacterium that crosses the blood-brain barrier (BBB) and causes meningitis with neurological symptoms in infected ducks. A threshold level of bacteremia must be reached before the BBB can be breached. In this study, the bacterial burden and expression profiles of immune-related proteins in blood and brain tissue samples from R. anatipestifer-infected ducks were investigated. The data showed that R. anatipestifer could cross the BBB with low-level bacteremia of 7.5 × 102 CFU/ml in infected blood. Analysis of immune-related proteins revealed that IL-4, IL-17A, IL-17D, TLR3, TLR4, TLR7, and TGF-β in blood, as well as IL-1β, IL-2, IL-4, IL-17A, IL-17D, IL-17F, TLR3, TLR4, and TGF-β in brain tissue were upregulated at an early stage in infection. The expression levels of Th1 and Th17-specific cytokines were significantly higher than those of Th2-specific cytokines, which indicated that mainly Th1 and Th17 immune responses were induced during R. anatipestifer infection.