IL6 and infection: The expression levels of interleukin 1 beta (IL-1β), IL-6, IL-8, IL-10, IL-17A, and the interleukin receptor IL-17RA were significantly increased after infection with Yb2 and cYb2ΔsspA and were much greater than those in the brains of control and Yb2ΔsspA-infected ducks at 24 and 48 hpi (Figure 4).