F4 fimbriae elicit an IL-17 dominated cytokine response in naïve PBMCs. PBMCs were isolated from naïve piglets and were stimulated with F4 fimbriae (5 μg/mL) for 24, 48 and 72 h. The mRNA expression profile was analyzed by qPCR. mRNA expression levels were normalized to the reference genes and then to the control group for each time point. Then, the data for every day was plotted relative to day 0. Data are presented as the mean ± SEM (n = 3). NS: non-stimulated. * p < 0.05, ** p < 0.01.