F4 fimbriae trigger mRNA expression of IL-17 cytokines in PBMCs upon oral immunization. The piglets were immunized with 1 mg F4 fimbriae on day 0 (D0), D1 and D2. PBMCs were isolated from piglets on D0 before immunization and on D4 and D9 after immunization. The mRNA expression in PBMCs isolated from F4-immunized or control piglets was analyzed by qPCR. The mRNA expression level was normalized to the reference genes and then to the control group for every separate day. Data are presented as the mean ± SEM (n = 5 per group). * p < 0.05, ** p < 0.01.