Involvement of VDR in synergistic effects of combined butyrate and active vitamin D3 on Salmonella-induced IL-6, IL-8, IL-1β, TNF-α, and hBD-2 mRNA expression in Caco-2 cells. Transfection of Caco-2 cells with control siRNA or VDR siRNA (si: siRNA to VDR) was carried out for 48 h. Transfected Caco-2 cells were infected by a constant concentration of S. typhimurium wild-type strain SL1344 (ST), in the presence of 1,25D3 (VD), butyrate (BU), or a combination of both (VD+BU); total RNA was extracted, reverse transcribed to cDNA, and RT-PCR analyses were performed to estimate amounts of IL-6 (a), IL-8 (b), TNF-α (c), IL-1β (d), and hBD-2 (e) transcript in Salmonella-infected cultured cells. Relative quantification based on internal reference gene (GAPDH transcript) to determine fold-differences in expression of the target genes, IL-6, IL-8, IL-1β, TNF-α, and hBD-2 mRNA were measured, and the fold increase over uninfected control cells (CON) is shown. Results are represented as mean ± SEM for at least three determinations from independent experiments. An asterisk indicates significant differences among groups, based on one-way ANOVA. *, p < 0.05, ** p < 0.01.