Figure 3. Involvement of functional H1R in the synergistic effects. Gingival fibroblasts were incubated in medium (A) or with TNF- (1 ng/mL) (B) in the presence or absence of histamine, the H1R agonist 2-pyridylethylamine, or the H2R agonist dimaprit at the indicated concentrations for 8 hrs. After incubation, the supernatants were collected, and the concentrations of IL-8 in the supernatants were determined by ELISA. The results are expressed as the mean ± SD for triplicate cultures. *p < 0.01 compared with medium or TNF- alone.