Figure 1. Expression of H1R in human gingival fibroblasts (HGF) and IL-8 secretion from the cells in response to histamine. (A) Total RNA was extracted from confluent gingival fibroblasts. THP-1 cells were used as a positive control. cDNA was prepared and analyzed for the mRNA expression of β-actin, H1R, and H2R by RT-PCR. M, molecular-weight marker. (B) Cell membrane fraction was separated from gingival fibroblasts and THP-1 cells and mixed with Laemmli sample buffer. Samples (equivalent to 106 cells each) were then subjected to Western blotting with rabbit anti-human H1R antibody. (C) Gingival fibroblasts and THP-1 cells were stained with 2 different rabbit anti-human H2R antibodies and analyzed by flow cytometry. Results in A, B, and C are representative of those from six donors with similar results. (D,E) Gingival fibroblasts were stimulated with the indicated concentrations of histamine for 24 hrs (D) or with 100 µmol/L of histamine for the time indicated (E). Supernatants were then 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 < 0.05, and **p < 0.01 compared with the unstimulated control (medium alone).