TNF-α-augmented invasion of P. gingivalis is mediated by TNF receptor-I. (A) Expression of TNF receptors on Ca9-22 cells. Expression of TNF receptors in lysates of the cells was analyzed by Western blotting with anti-TNFR-I and anti-TNFR-II monoclonal antibodies. Human monocytic THP-1 cells were used as a positive control of TNFR-II. (B) Anti-TNFR-I antibody blocked TNF-a-augmented invasion of P. gingivalis in Ca9-22 cells. Ca9-22 cells were preincubated with 5 μg/ml of anti-TNFR-I monoclonal antibody or mouse IgG at 37°C for 1 h and were then incubated with TNF-α for 3 h. The cells were further incubated with P. gingivalis (MOI =100) for 1 h. Viable P. gingivalis in the cells was determined as described in Methods. (Means ± standard deviations [SD] [n = 3]). ††, P < 0.01 versus control + TNF-α (-); **, P < 0.01 versus none + TNF-α (+).