ICAM-1 mediates invasion of P. gingivalis. (A) Ca9-22 cells were incubated with P. gingivalis for 1 h. The cells were then stained using anti-ICAM-1 antibody. ICAM-1 is shown in green and P. gingivalis is shown in red. Bars in each panel are 10 μm. (B) TNF-α increased expression of ICAM-1 in Ca9-22 cells. Ca9-22 cells were treated with 10 ng/ml of TNF-α for 3 h. The cells were lysed and the expression of ICAM-1 and Rab5 was analyzed by Western blotting with antibodies for each molecule. (C) Antibody to ICAM-1 inhibits invasion of P. gingivalis in cells. Ca9-22 cells were treated with TNF-α for 3 h and were then incubated with an anti-ICAM-1 antibody or a control IgG antibody for 2 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 (+).