Serum absorption with purified P. gingivalis LPS. Four OMV-immunized serum samples (OMV-1, -2, -3, -4) and 1 mock-immunized serum sample were subjected to absorption assays. Before and after absorption for one to four times with LPS, 100 μl samples after dilution at 1:100 were pipetted into the wells of ELISA plates pre-coated with PMB and P. gingivalis LPS. P. gingivalis LPS-specific IgG was examined. The results are expressed as percent of absorbance at 405 nm after 15 min of incubation with alkaline phosphatase substrate as compared to the same samples without absorption. Absorbance ratios are shown as the mean ± SD from three independent experiments. Statistical analysis was performed using ANOVA followed by the Dunnett's multiple comparison test. Asterisks indicate that the ratio significantly was decreased.