A) P. gingivalis strain W83 was incubated with 50 µg/ml C4BP-FITC in the presence of several competitors: plasma purified C4BP (20 µg/ml), recombinant C4BP (20 µg/ml), C4b (100 µg/ml), mAb 104 (100 µg/ml), mAb 67 (100 µg/ml), heparin (100 µg/ml) and BSA (100 µg/ml). After 1h incubation at RT, the bacteria were washed and analyzed by flow cytometry. B) Recombinant C4BP and its mutants lacking single CCP domains were incubated with HRgpA and the binding was detected with a polyclonal antibody. Binding at every condition was analyzed three times in duplicates. Shown are mean values +/− SD. Statistical significance of differences between experimental conditions without (set as 1) and with competitors was estimated with Student’s t test, *p<0.05, ** p<0.01, *** p<0.001.