Fig. 7: Anti-capsular antibodies strengthen each other’s binding.

K. pneumoniae KpnO2 was incubated with 1 µg/ml directly labeled UKpn3-AF647 (anti-capsule) in the presence of a concentration range of (a) IgG1 antibodies (UKpn1, UKpn2, UKpn3 or UKpn6) or (b) different variants of UKpn1 (IgG1, F(ab’)2 or F(ab)) for 30 min at 4 °C. c K. pneumoniae KpnO2 was incubated with 1 µg/ml UKpn3-AF647 F(ab’)2 in the presence of a concentration range of different UKpn1 variants (IgG1, F(ab’)2 or F(ab)) for 30 min at 4 °C. a–c Antibody binding was detected by flow cytometry. The relative antibody binding was calculated by dividing the gMFI of the fluorescent antibody in presence of unlabeled antibody variants with the gMFI of the fluorescent antibody only. d K. pneumoniae KpnO2 was incubated with combinations of UKpn1 and UKpn3 variants for 30 min at 4 °C, followed by washing and addition of 3% NHS as complement source for 30 min at 37 °C. C3b deposition was measured using anti-hu-C3b-A647 by flow cytometry. a–d Data represent mean ± SD of three independent experiments.