Figure 1. Selected mAbs against BP-2a 515 variant recognize only the polymerized pilus structures of the homologous strain and can mediate complement-dependent bacterial clearance.

(A) Flow cytometry analysis on whole GBS strains stained with mAbs raised against BP-2a 515 variant. Six GBS strains expressing different BP-2a variants were used in the assay, strain CJB111 (cjb111 allele); strain H36B (h36b allele); strain CDC84 (dk21 allele); strain CDC89 (cjb110 allele); strain 3050 (2603 allele) and strain 515 (515 allele). Fixed bacteria were stained with monoclonal antibodies and then labeled with R-Phycoerythrin conjugated goat anti-mouse secondary antibodies. Black filled histograms indicate staining of bacteria with only secondary antibody. (B) Opsonophagocytosis activity of the selected six monoclonal antibodies. 10⁴ CFUs of GBS strain 515 were incubated for 1 h with differentiated HL60 cells, baby rabbit complement and monoclonal antibody (1∶30, 1∶90, and 1∶270 dilutions). The log₁₀ differences between GBS colony-forming units at time 0 (10⁴ CFU) and time 1 h are shown. The mAbs used are recorded above each bar. Black shaded bars represent negative control (without baby rabbit complement); grey bars correspond to the polyclonal serum specific for the full length BP-2a 515 protein, used as positive control. Error bars indicate standard deviation from two independent experiments.