Adequacy of adsorption of post-immunization serum anti-NHba (Panel A) and anti-fHbp antibodies (Panel B) as measured by ELISA. The Y-axis shows the mean antibody concentrations and ranges of duplicate independent dilutions in arbitrary units (U) per ml (See methods). On some bars, the ranges are not evident because the differences between the respective replicate titers were small. Diagonal hatched bars, unadsorbed sera; open bars, sera adsorbed with irrelevant antigen (recombinant human albumin); black bars, adsorbed with NHba; gray bars, adsorbed with fHbp. The antibody concentrations in unadsorbed sera obtained before vaccination were <100 U/ml.