A, Inhibition of binding human fH to fHbp by immune sera as measured by ELISA. Dilutions of individual sera from transgenic mice (N=11 per vaccine group) immunized with wild-type (circular symbols) or R41S mutant (triangular symbols) fHbp vaccines were tested for their ability to inhibit binding of fH present in 5% IgG-depleted human serum (used as a source of human fH) to immobilized wild-type fHbp. At 1:100 and 1:400 dilutions, there was significantly greater inhibitory activity in the R41S mutant fHbp vaccine group (open triangles) than mice given the fHbp vaccine that bound fH (open circles, P<0.03). Filled diamonds represent inhibition of serum pools from transgenic mice immunized with aluminum adjuvant alone (N=4 pools). B, Correlation between fH inhibition and serum bactericidal activity of individual sera. Data are from sera of individual transgenic mice immunized with wild-type or R41S mutant fHbp vaccines (r = +0.69, P=0.0004).