FH and infection: Interestingly, the association constant of the fH-fHbp binding is 2.5-fold lower in case of fHbp of subfamily A (P = 0.04), indicating a slightly reduced on-rate of fH to fHbp of subfamily A. Together, these differences between fHbp of subfamily A and B prompt us to evaluate the relation between clinical course and infection with meningococci with either subfamily fHbp.