Anti–factor H–binding protein (fHBP) monoclonal antibody (MAb) reactivity with representative Neisseria meningitidis group B strains. Heat-killed, whole meningococci were applied to a membrane, which was probed with polyclonal antibody or MAb. Wild-type (WT) and fHBP knockout (KO) mutant strains from each variant group were tested. α-fHBP variant (v.) 1,2,3, mouse antisera raised against the individual fHBP v.1, v.2, and v.3 proteins and pooled; JAR 1, 3, and 5, MAbs raised against recombinant fHBP v.1; JAR 10, 11, 13, MAbs raised against recombinant fHBP v.2.