A recombinant macrophage infectivity potentiator (rMIP) protein of Neisseria meningitidis induces significant serum bactericidal antibody production in mice and is a candidate meningococcal vaccine antigen. However, bioinformatics analysis of MIP showed some amino acid sequence similarity to human FK506-binding proteins (FKBPs) in residues 166 to 252 located in the globular domain of the protein. To circumvent the potential concern over generating antibodies that could recognize human proteins, we immunized mice with recombinant truncated type I rMIP proteins that lacked the globular domain and the signal leader peptide (LP) signal sequence (amino acids 1 to 22) and contained the His purification tag at either the N or C terminus (C-term). The immunogenicity of truncated rMIP proteins was compared to that of full (i.e., full-length) rMIP proteins (containing the globular domain) with either an N-or C-terminal His tag and with or without the LP sequence. By comparing the functional murine antibody responses to these various constructs, we determined that C-term His truncated rMIP (؊LP) delivered in liposomes induced high levels of antibodies that bound to the surface of wild-type but not ⌬mip mutant meningococci and showed bactericidal activity against homologous type I MIP (median titers of 128 to 256) and heterologous type II and III (median titers of 256 to 512) strains, thereby providing at least 82% serogroup B strain coverage. In contrast, in constructs lacking the LP, placement of the His tag at the N terminus appeared to abrogate bactericidal activity. The strategy used in this study would obviate any potential concerns regarding the use of MIP antigens for inclusion in bacterial vaccines. N eisseria meningitidis (meningococcus) infections contribute significantly to mortality and morbidity worldwide (1). Implementation of capsular polysaccharide-protein conjugate vaccines against serogroups A, C, Y, and W into the routine immunization schedules of developed countries has been successful (2-5), but this approach cannot be used for serogroup B strains. The polysaccharide capsule of serogroup B meningococci (MenB) shows structural mimicry of human fetal brain neural cell adhesion molecules (6). Licensed MenB vaccines based on lipooligosaccharide (LOS)-depleted outer membrane (OM) vesicles (V) have been used to control serosubtype strain-specific clonal outbreaks of MenB infection, e.g., in Norway (7), Cuba (8), Brazil (9), and New Zealand (10), but they do not provide cross-strain protection (11). Recently, the 4CMenB (Bexsero) vaccine, developed using a genome-based reverse-vaccinology approach (12), has received a license from the European Union and has been recommended by the Joint Committee for Vaccination and Immunization for the routine vaccination of infants in the United Kingdom since 2014. The vaccine consists of the factor H binding protein (fHbp, fused to GNA2091 carrier protein), neisserial heparin binding protein (NHBA, fused to GNA1030 carrier protein), and an adhesin, NadA, mixed with the Men...