Outer Membrane Proteins BB0405 and BB0406 Are Immunogenic, but Only BB0405 Is Required for Borrelia burgdorferi Infection

Abstract

We recently identified the Borrelia burgdorferi outer membrane protein (OMP) BB0406 and found that the gene encoding this OMP was cotranscribed with the gene encoding the OMP BB0405. Interestingly, BB0405 and BB0406 share 59% similarity and are grouped into the same B. burgdorferi paralogous gene family. Given their overall similarity, it is plausible that both OMPs have similar or overlapping functions in this pathogenic spirochete. BB0405 was recently shown to be required for mammalian infection despite the observations that BB0405 is poorly immunogenic and not recognized during mouse or human infection. BB0405 orthologs have also been shown to bind the complement regulator protein factor H. Therefore, to better elucidate the role of BB0405 and its paralog BB0406 during infection and in serum resistance, we examined both proteins in animal infection, factor H binding, and serum sensitivity assays. Our combined results suggest that BB0405-and BB0406-specific antibodies are borreliacidal and that both OMPs are immunogenic during nonhuman primate infection. Additionally, while BB0405 was found to be required for establishing mouse infection, BB0406 was not found to be essential for infectivity. In contrast to data from previous reports, however, neither OMP was found to bind human factor H or to be required for enhancing serum resistance of B. burgdorferi in vitro.KEYWORDS Borrelia burgdorferi, Lyme disease, outer membrane proteins, spirochete L yme disease is a multisystem infection caused by pathogenic spirochetes belonging to the Borrelia burgdorferi sensu lato complex (1, 2). It is the most prevalent arthropod-borne disease in the United States and has become a major public health concern (3, 4). The enzootic life cycle of the spirochete is complex and involves tick vectors of the Ixodes genus that transmit the spirochete to a wide range of mammalian host reservoirs in nature. Humans are accidental hosts and play no significant role in the spirochete life cycle (5). The primary manifestations of Lyme disease are a localized rash, termed erythema migrans, and flu-like symptoms (6). In the absence of antibiotic treatment, spirochetes can disseminate to multiple organs, including the heart, joints, skin, and nervous system (7). To disseminate to these distant sites, the spirochete must evade serum-mediated killing and the subsequent adaptive immune response that ensues in the mammalian host (5,6,8).Given that B. burgdorferi is an extracellular pathogen, the outer membrane (OM) of this organism is the interface between the spirochete and the host during infection. The two major classes of proteins present in the borrelial OM are (i) outer surface lipoproteins (Osps) that are anchored to the outer leaflet of the OM bilayer by their N-terminal lipid moieties and (ii) integral outer membrane proteins (OMPs) that contain membrane-spanning domains. Membrane-anchored Osps have been well studied be-

Identification of Surface Epitopes Associated with Protection against Highly Immune-Evasive VlsE-Expressing Lyme Disease Spirochetes

“…Likewise, during human infection, anti-BB0405 antibodies are not detected either. Interestingly, even though anti-BB0405 polyclonal antibodies are borreliacidal in vitro (52,54), immunization of mice with recombinant BB0405 does not affect any spirochetal burden in infected mice. However, this immunization still induces a long-lasting antibody response, as demonstrated by WB analysis and enzyme-linked immunosorbent assay (ELISA) (53).…”

“…Also, it has been previously suggested that, during mammalian infection, BB0405 is camouflaged by "abundant neighboring outer membrane proteins" (53). Accordingly, VlsE molecules may well fill the role of these neighboring outer membrane proteins and may explain why anti-BB0405 antibodies are borreliacidal only to in vitro-grown spirochetes (52,54), whose VlsE expression is very low (25).…”

“…Peptides p40, p60, and p168 represent three putative linear epitopes of outer membrane protein BB0405. BB0405 is shown to be poorly immunogenic in the mammalian host during an early stage of infection (52,53). In mice, anti-BB0405 antibodies do not develop for at least 1 month after B. burgdorferi infection (53).…”

“…Antibodies generated against B. burgdorferi B31 recognize orthologs of different infectious Borrelia strains (53). Importantly, BB0405 is absolutely required for mammalian infection (52,53). Thus, BB0405 is a strong vaccine candidate whose newly identified putative epitopes should be tested as potential targets of an LD subunit vaccine.…”

Delineating Surface Epitopes of Lyme Disease Pathogen Targeted by Highly Protective Antibodies of New Zealand White Rabbits

“…A downstream application of computational algorithms resulted in mapping of PA epitopes on several surface proteins of B. burgdorferi. Importantly, whenever prior data were available (69,(82)(83)(84)(85)(86)(87)(88), the mapped surface proteins were shown to be immunogenic, capable of inducing protection against wild-type challenge, and critical for B. burgdorferi pathogenesis or growth, all of which are desired characteristics of a strong vaccine candidate (59). Similarly, whenever available, published studies empirically proved the surface exposure of the PA epitope-containing domains of these proteins (59).…”