Outer surface protein C (OspC) is a differentially expressed major surface lipoprotein of Borrelia burgdorferi. ospC is swiftly upregulated when spirochetes leave the Ixodes scapularis tick gut, migrate to the salivary gland, and exit the arthropod vector. Here we show that OspC strongly binds to the tick salivary gland, suggesting a role for OspC in spirochete adherence to this tissue. In vivo studies using a murine model of Lyme borreliosis showed that while OspC F(ab) 2 fragments did not influence either the viability of spirochetes or ospC gene expression, they did interfere with B. burgdorferi invasion of tick salivary glands. We then generated ospC knockout spirochetes in an infectious clone of B. burgdorferi and examined them within the vector. OspC-deficient or wild-type spirochetes persisted equally within the gut of unfed ticks and multiplied during the tick engorgement; however, unlike wild-type B. burgdorferi, the mutants were unable to invade salivary glands. Salivary gland colonization of OspC-deficient spirochetes was completely restored when this mutant was complemented in trans with a plasmid harboring the wild-type ospC gene. These studies conclusively demonstrate the importance of OspC in the invasion of tick salivary glands by B. burgdorferi, a critical step in the transmission of spirochetes from the arthropod vector to the mammalian host.

Outer surface protein C (OspC) is a differentially expressed major surface lipoprotein of Borrelia burgdorferi. ospC is swiftly upregulated when spirochetes leave the Ixodes scapularis tick gut, migrate to the salivary gland, and exit the arthropod vector. Here we show that OspC strongly binds to the tick salivary gland, suggesting a role for OspC in spirochete adherence to this tissue. In vivo studies using a murine model of Lyme borreliosis showed that while OspC F(ab) 2 fragments did not influence either the viability of spirochetes or ospC gene expression, they did interfere with B. burgdorferi invasion of tick salivary glands. We then generated ospC knockout spirochetes in an infectious clone of B. burgdorferi and examined them within the vector. OspC-deficient or wild-type spirochetes persisted equally within the gut of unfed ticks and multiplied during the tick engorgement; however, unlike wild-type B. burgdorferi, the mutants were unable to invade salivary glands. Salivary gland colonization of OspC-deficient spirochetes was completely restored when this mutant was complemented in trans with a plasmid harboring the wild-type ospC gene. These studies conclusively demonstrate the importance of OspC in the invasion of tick salivary glands by B. burgdorferi, a critical step in the transmission of spirochetes from the arthropod vector to the mammalian host.

Sera from selected patients with Lyme disease in different stages were used to passively immunize mice against Borrelia burgdorferi challenge to determine if human antibodies could protect the animals from infection. Sera from 2 patients with late-stage Lyme disease that contained strong antibody reactivity to proteins in B. burgdorferi lysates, including antibodies to the outer surface proteins (Osps) A and B, partly protected mice from infection after challenge with a small inoculum (10(2)) of B. burgdorferi. Mice immunized with sera from either of these 2 patients developed significantly fewer infections from the borreliae (patient 1 serum, 5%; patient 2 serum, 25%) relative to control mice (patient 1 serum, 90%; patient 2 serum, 74%). In contrast, sera from 2 patients with early or late Lyme disease that lacked antibodies reactive to OspA and OspB did not confer protection. Immunity appeared to be related, at least in part, to the presence of a strong humoral response to the Osps. These results suggest that during prolonged infection, some patients develop an immune response that may be partly protective against reinfection with B. burgdorferi. Therefore, although most patients do not mount a strong humoral response to the Osps during natural infection, vaccination with an Osp may elicit protective immunity.

SummaryThe expression of a Borrelia burgdorferi gene, erpT, was investigated throughout the spirochaete life cycle in the arthropod vector and the murine host. Three phage clones from a B. burgdorferi DNA expression library synthesized a 30 kDa antigen that was recognized by antibodies in the sera of B. burgdorferiinfected mice but not mice hyperimmunized with B. burgdorferi lysates. Differential antibody binding suggested that this protein was preferentially expressed in vivo. This antigen was designated ErpT, based upon 99.6% homology with the BBF01 sequence in the B. burgdorferi genome. ErpT was not detected on spirochaetes cultured in BSK II medium by indirect immunofluorescence or in B. burgdorferi lysates by immunoblotting, implying that ErpT is not readily produced in vitro. erpT mRNA was not discernible by Northern blot but was identified by RNA polymerase chain reaction in vitro, indicating that erpT is expressed at low levels by cultured spirochaetes. erpT expression was then investigated in the vector and mice because B. burgdorferi do not normally reside in culture medium. RNA polymerase chain reaction and immunofluorescence studies demonstrated that erpT was expressed by a small minority of B. burgdorferi (11/500, 2.2%) within unfed ticks and then repressed during engorgement. erpT mRNA or ErpT antibodies were first detected in B. burgdorferi-infected mice at 4 weeks, suggesting that erpT was not expressed in the early stages of murine infection. Then, during persistent infection, RNA polymerase chain reaction showed that erpT was expressed by B. burgdorferi within the joints, heart and spleen, but not by spirochaetes in the skin. Immunization of mice with ErpT was antigenic but was not protective. These studies demonstrate that B. burgdorferi erpT is differentially expressed throughout the B. burgdorferi life cycle, in both the vector and the mammalian host, and is primarily expressed in extracutaneous sites during murine infection.

Borrelia burgdorferi outer surface protein OspB is expressed by spirochetes in the Ixodes scapularis gut. ospB is transcribed from a bicistronic operon with ospA, a known spirochete adhesion gene in the tick gut. Here we examine whether OspB also has a specific function in ticks. OspB specifically binds to a protein or protein complex within the tick gut. We also assessed whether selected nonborreliacidal OspB antibodies or F(ab) 2 fragments interfere with B. burgdorferi-tick attachment in vivo. We examined engorged ticks that fed on B. burgdorferi N40-infected scid mice that had been treated with OspB F(ab) 2 fragments. Control F(ab) 2 fragments did not interfere with B. burgdorferi colonization of the tick gut, whereas OspB F(ab) 2 fragments significantly inhibited the attachment of spirochetes to the tick gut. These studies show that nonbactericidal OspB antibodies interfere with B. burgdorferi colonization of I. scapularis, highlighting a specific role for OspB in spirochetearthropod interactions and suggesting new antibody-mediated strategies for interfering with B. burgdorferi transmission.

SummaryDiversity and mutations in the genes for outer surface proteins (Osps) A and B ofBorrelia burgdorferi sensu lato (13, burgdorferi), the spirochetal agent of Lyme disease, suggests that a monovalent OspA or OspB vaccine may not provide protection against antigenically variable naturally occurring B, burgdorferi. We now show that OspA or OspB immunizations protect mice from tick-borne infection with heterogeneous/g burgdorferi from different geographic regions. This result is in distinct contrast to in vitro killing analyses and in vivo protection studies using syringe injections of/g burgdorferi as the challenge inoculum. Evaluations of vaccine efficacy against Lyme disease and other vector-borne infections should use the natural mode of transmission and not be predicated on classification systems or assays that do not rely upon the vector to transmit infection.V accination with outer surface proteins (Osps)lA or B from a Borrelia burgdorferi sensu law (13, burgdorferi) isolate (designated N40) protected C3H/HeJ mice from infection when challenged with the same strain (1, 2). Humoral immunity was sufficient for protection as the passive transfer of OspA or OspB antibodies protected C.B.-17 scid or C3H mice from/3; burgdorferi infection (1-4). OspA and OspB variability, including amino acid differences or truncations of the COOH terminus of the Osps, however, allowed/~ burgdorferi to survive in the presence of protective antibody in vitro and in vivo, predicting a lack of vaccine efficacy (2, 5-11). In addition, spirochetes have been identified that lack the 49-kb plasmid encoding ospA and ospB or have chimeric Osps due to homologous recombination between ospA and ospB, suggesting that OspA or OspB mediated immunity would not be protective in the event of infection by these mutants (7,12). The infectivity of these mutant spirochetes in selected hosts has not yet been delineated. RFLP, multilocus enzyme electrophoresis, or nucleic acid hybridization studies distinguished as many as four groups of/t burgdorferi, with the 1 Abbreviation used in this paper: Osp, outer surface protein. 215description of three new proposed species-/g burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii (13)(14)(15)(16)(17). Similarly, reactivity with OspA mAbs divided/g burgdorferi into seven serogroups which upon detailed analysis (several of the serotypes were variants of the three species that arose from osp recombination) corresponded to the three new species (13). lg burgdo~feri sensu stricto is prevalent in North America whereasEuropean sites may contain all three species. In vivo passive immunization studies demonstrated that antiserum against spirochetes from individual groups protected scid mice or hamsters against challenge with homologous, but not heterologous/~ burgdorferi (8,18).The in vivo protection studies used single isolates of/~ burgdorferi, and syringe inoculations as the method of spirochete challenge, and therefore do not mimic natural transmission of the agent. Accordingly, we have shown that v...

Environmental insults such as microbial pathogens can contribute to the activation of autoreactive T cells, leading to inflammation of target organs and, ultimately, autoimmune disease. Various infections have been linked to multiple sclerosis and its animal counterpart, autoimmune encephalomyelitis. The molecular process by which innate immunity triggers autoreactivity is not currently understood. By using a mouse model of multiple sclerosis, we found that the genetic loss of the MAPK, c-Jun N-terminal kinase 1 (JNK1), enhances IL-10 production, rendering innate myeloid cells unresponsive to certain microbes and less capable of generating IL-17-producing, encephalitogenic T cells. Moreover, JNK1-deficient central nervous system myeloid cells are unable to respond to effector T cell inflammatory cytokines, preventing further progression to neuroinflammation. Thus, we have identified the JNK1 signal transduction pathway in myeloid cells to be a critical component of a regulatory circuit mediating inflammatory responses in autoimmune disease. Our findings provide further insights into the pivotal MAPK-regulated network of innate and adaptive cytokines in the progression to autoimmunity.c-Jun N-terminal kinase ͉ experimental autoimmune encephelomyelitis ͉ innate immunity ͉ macrophages

Antibodies in sera of 7 patients with neurologic manifestations of Lyme borreliosis and a monoclonal antibody (mAb H9724) to the flagellin of Borrelia burgdorferi have been shown to bind neural tissue. To identify the antibody binding site common to the B. burgdorferi flagellin and the neural tissue, we made recombinant fusion proteins expressing epitopes of flagellin. Antibodies in patients' sera and mAb H9724 bound within an 18-amino acid epitope (residues 208-225) in the central region of flagellin, whereas two other mAbs bound to epitopes mapping elsewhere in the protein. Antibodies in patients sera and mAb H9724 also bound to a human neuroblastoma cell line. Absorption of patients sera with a peptide, EGVQQEGAQQPA, corresponding to amino acids 213-224 of flagellin, inhibited binding to the neuroblastoma cell line. The data suggest that the immune response to a specific B-cell epitope within flagellin, shared by a human neuroblastoma cell line, may be involved in the pathogenesis of neuroborreliosis.