R. Mark Wooten

Toll-like receptor 2 is required for innate, but not acquired, host defense to Borrelia burgdorferi

Borrelia burgdorferi lipoproteins activate inflammatory cells through Toll-like receptor 2 (TLR2), suggesting that TLR2 could play a pivotal role in the host response to B. burgdorferi. TLR2 does play a critical role in host defense, as infected TLR2−/− mice harbored up to 100-fold more spirochetes in tissues than did TLR2+/+ littermates. Spirochetes persisted at extremely elevated levels in TLR2-deficient mice for at least 8 wk following infection. Infected TLR2−/− mice developed normal Borrelia-specific Ab responses, as measured by quantity of Borrelia-specific Ig isotypes, the kinetics of class switching to IgG, and the complexity of the Ags recognized. These findings indicate that the failure to control spirochete levels in tissues is not due to an impaired acquired immune response. While macrophages from TLR2−/− mice were not responsive to lipoproteins, they did respond to nonlipoprotein components of sonicated spirochetes. These TLR2-independent responses could play a role during the inflammatory response to B. burgdorferi, as infected TLR2−/− mice developed greater ankle swelling than wild-type littermates. Thus, while TLR2-dependent signaling pathways play a major role in the innate host defense to B. burgdorferi, both inflammatory responses and the development of the acquired humoral response can occur in the absence of TLR2.

Resistance to Lyme disease in decorin-deficient mice

Microbial adhesion to the host tissue represents an early, critical step in the pathogenesis of most infectious diseases. BORRELIA: burgdorferi, the causative agent of Lyme disease (LD), expresses two surface-exposed decorin-binding adhesins, DbpA and DbpB. A decorin-deficient (Dcn(-/-)) mouse was recently developed and found to have a relatively mild phenotype. We have now examined the process of experimental LD in Dcn(-/-) mice using both needle inoculation and tick transmission of spirochetes. When exposed to low doses of the infective agent, Dcn(-/-) mice had fewer Borrelia-positive cultures from most tissues analyzed than did Dcn(+/+) or Dcn(+/-) mice. When the infection dose was increased, similar differences were not observed in most tissues but were seen in bacterial colonization of joints and the extent of Borreila-induced arthritis. Quantitative PCR demonstrated that joints harvested from Dcn(-/-) mice had diminished Borrelia numbers compared with issues harvested from Dcn(+/+) controls. Histological examination also revealed a low incidence and severity of arthritis in Dcn(-/-) mice. Conversely, no differences in the numbers of Borreila-positive skin cultures were observed among the different genotypes regardless of the infection dose. These differences, which were observed regardless of genetic background of the mice (BALB/c or C3H/HeN) or method of infection, demonstrate the importance of decorin in the pathogenesis of LD.

Host-pathogen interactions promoting inflammatory Lyme arthritis: use of mouse models for dissection of disease processes.

Recent studies have confirmed the infectious and inflammatory nature of arthritis induced by Borrelia burgdorferi, or Lyme arthritis. This arthritis is directed by the presence of the bacteria in joint tissue, and is mediated through activation of the Toll-like receptor 2 (TLR2) signaling pathways by borrelial lipoproteins. Several host genes regulate the severity of arthritis, possibly by regulating the balance of pro- and anti-inflammatory responses.

The Moraxella catarrhalis Autotransporter McaP Is a Conserved Surface Protein That Mediates Adherence to Human Epithelial Cells through Its N-Terminal Passenger Domain

ABSTRACT The protein McaP was previously shown to be an adhesin expressed by the Moraxella catarrhalis strain O35E, which also displays esterase and phospholipase B activities (J. M. Timpe et al., Infect. Immun. 71:4341-4350, 2003). In the present study, sequence analysis suggests that McaP is a conventional autotransporter protein that contains a 12-stranded β-barrel transporter module (amino acids [aa] 383 to 650) linked to a surface-exposed passenger domain exhibiting lipolytic activity (aa 62 to 330). An in-frame deletion removing most of this predicted N-terminal passenger domain was engineered, and Escherichia coli expressing the truncated McaP protein exhibited greatly reduced adherence to A549 human lung epithelial cells compared to E. coli expressing wild-type McaP. Site-directed mutagenesis of a serine residue at position 62 of McaP, predicted to be important for the lipolytic activity of the protein, resulted in loss of hydrolysis of p-nitrophenyl ester of caproate. E. coli expressing this mutated McaP, however, adhered to A549 monolayers at levels greater than recombinant bacteria expressing the wild-type adhesin. These results indicate that the predicted passenger domain of McaP is involved in both the binding and the lipolytic activity of the molecule and demonstrate that the adhesive properties of McaP do not require its lipolytic activity. Sequence analysis of mcaP from eight Moraxella catarrhalis strains revealed that the gene product is highly conserved at the amino acid level (98 to 100% identity), and Western blot analysis demonstrated that a panel of 16 isolates all express McaP. Flow cytometry experiments using antibodies raised against various portions of McaP indicated that its predicted passenger domain as well as transporter module contain surface-exposed epitopes. In addition to binding to the surface of intact bacteria, these antibodies were found to decrease adherence of M. catarrhalis to A549 human lung cells by up to 47% and to reduce binding of recombinant E. coli expressing McaP by 98%. These results suggest that McaP should be considered as a potential vaccine antigen.

IL-10 Deficiency Promotes Increased Borrelia burgdorferi Clearance Predominantly through Enhanced Innate Immune Responses

Borrelia burgdorferi is capable of persistently infecting a variety of hosts despite eliciting potent innate and adaptive immune responses. Preliminary studies indicated that IL-10-deficient (IL-10−/−) mice exhibit up to 10-fold greater clearance of B. burgdorferi from target tissues compared with wild-type mice, establishing IL-10 as the only cytokine currently known to have such a significant effect on spirochetal clearance. To further delineate these IL-10-mediated immune effects, kinetic studies indicated that spirochete dissemination to target tissues is similar in both wild-type and IL-10−/− mouse strains, and that enhanced clearance of B. burgdorferi in IL-10−/− mice is correlated with increased B. burgdorferi-specific Ab as early as 2 wk postinfection. Immunoblot analysis indicated that Abs produced by infected IL-10−/− and wild-type mice recognize similar ranges of spirochetal Ags. Immune sera from IL-10−/− and wild-type mice also exhibited similar bactericidal activity in vitro, and passive transfer of these immune sera into B. burgdorferi-infected SCID mice caused similar reductions of bacterial numbers in target tissues. Infectious dose studies indicated that 8-fold more B. burgdorferi were needed to efficiently infect naive IL-10−/− mice, suggesting these animals possess higher innate barriers to infection. Moreover, macrophages derived from IL-10−/− mice exhibit enhanced proinflammatory responses to B. burgdorferi stimulation compared with wild-type controls, and these responses are not significantly affected by the presence of immune serum. These findings confirm that B. burgdorferi clearance by innate immune responses is more efficient in the absence of IL-10, and these activities are not directly related to increased levels of B. burgdorferi-specific Ab.

Effects of vlsE Complementation on the Infectivity of Borrelia burgdorferi Lacking the Linear Plasmid lp28-1

ABSTRACT The loss of linear plasmid lp28-1, which contains the vls antigenic variation locus, is associated with reduced infectivity of Borrelia burgdorferi in immunocompetent mice. The recombinant shuttle vector pBBE22, which includes the virulence determinant BBE22 from lp25 and restores infectivity to readily transformable B. burgdorferi lacking lp25 and lp56, was used to determine the effect of trans expression of vlsE on virulence. Spirochetes lacking lp28-1 were complemented with the plasmid pBBE22:vlsE, containing both BBE22 and vlsE. VlsE protein produced by this construct was expressed and surface accessible in in vitro-cultured B. burgdorferi, as determined by surface proteolysis and immunoblot analysis. Clones lacking lp25 but containing lp28-1 and either pBBE22 or pBBE22:vlsE were reisolated consistently from immunocompetent mice 8 weeks after infection. In contrast, a clone lacking both lp25 and lp28-1 and complemented with pBBE22:vlsE was isolated from only a single tissue of one of six C3H/HeN mice 8 weeks postinfection. These results indicate that either an intact vls antigenic variation locus or another determinant on lp28-1 is required to restore complete infectivity. In addition, an isogenic clone that retained lp28-1 was complemented with the vlsE shuttle plasmid and was examined for vlsE sequence variation and infectivity. Sequence variation was not observed for the shuttle plasmid, indicating that the cis arrangement of vlsE and the vls silent cassettes in lp28-1 facilitate vlsE gene conversion. Lack of vlsE sequence variation on the shuttle plasmid thus did not result in clearance of the trans-complemented strain in immunocompetent mice under the conditions tested.

Toll-like receptor 2 plays a pivotal role in host defense and inflammatory response to Borrelia burgdorferi.

275 BORRELIA BURGDORFERI infection of humans is a multisystem illness characterized by persistent bacterial infection and invasion of numerous tissues (Steere 2001). Arthritis can result from spirochete invasion of joint tissue, and is characterized by joint swelling, inflammatory infiltrate, and tendonitis. In most individuals, arthritis is treatable with antibiotics, with symptoms resolving after clearance of bacteria (Steere et al. 1987). Mice of certain inbred strains, including C3H, develop a subacute arthritis that models the arthritis in humans (Barthold et al. 1990). The subacute, infection-associated arthritis has been studied extensively in mice, and provides an excellent opportunity to understand the pathologic processes involved in arthritis development. Importantly, the subacute arthritis develops in mice lacking B and T lymphocytes and is therefore not autoimmune-mediated, nor does it require immune complexes (Barthold et al. 1992). The subacute arthritis of mice and humans is clearly different in mechanism from the treatmentresistant arthritis that develops in a small percentage of patients possessing particular MHC alleles that may be autoimmune-mediated (Steere et al. 1990). B. burgdorferi possess potent pro-inflammatory properties, which have been attributed to abundantly expressed outer surface lipoproteins (Radolf et al. 1991, Wooten and Weis 2001). These lipoproteins possess a tripalmitoyl-cysteinyl moiety on the amino terminus, characteristic of lipoproteins made by many bacterial species (Bessler et al. 1985). The identification of toll-like receptor (TLR) 2 as the signal transducing receptor for the lipoproteins helped to explain the inflammatory response associated with B. burgdorferi infection (Aliprantis et al. 1999, Brightbill et al. 1999, Hirschfeld et al. 1999). TLR2 is a member of an evolutionarily conserved family of pattern recognition molecules, first identified by homology with Drosophila toll (Medzhitov et al. 1997). Signaling through TLRs results in activation of a conserved signaling pathway that ultimately results in translocation of the transcription factor NF-kB to the nucleus and transcriptional activation of numerous genes including those encoding inflammatory cytokines, chemokines, and adhesion molecules (Medzhitov et al. 1997, Akira et al. 2001). Expression of these gene products is consistent with the localized inflammation characterized in tissues of animals

Viable Borrelia burgdorferi Enhances Interleukin-10 Production and Suppresses Activation of Murine Macrophages

ABSTRACT Although it is capable of eliciting strong innate and adaptive immune responses, Borrelia burgdorferi often evades immune clearance through largely unknown mechanisms. Our previous studies determined that infected interlukin-10−/− (IL-10−/−) mice show significantly lower B. burgdorferi levels than wild-type (B6) mice and that IL-10 inhibits innate immune responses critical for controlling B. burgdorferi infection. To determine whether virulent B. burgdorferi preferentially enhances IL-10 production, we developed an in vitro coculture medium (RPMI.B) in which both B. burgdorferi and primary macrophages (Mφs) remain viable. B. burgdorferi grew at similar rates and was able to regulate expression of immunoreactive proteins with similar kinetics in RPMI.B and in traditional BSK medium; in contrast, B. burgdorferi cultured in conventional tissue culture medium (RPMI) rapidly lost viability. Coculture of viable B. burgdorferi in RPMI.B with Mφs resulted in more rapid and significant increases in IL-10 transcripts and secreted proteins than coculture with nonviable B. burgdorferi in RPMI, which corresponded with decreased production of proinflammatory cytokines. Addition of live B. burgdorferi to Mφs in RPMI.B also elicited substantially higher IL-10 levels than heat-killed bacteria elicited, confirming that increased IL-10 production was not inherent to coculture in RPMI.B. Transfer of supernatants from B. burgdorferi-stimulated Mφs into naïve Mφ cultures resulted in suppressed activation upon subsequent stimulation with different bacterial agonists, and this suppression was obviated by IL-10-specific antibody. In vivo analyses determined that murine skin samples exhibited substantial upregulation of IL-10 within 24 h of injection of B. burgdorferi. Together, these results suggest that viable B. burgdorferi can suppress early Mφ responses during infection by causing increased release of IL-10.

Effect of complement component C3 deficiency on experimental Lyme borreliosis in mice.

ABSTRACT Mice deficient in complement component C3 (C3−/−) and syngeneic C57BL/6 control mice were challenged with Borrelia burgdorferi to determine the role of complement in immune clearance and joint histopathology during experimental Lyme borreliosis. Tibiotarsal joint, ear, and heart tissues were monitored for spirochete numbers at 2, 4, 8, and 12 weeks postinoculation with 105B. burgdorferi B31 clone 5A4 by using quantitative real-time PCR. The spirochete load in joint and ear tissue remained higher in the C3−/− mice than in the wild-type counterparts throughout the 12-week study, whereas the numbers in heart tissue of both groups of mice decreased substantially at 8 to 12 weeks postinfection. Histopathology scores for joint tissue were generally higher in the C3−/− mice compared to C57BL/6 controls at 2 and 4 weeks postinfection, which may reflect the presence of higher numbers of bacteria in the joints at these early time points. Levels of anti-B. burgdorferi immunoglobulin G tended to be reduced in the C3−/− mice compared to control mice. Furthermore, a 5.5-fold-lower number of the complement-sensitive Borrelia garinii was needed to infect C3−/− mice compared to C57BL/6 mice, indicating that its sensitivity to complement is one barrier to infection of the mouse model by B. garinii. These results indicate that the complement system may be important in controlling the early dissemination and progression of B. burgdorferi infection.

Tripalmitoyl-S-Glyceryl-Cysteine-Dependent OspA Vaccination of Toll-Like Receptor 2-Deficient Mice Results in Effective Protection from Borrelia burgdorferi Challenge

ABSTRACT Toll-like receptor 2 (TLR2) is a transmembrane signal transducer for tripalmitoyl-S-glyceryl-cysteine (Pam3Cys)-modified lipoproteins, including OspA from the Lyme disease spirochete Borrelia burgdorferi. The Pam3Cys modification provides adjuvant activity for inducing humoral responses, suggesting that TLR2 could function as the adjuvant receptor for the OspA vaccine. The importance of TLR2 in the humoral response to OspA was confirmed, because overall levels of immunoglobulin G (IgG) were reduced in TLR2-deficient mice, when compared with those in wild-type mice. However, the levels of production of IgG1 were similar in both mouse strains, and the levels of induction of protective immunity were comparable. Unlipidated OspA was not immunogenic in wild-type or TLR2-deficient mice, indicating the lipid modification was active in the absence of TLR2. These findings indicate that the Pam3Cys modification of bacterial lipoprotein has adjuvant properties independent of TLR2 signaling.