Immunity to Lyme disease: protection, pathology and persistence

Characterization of unique regions of Borrelia burgdorferi surface-located membrane protein 1

The pathogen of Lyme disease, Borrelia burgdorferi, produces a putative surface protein termed "surface-located membrane protein 1" (Lmp1). Lmp1 has been shown previously to assist the microbe in evasion of host-acquired immune defenses and in the establishment of persistent infection of mammals. Here, we show that Lmp1 is an integral membrane protein with surface-exposed N-terminal, middle, and C-terminal regions. During murine infection, antibodies recognizing these three protein regions were produced. Separate immunization of mice with each of the discrete regions exerted differential effects on spirochete survival during infection. Notably, antibodies against the C-terminal region primarily interfered with B. burgdorferi persistence in the joints, while antibodies specific to the N-terminal region predominantly affected pathogen levels in the heart, including the development of carditis. Genetic reconstitution of lmp1 deletion mutants with the lmp1 N-terminal region significantly enhanced its ability to resist the bactericidal effects of immune sera and also was observed to increase pathogen survival in vivo. Taken together, the combined data suggest that the N-terminal region of Lmp1 plays a distinct role in spirochete survival and other parts of the protein are related to specific functions corresponding to pathogen persistence and tropism during infection that is displayed in an organ-specific manner. The findings reported here underscore the fact that surface-exposed regions of Lmp1 could potentially serve as vaccine targets or antigenic regions that could alter the course of natural Lyme disease.

The majority of cutaneous marginal zone B-cell lymphomas expresses class-switched immunoglobulins and develops in a T-helper type 2 inflammatory environment

Extranodal marginal zone B-cell lymphomas (MZBCLs) arise on a background of chronic inflammation resulting from organ-specific autoimmunity, infection, or by unknown causes. Well-known examples are salivary gland MZBCL in Sjögren's sialadenitis and gastric MZBCL in Helicobacter pylori gastritis. MZBCLs express CXCR3, a receptor for interferon-γ–induced chemokines highly expressed in the chronic inflammatory environment. The immunoglobulin (Ig) variable heavy/light chain (IgVH/IgVL) gene repertoire of salivary gland and gastric MZBCL appears restricted and frequently encodes B-cell receptors with rheumatoid factor reactivity. Primary cutaneous marginal zone B-cell lymphomas (PCMZLs) are regarded as the skin-involving counterparts of extranodal MZBCLs. Although PCMZLs have been associated with Borrelia burgdorferi dermatitis, PCMZLs generally arise because of unknown causes. We studied an extensive panel of PCMZLs and show that PCMZLs do not conform to the general profile of extranodal MZBCL. Whereas most noncutaneous MZBCLs express IgM, PCMZLs in majority express IgG, IgA, and IgE and do not show an obvious immunoglobulin repertoire bias. Furthermore, the isotype-switched PCMZLs lack CXCR3 and seem to arise in a different inflammatory environment, compared with other extranodal MZBCLs.

Common and unique contributions of decorin-binding proteins A and B to the overall virulence of Borrelia burgdorferi

As an extracellular bacterium, the Lyme disease spirochete Borrelia burgdorferi resides primarily in the extracellular matrix and connective tissues and between host cells during mammalian infection, where decorin and glycosaminoglycans are abundantly found, so its interactions with these host ligands potentially affect various aspects of infection. Decorin-binding proteins (Dbps) A and B, encoded by a 2-gene operon, are outer surface lipoproteins with similar molecular weights and share approximately 40% identity, and both bind decorin and glycosaminoglycans. To investigate how DbpA and DbpB contribute differently to the overall virulence of B. burgdorferi, a dbpAB mutant was modified to overproduce the adhesins. Overproduction of either DbpA or DbpB resulted in restoration of the infectivity of the mutant to the control level, measured by 50% infectious dose (ID(50)), indicating that the two virulence factors are interchangeable in this regard. Overproduction of DbpA also allowed the mutant to disseminate to some but not all distal tissues slightly slower than the control, but the mutant with DbpB overproduction showed severely impaired dissemination to all tissues that were analyzed. The mutant with DbpA overproduction colonized all tissues, albeit generating bacterial loads significantly lower than the control in heart and joint, while the mutant overproducing DbpB remained severely defective in heart colonization and registered bacterial loads substantially lower than the control in joint. Taken together, the study indicated that DbpA and DbpB play a similar role in contribution to infectivity as measured by ID(50) value but contribute differently to dissemination and tissue colonization.

The failure of immune response evasion by linear plasmid 28-1-deficient Borrelia burgdorferi is attributable to persistent expression of an outer surface protein

Infectivity and persistence by Borrelia burgdorferi, the etiologic agent of Lyme disease, rely stringently on regulatory events. Among these is the downregulation of lipoprotein antigen expression, exemplified by outer surface protein C (OspC), at the advent of specific immunity in the mammalian host. B. burgdorferi spirochetes that lack the linear plasmid 28-1 (lp28-1) succumb to the host's immune response. We thus explored the notion that these two phenomena were related--that lp28-1(-) organisms fail to downregulate ospC and thus are cleared following the appearance of anti-OspC antibody in the murine host. The lp-28-1(-) isolate and a wild-type (wt) isolate bearing the complete set of plasmids were grown in dialysis membrane chambers that were implanted into rat peritoneal cavities. Analysis of mRNA and protein from these cultures showed that OspC expression levels by lp28-1(-) organisms are abnormally high in vivo. A time course analysis of ospC expression in tissues following infection indicates also that temporal diminution of the dominant antigen OspC is impaired in lp28-1(-) spirochetes. Finally, passive transfer of monoclonal OspC-specific antibody into SCID mice 8 days postinfection cleared lp28-1(-) spirochetes, yet the wt organisms persisted in a majority of animals. These findings indicate that incomplete repression of OspC by lp28-1(-) organisms renders them susceptible to immune-mediated clearance. The lp28-1 plasmid must harbor one or more genes involved in OspC downregulation.

Verification and dissection of the ospC operator by using flaB promoter as a reporter in Borrelia burgdorferi

The Lyme disease spirochete Borrelia burgdorferi must repress expression of outer surface protein C (OspC) to effectively evade specific humoral immunity and to establish persistent infection. This ability largely relies upon a regulatory element, the only operator that has been reported in spirochetal bacteria. Immediately upstream of the ospC promoter, two sets of inverted repeats (IRs) constitute small and large palindromes, in which the right IR of the large palindrome contains the left IR of the small one, and may collectively function as the ospC operator. In the study, the large palindrome with or without the small IR was fused with an flaB promoter, which was used to drive expression of a promoterless ospC copy as a reporter gene, and introduced into OspC-deficient B. burgdorferi. The presence of the large palindrome alone significantly reduced ospC expression driven by the fused flaB promoter in the joint tissue of severe combined immunodeficiency (SCID) mice, and rescued spirochetes from elimination by passively transferred OspC antibody in infected SCID mice and specific immune responses elicited in immunocompetent mice, confirming a function of the IRs as an operator. Inclusion of the small IR further enhanced the ability of the large palindrome to reduce the activity of the fused flaB promoter, indicating that the small IR is a part of the operator. Taken together, the study led to successful verification and dissection of the ospC operator.

Both decorin-binding proteins A and B are critical for the overall virulence of Borrelia burgdorferi

Both decorin-binding proteins (DbpA and DbpB) of the Lyme disease spirochete Borrelia burgdorferi bind decorin and glycosaminoglycans, two important building blocks of proteoglycans that are abundantly found in the extracellular matrix (ECM) and connective tissues as well as on cell surfaces of mammals. As an extracellular pathogen, B. burgdorferi resides primarily in the ECM and connective tissues and between host cells during mammalian infection. The interactions of B. burgdorferi with these host ligands mediated by DbpA and DbpB potentially influence various aspects of infection. Here, we show that both DbpA and DbpB are critical for the overall virulence of B. burgdorferi in the murine host. Disruption of the dbpBA locus led to nearly a 10(4)-fold increase in the 50% infectious dose (ID50). Complementation of the mutant with either dbpA or dbpB reduced the ID50 from over 10(4) to roughly 10(3) organisms. Deletion of the dbpBA locus affected colonization in all tissues of infected mice. The lack of dbpA alone precluded the pathogen from colonizing the heart tissue, and B. burgdorferi deficient for DbpB was recovered only from 42% of the heart specimens of infected mice. Although B. burgdorferi lacking either dbpA or dbpB was consistently grown from joint specimens of almost all infected mice, it generated bacterial loads significantly lower than the control. The deficiency in either DbpA or DbpB did not reduce the bacterial load in skin, but lack of both significantly did. Taken together, the study results indicate that neither DbpA nor DbpB is essential for mammalian infection but that both are critical for the overall virulence of B. burgdorferi.

Increasing the interaction of Borrelia burgdorferi with decorin significantly reduces the 50 percent infectious dose and severely impairs dissemination

Tight regulation of surface antigenic expression is crucial for the pathogenic strategy of the Lyme disease spirochete, Borrelia burgdorferi. Here, we report the influence of increasing expression of decorin-binding protein A (DbpA), one of the most investigated spirochetal surface adhesins, on the 50% infectious dose (ID(50)), dissemination, tissue colonization, pathogenicity, and persistence of B. burgdorferi in the murine host. Our in vitro assays showed that increasing DbpA expression dramatically increased the interaction of B. burgdorferi with decorin and sensitivity to growth inhibition/killing by anti-DbpA antibodies; however, this increased interaction did not affect spirochetal growth and replication in the presence of decorin. Increasing DbpA expression significantly reduced ID(50) values and severely impaired dissemination in severe combined immunodeficiency (SCID) and immunocompetent mice. During infection of SCID mice, B. burgdorferi with increased DbpA expression was able to effectively colonize heart and skin tissues, but not joint tissues, completely abrogating arthritis virulence. Although increasing DbpA expression did not affect spirochetal persistence in the skin, it diminished the ability of B. burgdorferi to persist in the heart and joint tissues during chronic infection of immunocompetent mice. Taken together, the study highlights the importance of controlling surface antigen expression in the infectivity, dissemination, tissue colonization, pathogenicity, and persistence of B. burgdorferi during mammalian infection.

Identification of an ospC operator critical for immune evasion of Borrelia burgdorferi

Timely expression of the outer surface protein C (OspC) is crucial for the pathogenic strategy of the Lyme disease spirochete Borrelia burgdorferi. The pathogen abundantly expresses OspC during initial infection when the antigen is required, but downregulates when its presence poses a threat to the spirochetes once the anti-OspC humoral response has developed. Here, we show that a large palindromic sequence immediately upstream of the ospC promoter is essential for the repression of ospC expression during murine infection and for the ability of B. burgdorferi to evade specific OspC humoral immunity. Deletion of the sequence completely diminished the ability of B. burgdorferi to avoid clearance by transferred OspC antibody in SCID mice. B. burgdorferi lacking the regulatory element was able to initiate infection but unable to persist in immunocompetent mice. Taken together, the regulatory element immediately upstream of the ospC promoter serves as an operator that may interact with an unidentified repressor(s) to negatively regulate ospC expression and is essential for the immune evasion of B. burgdorferi.

Mycosis fungoides: is it a Borrelia burgdorferi-associated disease?

Mycosis fungoides (MF) is the most frequently found cutaneous T-cell lymphoma with an unknown aetiology. Several aetiopathogenetic mechanisms have been postulated, including persistent viral or bacterial infections. We looked for evidence of Borrelia burgdorferi (Bb), the aetiologic agent of Lyme disease (LD), in a case study of MF patients from Northeastern Italy, an area with endemic LD. Polymerase chain reaction for the flagellin gene of Bb was used to study formalin-fixed paraffin-embedded lesional skin biopsies from 83 patients with MF and 83 sex- and age-matched healthy controls with homolocalised cutaneous nevi. Borrelia burgdorferi-specific sequence was detected in 15 out of 83 skin samples of patients with MF (18.1%), but in none out of 83 matched healthy controls (P<0.0001). The Bb positivity rates detected in this study support a possible role for Bb in the aetiopathogenesis of MF in a population endemic for LD.

Treatment of Lyme disease: a medicolegal assessment

Lyme disease is the most common tick-borne disease in the world today. Despite extensive research into the complex nature of Borrelia burgdorferi, the spirochetal agent of Lyme disease, controversy continues over the diagnosis and treatment of this protean illness. This report will focus on two aspects of the treatment of Lyme disease. First, the medical basis for diagnostic and therapeutic uncertainty in Lyme disease, including variability in clinical presentation, shortcomings in laboratory testing procedures, and design defects in therapeutic trials. Second, the standard of care and legal issues that have resulted from the clinical uncertainty of Lyme disease diagnosis and treatment. Specifically, the divergent therapeutic standards for Lyme disease are addressed, and the difficult process of creating treatment guidelines for this complex infection is explored. Consideration by healthcare providers of the medicolegal issues outlined in this review will support a more rational approach to the diagnosis and treatment of Lyme disease and related tick-borne illnesses.

Borrelia burgdorferi changes its surface antigenic expression in response to host immune responses

The Lyme disease spirochete, Borrelia burgdorferi, causes persistent mammalian infection despite the development of vigorous immune responses against the pathogen. To examine spirochetal phenotypes that dominate in the hostile immune environment, the mRNA transcripts of four prototypic surface lipoproteins, decorin-binding protein A (DbpA), outer surface protein C (OspC), BBF01, and VlsE, were analyzed by quantitative reverse transcription-PCR under various immune conditions. We demonstrate that B. burgdorferi changes its surface antigenic expression in response to immune attack. dbpA expression was unchanged while the spirochetes decreased ospC expression by 446 times and increased BBF01 and vlsE expression up to 20 and 32 times, respectively, under the influence of immune pressure generated in immunocompetent mice during infection. This change in antigenic expression could be induced by passively immunizing infected severe combined immunodeficiency mice with specific Borrelia antisera or OspC antibody and appears to allow B. burgdorferi to resist immune attack.

Outer membrane proteins of pathogenic spirochetes

Pathogenic spirochetes are the causative agents of several important diseases including syphilis, Lyme disease, leptospirosis, swine dysentery, periodontal disease and some forms of relapsing fever. Spirochetal bacteria possess two membranes and the proteins present in the outer membrane are at the site of interaction with host tissue and the immune system. This review describes the current knowledge in the field of spirochetal outer membrane protein (OMP) biology. What is known concerning biogenesis and structure of OMPs, with particular regard to the atypical signal peptide cleavage sites observed amongst the spirochetes, is discussed. We examine the functions that have been determined for several spirochetal OMPs including those that have been demonstrated to function as adhesins, porins or to have roles in complement resistance. A detailed description of the role of spirochetal OMPs in immunity, including those that stimulate protective immunity or that are involved in antigenic variation, is given. A final section is included which covers experimental considerations in spirochetal outer membrane biology. This section covers contentious issues concerning cellular localization of putative OMPs, including determination of surface exposure. A more detailed knowledge of spirochetal OMP biology will hopefully lead to the design of new vaccines and a better understanding of spirochetal pathogenesis.

Protective niche for Borrelia burgdorferi to evade humoral immunity

The Lyme disease spirochete, Borrelia burgdorferi, is an extracellular microbe that causes persistent infection despite the development of strong immune responses against the bacterium. B. burgdorferi expresses several ligand-binding lipoproteins, including the decorin-binding proteins (Dbps) A and B, which may mediate attachment to decorin, a major component of the host extracellular matrix during murine infection. We show that B. burgdorferi was better protected in the joints and skin, two tissues with a higher decorin expression, than in the urinary bladder and heart, two tissues with a lower decorin expression, during chronic infection of wild-type mice. Targeted disruption of decorin alone completely abolished the protective niche in chronically infected decorin-deficient mice but did not affect the spirochete burden during early infection. The nature of protection appeared to be specific because the spirochetes with higher outer surface protein C expression were not protected while the protective niche seemed to favor the spirochetes with a higher dbpA expression during chronic infection. These data suggest that spirochetal DbpA may interact with host decorin during infection and such interactions could be a mechanism that B. burgdorferi uses to evade humoral immunity and establish chronic infection.

Phenotypes indicating cytolytic properties of Borrelia-specific interferon-gamma secreting cells in chronic Lyme neuroborreliosis

The immuno-pathogenetic mechanisms underlying chronic Lyme neuroborreliosis are mainly unknown. Human Borrelia burgdorferi (Bb) infection is associated with Bb-specific secretion of interferon-gamma (IFN-gamma), which may be important for the elimination of Bb, but this may also cause tissue injury. In order to increase the understanding of the pathogenic mechanisms in chronic neuroborreliosis, we investigated which cell types that secrete IFN-gamma. Blood mononuclear cells from 13 patients with neuroborreliosis and/or acrodermatitis chronicum atrophicans were stimulated with Bb antigen and the phenotypes of the induced IFN-gamma-secreting cells were analyzed with three different approaches. Cells expressing CD8 or TCRgammadelta, which both have cytolytic properties, were the main phenotypes of IFN-gamma-secreting cells, indicating that tissue injury in chronic neuroborreliosis may be mediated by cytotoxic cells.

Borrelia burgdorferi-induced tolerance as a model of persistence via immunosuppression

If left untreated, infection with Borrelia burgdorferi sensu lato may lead to chronic Lyme borreliosis. It is still unknown how this pathogen manages to persist in the host in the presence of competent immune cells. It was recently reported that Borrelia suppresses the host's immune response, thus perhaps preventing the elimination of the pathogen (I. Diterich, L. Härter, D. Hassler, A. Wendel, and T. Hartung, Infect. Immun. 69:687-694, 2001). Here, we further characterize Borrelia-induced immunomodulation in order to develop a model of this anergy. We observed that the different Borrelia preparations that we tested, i.e., live, heat-inactivated, and sonicated Borrelia, could desensitize human blood monocytes, as shown by attenuated cytokine release upon restimulation with any of the different preparations. Next, we investigated whether these Borrelia-specific stimuli render monocytes tolerant, i.e. hyporesponsive, towards another Toll-like receptor 2 (TLR2) agonist, such as lipoteichoic acid from gram-positive bacteria, or towards the TLR4 agonist lipopolysaccharide. Cross-tolerance towards all tested stimuli was induced. Furthermore, using primary bone marrow cells from TLR2-deficient mice and from mice with a nonfunctional TLR4 (strain C3H/HeJ), we demonstrated that the TLR2 was required for tolerance induction by Borrelia, and using neutralizing antibodies, we identified interleukin-10 as the key mediator involved. Although peripheral blood mononuclear cells tolerized by Borrelia exhibited reduced TLR2 and TLR4 mRNA levels, the expression of the respective proteins on monocytes was not decreased, ruling out the possibility that tolerance to Borrelia is attributed to a reduced TLR2 expression. In summary, we characterized tolerance induced by B. burgdorferi, describing a model of desensitization which might mirror the immunosuppression recently attributed to the persistence of Borrelia in immunocompetent hosts.

Hyporesponsiveness to vaccination with Borrelia burgdorferi OspA in humans and in TLR1- and TLR2-deficient mice

The Lyme disease vaccine is based on the outer-surface lipoprotein (OspA) of the pathogen Borrelia burgdorferi, and 95% of vaccine recipients develop substantial titers of antibodies against OspA. Here, we identified seven individuals with very low antibody titers after vaccination (low responders). The macrophages of low responders produced less tumor necrosis factor-alpha and interleukin-6 after OspA stimulation and had lower cell-surface expression of Toll-like receptor (TLR) 1 as compared to normal cells, but normal expression of TLR2. TLRs activate innate responses to pathogens, and TLR2 recognizes lipoproteins and peptidoglycan (PGN). After OspA immunization, mice genetically deficient in either TLR2 (TLR2(-/-)) or TLR1 (TLR1(-/-)) produced low titers of antibodies against OspA. Notably, macrophages from TLR2(-/-) mice were unresponsive to OspA and PGN, whereas those from TLR1(-/-) mice responded normally to PGN but not to OspA. These data indicate that TLR1 and TLR2 are required for lipoprotein recognition and that defects in the TLR1/2 signaling pathway may account for human hyporesponsiveness to OspA vaccination.

A role for peripheral blood fibrocytes in Lyme disease?

It is proposed that peripheral blood fibrocytes will be a new and important player in the pathogenesis of Lyme disease. Peripheral blood fibrocytes are a circulating leukocyte subpopulation that: (a) express collagen; (b) are an abundant source of cytokines, chemoattractants and growth factors; and (c) are able to recruit and activate naive T-cells and memory T-cells. We predict that peripheral blood fibrocytes will represent a new and important antigen-presenting cell which will play an important role in directing the immune response from the pathogenic Th1 to the protective Th2 response cell in Borrelia infections.

An immune evasion mechanism for spirochetal persistence in Lyme borreliosis

Borrelia burgdorferi, the Lyme disease spirochete, persistently infects mammalian hosts despite the development of strong humoral responses directed against the pathogen. Here we describe a novel mechanism of immune evasion by B. burgdorferi. In immunocompetent mice, spirochetes that did not express ospC (the outer-surface protein C gene) were selected within 17 d after inoculation, concomitantly with the emergence of anti-OspC antibody. Spirochetes with no detectable OspC transcript that were isolated from immunocompetent mice reexpressed ospC after they were either cultured in vitro or transplanted to naive immunocompetent mice, but not in OspC-immunized mice. B. burgdorferi persistently expressed ospC in severe combined immune-deficient (SCID) mice. Passive immunization of B. burgdorferi-infected SCID mice with an anti-OspC monoclonal antibody selectively eliminated ospC-expressing spirochetes but did not clear the infection. OspC-expressing spirochetes reappeared in SCID mice after the anti-OspC antibody was eliminated. We submit that selection of surface-antigen nonexpressers is an immune evasion mechanism that contributes to spirochetal persistence.

Characterization of surface antigen from Lyme disease spirochete Borrelia burgdorferi

Borrelia burgdorferi, the Lyme disease spirochete, possesses a surface protein, VlsE (variable major protein-like sequence, expressed), that undergoes antigenic variation. Unlike conserved regions of other proteins involved in antigenic variation, the most conserved invariable region of VlsE is immunodominant in Lyme-disease patients. Physicochemical analyses of pure recombinant VlsE yielded the following results: The protein appeared oligomeric in solution, with a secondary structure dominated by alpha-helices. Thermal denaturation (pH 7) probed by calorimetry involved two transitions: oligomer-to-monomer conversion (around 40 degrees C) followed by protein unfolding (55 +/- 1 degrees C). Chemical denaturation monitored by far-UV circular dichroism (20 degrees C, pH 7) sensed only polypeptide unfolding and took place in a single transition (Delta G(U)(H(2)O) = 23 +/- 2 kJ/mol). VlsE did not adopt a native structure at pH 3; at pH 10 the stability was significantly reduced. Knowledge of biophysical properties of VlsE may aid in understanding the mechanism of VlsE antigenic variation in B. burgdorferi.

Induction of strong hepatitis B virus (HBV) specific T helper cell and cytotoxic T lymphocyte responses by therapeutic vaccination in the trimera mouse model of chronic HBV infection

Humanized BALB/c mice (termed trimera mice) conditioned by lethal total body irradiation and bone marrow transplantation from SCID mice have been described to support rapid engraftment of human peripheral blood mononuclear cells (PBMC) and the induction of strong B and T cell responses after immunization in vivo. Moreover, these mice can be infected with the hepatitis B and C viruses (HBV, HCV). The current study employed this model to study therapeutic vaccination approaches against the HBV. Thus, strong primary Th cell responses against the HBV core (HBc) and the Borrelia burgdorferi control antigen were induced by transfer of antigen-loaded dendritic cells together with autologous PBMC from HBV-naive donors as well as by vaccination with high doses of antigen or a DNA plasmid encoding for HBcAg. Moreover, primary peptide-specific CTL responses against the immunodominant epitope HBc(18 - 27) were induced by HBc particle or DNA vaccination of chimera engrafted with HBV-naive PBMC. Finally, strong HBc-specific Th cell and antibody responses were induced by HBc or DNA vaccination of mice reconstituted with PBMC from a chronic HBV patient. Thus, since HBc represents the immunodominant antigen in self-limited HBV infection, HBc particles or DNA vectors are good candidates for therapeutic vaccination, that will be further studied in our model and clinical studies.

Dissociation of infectivity and pathogenicity in Borrelia burgdorferi

Clonal Borrelia burgdorferi N40 (cN40) passaged 75 times in vitro (N40-75) infects mice but does not cause disease. N40-75 passaged 45 times further in vitro (N40-120) was no longer infectious and lacked genes encoded on linear plasmids 38 and 28-1, among other differences. These data suggest that B. burgdorferi cN40, N40-75, and N40-120 have distinct phenotypes that can be used to dissect the genetic elements responsible for pathogenicity and infectivity.

Modulation of cytokine release in ex vivo-stimulated blood from borreliosis patients

In lipopolysaccharide-stimulated blood from 71 late-stage borreliosis patients, the ex vivo cytokine release capacity of tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) was reduced to 28% +/- 5% and to 31% +/- 5% (P < or = 0.001), respectively, compared to that of 24 healthy controls. White blood cell counts were normal in both groups. To investigate direct interactions between the pathogen and the immune cells, blood from healthy controls was exposed in vitro to live or heat-killed Borrelia or to Borrelia lysate. Compared to the pattern induced by bacterial endotoxins, a reduced release of TNF-alpha and IFN-gamma and an enhanced secretion of interleukin-10 and granulocyte colony-stimulating factor was found. In blood from 10 borreliosis patients stimulated with Borrelia lysate, TNF-alpha formation was decreased to 31% +/- 14% and IFN-gamma formation was decreased to 8% +/- 3% (P < or = 0.001) compared to the cytokine response of blood from healthy controls (n = 24). We propose to consider anti-inflammatory changes in the blood cytokine response capacity elicited by Borrelia as a condition that might favor the persistence of the spirochete.

Cutting edge: CD1d deficiency impairs murine host defense against the spirochete, Borrelia burgdorferi

CD1 molecules can present microbial lipid Ag to T cells, suggesting that they participate in host defense against pathogens. In this study, we examined the role of CD1d in resistance to infection with the Lyme disease spirochete, Borrelia burgdorferi (Bb), an organism with proinflammatory lipid Ag. Bb infection of CD1d-deficient (CD1d(-/-)) mouse strains normally resistant to this pathogen resulted in arthritis. Pathology correlated with an increased prevalence of spirochete DNA in tissues and enhanced production of Bb-specific IgG, including IgG to Ag rapidly down-modulated on spirochetes in vivo. CD1d(-/-) mice exhibited high-titer Bb-specific IgG2a, an isotype commonly induced in disease-susceptible mice but not in the disease-resistant control mice in this study. These results show that CD1d deficiency impairs host resistance to a spirochete pathogen, and are the first example of a mutation that imparts Bb-resistant mice with the Ab and disease profile of a susceptible mouse strain.

Cryptic and exposed invariable regions of VlsE, the variable surface antigen of Borrelia burgdorferi sl

Borrelia burgdorferi, the Lyme disease spirochete, possesses a surface protein, VlsE, which undergoes antigenic variation. VlsE contains two invariable domains and a variable one that includes six variable and six invariable regions (IRs). Five of the IRs are conserved among strains and genospecies of B. burgdorferi sensu lato. IR(6) is conserved, immunodominant, and exposed at the VlsE surface but not at the spirochete surface, as assessed in vitro. In the present study, the remaining conserved IRs (IR(2) to IR(5)) were investigated. Antisera to synthetic peptides based on each of the IR(2) to IR(5) sequences were produced in rabbits. Antipeptide antibody titers were similarly high in all antisera. Native VlsE was immunoprecipitable with antibodies to IR(2), IR(4), and IR(5) but not to IR(3), indicating that the first three sequences were exposed at the VlsE surface. However, negative surface immunofluorescence and in vitro antibody-mediated killing results indicated that none of the IRs were accessible to antibody at the spirochetal surface in vitro.

PCR-Based quantification of Borrelia burgdorferi organisms in canine tissues over a 500-Day postinfection period

Borrelia burgdorferi infection in beagle dogs was studied quantitatively with skin punch biopsy samples and blood samples collected at 4- and 2-week intervals, respectively, over a 500-day period. Thereafter, 25 tissue samples of each dog were collected for further analysis. Starting at day 120 after tick challenge, 12 dogs were treated with antibiotics (azithromycin, ceftriaxone, or doxycycline) for 30 consecutive days. Four dogs received no antibiotic therapy. Quantification of B. burgdorferi DNA was done with an ABI Prism 7700 Sequence Detection System with oligonucleotide primers and a fluorescence-labeled probe designed to specifically amplify a fragment of the ospA gene of B. burgdorferi strain N40. All 16 dogs became infected with B. burgdorferi after tick challenge. In skin biopsy samples, spirochete numbers peaked at day 60 postinfection (<1.5 x 10(6) organisms per 100 microgram of extracted DNA), at the same time when clinical signs of arthritis developed in 11 of 16 dogs, and decreased to almost undetectable levels during the following 6 months. The number of B. burgdorferi organisms detected in skin biopsy samples was inversely correlated with the antibody levels measured by enzyme-linked immunosorbent assay. Antibiotic treatment reduced the amount of detectable spirochete DNA in skin tissue by a factor of 1,000 or more. At the end of the experiment, B. burgdorferi DNA was detectable at low levels (10(2) to 10(4) organisms per 100 microgram of extracted DNA) in multiple tissue samples regardless of treatment. However, more tissue samples of untreated dogs than of antibiotic-treated dogs were positive, and tissue samples of untreated dogs also were positive by culture. Only 1.6% of 576 blood samples of all dogs were positive for B. burgdorferi by PCR.

The Lyme disease vaccine: conception, development, and implementation

In the past 20 years, remarkable strides have been made toward understanding and preventing Lyme disease in humans. In December 1998, the U.S. Food and Drug Administration approved a recombinant outer surface protein A vaccine against Lyme disease (LYMErix, SmithKline Beecham, Philadelphia, Pennsylvania). The vaccine, which is derived from a lipidated outer surface protein of the causative spirochete Borrelia burgdorferi, is important because it may decrease the morbidity and financial costs associated with Lyme disease. Its mechanism is unique because it works inside the tick vector itself, preventing the human from becoming infected.

Neutrophil activation by bacterial lipoprotein versus lipopolysaccharide: differential requirements for serum and CD14

Neutrophil activation plays an important role in the inflammatory response to Gram-negative bacterial infections. LPS has been shown to be a major mediator of neutrophil activation which is accompanied by an early down-regulation of L-selectin and up-regulation of CD1lb/CD18. In this study, we investigated whether lipoprotein (LP), the most abundant protein in the outer membrane of bacteria from the family Enterobacteriaceae, can activate neutrophils and whether this activation is mediated by mechanisms that differ from those used by LPS or Escherichia coli diphosphoryl lipid A (EcDPLA). Neutrophil activation was assessed by measuring down-regulation of L-selectin and up-regulation of CD11b/CD18. When comparing molar concentrations of LP vs EcDPLA, LP was more potent (four times) at activating neutrophils. In contrast to LPS/EcDPLA, LP activation of neutrophils was serum independent. However, LP activation of neutrophils was enhanced by the addition of soluble CD14 and/or LPS-binding protein. In the presence of serum, LP activation of neutrophils was inhibited by different mAbs to CD14. This inhibition was significantly reduced or absent when performed in the absence of serum. Diphosphoryl lipid A from Rhodobacter spheroides (RaDPLA) completely inhibited LPS/EcDPLA activation of neutrophils but only slightly inhibited LP activation of neutrophils. These results suggest that LP activation of human neutrophils can be mediated by a mechanism that is different from LPS activation and that LP is a potentially important component in the development of diseases caused by Gram-negative bacteria of the family Enterobacteriaceae.

Eradication of Borrelia burgdorferi infection in primary marginal zone B-cell lymphoma of the skin

Primary cutaneous B-cell lymphomas have been associated with Borrelia burgdorferi, the spirochete responsible for Lyme disease. Recently, cutaneous marginal zone B-cell lymphoma has been proposed as a distinct clinical-pathological entity. We report a case of primary cutaneous marginal zone lymphoma, associated with B burgdorferi infection. Polymerase chain reaction (PCR) amplification of the third complementarity determining region (CDR3) of the immunoglobulin heavy chain gene showed the presence of a monoclonal lymphoproliferation, therefore strengthening the histological diagnosis of a malignant process. B burgdorfer-specific hbb gene sequences were detected by PCR in the lymphoma tissue at diagnosis but not after antibiotic treatment. A nearly complete clinical and histological regression was observed after B burgdorferi eradication, with immunohistochemistry studies showing disappearance of plasma cell differentiation and a marked decline in the number of CD3+ T cells and Ki-67+ cells. Our case confirms the link between B burgdorferi and some cutaneous lymphomas. The disappearance of the microorganism accompanied by the unequivocal decrease of most indicators of active T- and B-cell immune response strongly supported a pathogenetic role for B burgdorferi in sustaining an antigen-driven development and growth of this cutaneous marginal zone lymphoma. Antibiotic therapy (analogous to Helicobacter pylori infection in gastric MALT lymphoma) might be helpful with the aim of averting or at least deferring the indication for more aggressive treatment.

A bactericidal monoclonal antibody elicits a change in its antigen, OspB of Borrelia burgdorferi, that can be detected by limited proteolysis

mAb CB2, directed against outer surface protein B (OspB), causes bacteriolysis of Borrelia burgdorferi in the absence of complement. How this happens is unknown. We examined the effect of mAb binding on OspB tertiary structure by using limited proteolysis to probe changes in protein conformation. Truncated OspB (tOspB) that lacked N-terminal lipid was cleaved by four enzymes: trypsin, endoproteinase Arg-C, endoproteinase Asp-N, and endoproteinase Glu-C. CB2 affected the cleavage by trypsin and Arg-C, but not by AspN or Glu-C. None of the enzymes cleaved CB2 under these conditions. Both trypsin and Arg-C cleaved tOspB near the N-terminus; CB2 slowed the rate of cleavage, but did not affect the identity of the sites cleaved. Irrelevant mAb had no effect, indicating that the effect was specific. CB2 was active against tOspB of strain B31, but not against tOspB of strain BEP4, to which it does not bind, suggesting that binding was required to elicit the effect on cleavage. With trypsin, CB2 showed a maximal effect at 8 mol of tOspB to 1 mol of mAb. At this ratio, not enough CB2 was present to bind all the tOspB; therefore, either CB2 shows turnover or CB2 acts by binding tOspB and effecting a change in this tOspB such that it, in turn, propagates the effect in other molecules of tOspB. Regardless of the mechanism, these data show that CB2 elicits a change in tOspB that can be measured by its reduced susceptibility to protease cleavage.

Lack of humoral immune protection against Treponema denticola virulence in a murine model

This study investigated the characteristics of humoral immune responses to Treponema denticola following primary infection, reinfection, and active immunization, as well as immune protection in mice. Primary infection with T. denticola induced a significant (400-fold) serum immunoglobulin G (IgG) response compared to that in control uninfected mice. The IgG response to reinfection was 20, 000-fold higher than that for control mice and 10-fold higher than that for primary infection. Mice actively immunized with formalin-killed treponemes developed serum antibody levels seven- to eightfold greater than those in animals after primary infection. Nevertheless, mice with this acquired antibody following primary infection or active immunization demonstrated no significant alterations of lesion induction or decreased size of the abscesses following a challenge infection. Mice with primary infection developed increased levels of IgG3, IgG2b, and IgG2a antibodies, with IgG1 being lower than the other subclasses. Reinfected mice developed enhanced IgG2b, IgG2a, and IgG3 and less IgG1. In contrast, immunized mice developed higher IgG1 and lower IgG3 antibody responses to infection. These IgG subclass distributions indicate a stimulation of both Th1 and Th2 activities in development of the humoral immune response to infection and immunization. Our findings also demonstrated a broad antigen reactivity of the serum antibody, which was significantly increased with reinfection and active immunization. Furthermore, serum antibody was effective in vitro in immobilizing and clumping the bacteria but did not inhibit growth or passively prevent the treponemal infection. These observations suggest that humoral immune responses, as manifested by antibody levels, isotype, and antigenic specificity, were not capable of resolving a T. denticola infection.

Dual role of interleukin-10 in murine Lyme disease: regulation of arthritis severity and host defense

In the murine model of Lyme disease, C3H/He mice exhibit severe arthritis while C57BL/6N mice exhibit mild lesions when infected with Borrelia burgdorferi. Joint tissues from these two strains of mice harbor similar concentrations of B. burgdorferi, suggesting that the difference in disease severity reflects differences in the magnitude of the inflammatory response to B. burgdorferi lipoproteins. Stimulation of bone marrow macrophages from C3H/HeN mice with the B. burgdorferi lipoprotein OspA resulted in higher-level production of the inflammatory mediators tumor necrosis factor alpha, nitric oxide, and interleukin-6 (IL-6) than that of macrophages from C57BL/6N mice. In contrast, macrophages from C57BL/6N mice consistently produced larger amounts of the anti-inflammatory cytokine IL-10 than did C3H/HeN macrophages. Addition of recombinant IL-10 suppressed the production of inflammatory mediators by macrophages from both strains. IL-10 was found to modulate B. burgdorferi-induced inflammation in vivo, since C57BL/6J mice deficient in IL-10 (IL-10-/-) developed more severe arthritis than wild-type C57BL/6J mice. The increase in arthritis severity was associated with a 10-fold decrease in the number of B. burgdorferi organisms present in ankle tissues from IL-10-/- mice. These findings suggest that in C57BL/6 mice, IL-10-dependent regulation of arthritis severity occurs at the expense of effective control of bacterial numbers.

Molecular genetics of extranodal marginal zone (MALT-type) B-cell lymphoma

Mucosa-associated lymphoid tissue lymphoma is now classified as extranodal marginal zone B-cell lymphoma. We reviewed the current literature on the biological and genetic mechanisms that lead to the development and progression of this unusual lymphoma. Particular attention was given to the clinical and biological significance of the immunoglobulin genes rearrangement, that has been proposed and widely used both diagnostically and as a tool to monitor the response to antibiotic treatment.

Detection of Borrelia burgdorferi sensu stricto by reverse line blot in the joints of Dutch patients with Lyme arthritis

OBJECTIVE

To analyze the presence of Borrelia burgdorferi sensu lato in synovial samples from the knee joint of patients with Lyme arthritis by polymerase chain reaction, and to differentiate the species by reverse line blot (RLB).

METHODS

Synovial fluid (SF) and synovial tissue (ST) samples were obtained from patients with Lyme arthritis (n = 4) and from patients with various other forms of arthritis (n = 9). DNA extracted from synovial samples was amplified by using, as a target, the spacer region between the 5S and 23S ribosomal RNA genes of B. burgdorferi sensu lato. Subsequently, 4 species-specific DNA probes were used in the RLB for specific hybridization.

RESULTS

DNA from B. burgdorferi sensu stricto DNA was detected in the SF and ST from 3 patients with Lyme arthritis. B. burgdorferi sensu lato DNA was not detected in the synovial samples from 9 control patients.

CONCLUSION

The relationship between different species of B. burgdorferi sensu lato and arthritis can be studied using direct analysis of extracted DNA from joint samples. This method can be used to study the association between particular clinical manifestations of Lyme disease and different species of B. burgdorferi sensu lato.

Quantitative detection of Borrelia burgdorferi by real-time PCR

Currently, no easy and reliable methods allowing for the quantification of Borrelia burgdorferi in tissues of infected humans or animals are available. Due to the lack of suitable assays to detect B. burgdorferi CFU and the qualitative nature of the currently performed PCR assays, we decided to exploit the recently developed real-time PCR. This technology measures the release of fluorescent oligonucleotides during the PCR. Flagellin of B. burgdorferi was chosen as the target sequence. A linear quantitative detection range of 5 logs with a calculated detection limit of one to three spirochetes per assay reaction mixture was observed. The fact that no signals were obtained with closely related organisms such as Borrelia hermsii argues for a high specificity of this newly developed method. A similar method was developed to quantify mouse actin genomic sequences to allow for the standardization of spirochete load. The specificity and sensitivity of the B. burgdorferi and the actin real-time PCR were not altered when samples were spiked with mouse cells or spirochetes, respectively. To evaluate the applicability of the real-time PCR, we used the mouse model of Lyme disease. The fate of B. burgdorferi was monitored in different tissues from inbred mice and from mice treated with antibiotics. Susceptible C3H/HeJ mice had markedly higher burdens of bacterial DNA than resistant BALB/c mice, and penicillin G treatment significantly reduced the numbers of spirochetes. Since these results show a close correlation between clinical symptoms and bacterial burden of tissues, we are currently analyzing human biopsy specimens to evaluate the real-time PCR in a diagnostic setting.

Protection from Lyme neuroborreliosis in nonhuman primates with a multiantigenic vaccine

In an effort to develop an effective and safe vaccine for lyme disease, rhesus macaques were injected with a multiantigenic preparation of Borrelia burgdorferi, strain N40. One month later animals were boosted before intradermal challenge with infectious B. burgdorferi. Challenges were performed at 1 and again at 5 months after the booster vaccination. Vaccinated and control nonvaccinated animals were monitored for development of systemic infection by measurement of serum anti-spirochetal antibodies by ELISA and Western blotting, and neurological involvement was monitored by testing of cerebrospinal fluid (CSF) and PCR analysis of central nervous system (CNS) tissue obtained at necropsy. Two control nonhuman primates (NHPs), given saline injections instead of vaccine and then challenged with B. burgdorferi, developed CSF pleocytosis, PCR positivity of the brain, and high levels of specific anti-B. burgdorferi antibody in the serum and CSF. Necropsy studies revealed widespread invasion of the CNS of one of these animals by the spirochete. In contrast, none of the four vaccinated animals developed evidence of invasion of the CNS after either of two challenge inoculations with infectious B. burgdorferi. In addition to resisting infection, no vaccinated animal demonstrated any untoward consequence of vaccination. These data demonstrate that a multiantigenic vaccine is effective in preventing systemic infection and lyme neuroboreliosis in NHPs and suggest that a successful vaccine could be developed in humans which would prevent lyme disease.

Soluble proteins isolated from Borrelia burgdorferi by extraction with Triton X-114 confer resistance to experimental infection

Fractionation of Borrelia burgdorferi was made by extraction of infectious spirochetes using the detergent Triton X-114. Gel electrophoresis analysis of hydrophilic and hydrophobic proteins demonstrated that detergent extraction resulted in two populations of proteins with nonoverlapping electrophoretic profiles. Immunoblot analysis with monoclonal antibodies reactive with two abundant membrane proteins demonstrated that hydrophilic proteins were uncontaminated with hydrophobic proteins. In addition, assay of thymidine incorporation into and secretion of tumor necrosis factor-alpha from splenocytes cocultured in vitro with either detergent or aqueous phase proteins showed that lymphocyte mitogenic and macrophage activation activities of B. burgdorferi were completely absent from the hydrophilic phase proteins. The Triton X-114 aqueous and detergent phase proteins were used to immunize BALB/c and separately microMT/microMT (B cell knockout) mice that were subsequently challenged with infectious B. burgdorferi. The hydrophilic phase proteins were able to induce protective resistance to infection in either strain of mice demonstrating that potential candidate vaccine antigens are contained in the biochemical class of antigens which is devoid of both lymphocyte mitogen activity and major outer surface proteins. Furthermore, the ability to vaccinate B cell knockout mice suggests that the humoral antispirochete immune response is not the exclusive basis for protective immunity.

Kinetics and in vivo induction of genetic variation of vlsE in Borrelia burgdorferi

The Lyme disease agent, Borrelia burgdorferi, is able to persistently infect humans and animals for months or years in the presence of an active immune response. It is not known how the organisms survive immune attack in the mammalian host. vlsE, a gene localized near one end of linear plasmid lp28-1 and encoding a surface-exposed lipoprotein in B. burgdorferi B31, was shown recently to undergo extensive genetic and antigenic variation within 28 days of initial infection in C3H/HeN mice. In this study, we examined the kinetics of vlsE sequence variation in C3H/HeN mice at 4, 7, 14, 21, and 28 days and at 7 and 12 months postinfection. Sequence changes were detected by PCR amplification and sequence analysis as early as 4 days postinfection and accumulated progressively in both C3H/HeN and CB-17 severe combined immunodeficient (SCID) mice throughout the course of infection. The sequence changes were consistent with sequential recombination of segments from multiple silent vls cassette sites into the vlsE expression site. No vlsE sequence changes were detected in organisms cultured in vitro for up to 84 days. These results indicate that vlsE recombination is induced by a factor(s) present in the mammalian host, independent of adaptive immune responses. The possible inducing conditions appear to be present in various tissue sites because isolates from multiple tissues showed similar degrees of sequence variation. The rate of accumulation of predicted amino acid changes was higher in the immunologically intact C3H/HeN mice than in SCID mice, a finding consistent with immune selection of VlsE variants.

The Role of CD14 in Signaling Mediated by Outer Membrane Lipoproteins of Borrelia burgdorferi

Borrelia burgdorferi possesses membrane lipoproteins that exhibit stimulatory properties and, consequently, have been implicated in the pathology related to Lyme disease. As CD14 has been shown to mediate signaling by a number of lipid-modified bacterial products, the involvement of CD14 in signaling mediated by two B. burgdorferi lipoproteins, outer surface protein A (OspA) and OspC, was determined. Lipoprotein-mediated induction of nuclear factor-κB nuclear translocation and production of IL-8 and IL-6 in HUVEC was enhanced in the presence of serum or soluble rCD14. CD14-specific Abs that block LPS-mediated signaling also inhibited lipoprotein-dependent signaling in HUVEC and neutrophils. The formation of stable complexes between OspA and CD14 was demonstrated by native gel electrophoresis. LPS was found to compete with OspA for binding with CD14, suggesting that LPS and OspA bind similar regions on CD14. The similarity in binding was further supported by the finding that a mutant soluble CD14, lacking the LPS binding site, did not facilitate lipoprotein signaling, nor did it form a complex with OspA. Binding of OspA to CD14 was dependent on the lipid modification, as unlipidated OspA did not form a complex with CD14 or stimulate cells. In contrast, the lipopeptide remaining after proteinase K digestion both formed a complex with CD14 and retained stimulatory properties. These findings indicate that CD14 facilitates bacterial lipoprotein signaling in mammalian cells.

CD40 and CD154 in cell-mediated immunity

CD40-CD154-mediated contact-dependent signals between B and T cells are required for the generation of thymus dependent (TD) humoral immune responses. CD40-CD154 interactions are however also important in many other cell systems. CD40 is expressed by a large variety of cell types other than B cells, and these include dendritic cells, follicular dendritic cells, monocytes, macrophages, mast cells, fibroblasts, and endothelial cells. CD40- and CD154-knockout mice and antibodies to CD40 and CD154 have helped to elucidate the role of the CD40-CD154 system in immune responses. Recently published studies indicate that CD40-CD154 interactions can influence T cell priming and T cell-mediated effector functions; they can also upregulate costimulatory molecules and activate macrophages, NK cells, and endothelia as well as participate in organ-specific autoimmune disease, graft rejection, and even atherosclerosis. This review focuses on the role of the CD40-CD154 system in the regulation of many newly discovered functions important in inflammation and cell-mediated immunity.

Identification of a T Cell Subset Capable of both IFN-γ and IL-10 Secretion in Patients with Chronic Borrelia burgdorferi Infection

A novel population of both IFN-γ- and IL-10-secreting human T cells that differentiate in the presence of exogenous IL-12 in vitro has recently been described. Whether this T cell population exists in vivo is unknown. Borrelia burgdorferi, the etiologic agent of Lyme disease, can induce a chronic infection in the presence of a vigorous humoral immune response. We established T cell lines specific for B. burgdorferi and tetanus toxoid from subjects with chronic B. burgdorferi infection and healthy controls in limiting dilution experiments and assessed proliferation and cytokine secretion. As expected, higher frequencies of B. burgdorferi-specific precursor T cells were observed in Lyme patients compared with controls. In both groups of subjects, T cell lines specific for B. burgdorferi secreted high amounts of IFN-γ. However, in patients with Lyme disease, 27% of T cell lines secreted not only IFN-γ but also IL-10, which was only observed in 0.6% of B. burgdorferi-reactive T cell lines generated from controls and in none of the tetanus toxoid-reactive T cell lines generated from either Lyme patients and controls. Single cell PHA cloning confirmed that both cytokines were secreted from one clonally expanded precursor cell. Whole mononuclear cells from B. burgdorferi-infected individuals, but not from controls, secreted IL-12. Moreover, neutralizing anti-IL-12 mAbs inhibited the generation of the IFN-γ/IL-10 population. These data demonstrate that this novel population of IL-12-induced IFN-γ/IL-10-secreting T cells is generated in response to chronic B. burgdorferi infection.

Therapeutic passive vaccination against chronic Lyme disease in mice

Passive and active immunization against outer surface protein A (OspA) has been successful in protecting laboratory animals against subsequent infection with Borrelia burgdorferi. Antibodies (Abs) to OspA convey full protection, but only when they are present at the time of infection. Abs inactivate spirochetes within the tick and block their transmission to mammals, but do not affect established infection because of the loss of OspA in the vertebrate host. Our initial finding that the presence of high serum titers of anti-OspC Abs (5 to 10 microg/ml) correlates with spontaneous resolution of disease and infection in experimentally challenged immunocompetent mice suggested that therapeutic vaccination with OspC may be feasible. We now show that polyclonal and monospecific mouse immune sera to recombinant OspC, but not to OspA, of B. burgdorferi resolve chronic arthritis and carditis and clear disseminated spirochetes in experimentally infected C.B.-17 severe combined immunodeficient mice in a dose-dependent manner. This was verified by macroscopical and microscopical examination of affected tissues and recultivation of spirochetes from ear biopsies. Complete resolution of disease and infection was achieved, independent of whether OspC-specific immune sera (10 microg OspC-specific Abs) were repeatedly given (4x in 3- to 4-day intervals) before the onset (day 10 postinfection) or at the time of fully established arthritis and carditis (days 19 or 60 postinfection). The results indicate that in mice spirochetes constitutively express OspC and are readily susceptible to protective OspC-specific Abs throughout the infection. Thus, an OspC-based vaccine appears to be a candidate for therapy of Lyme disease.

Interleukin-12 in infectious diseases

Interleukin-12 (IL-12) is a potent immunoregulatory cytokine that is crucially involved in a wide range of infectious diseases. In several experimental models of bacterial, parasitic, viral, and fungal infection, endogenous IL-12 is required for early control of infection and for generation and perhaps maintenance of acquired protective immunity, directed by T helper type 1 (Th1) cells and mediated by phagocytes. Although the relative roles of IL-12 and gamma interferon in Th1-cell priming may be to a significant extent pathogen dependent, common to most infections is that IL-12 regulates the magnitude of the gamma interferon response at the initiation of infection, thus potentiating natural resistance, favoring Th1-cell development; and inhibiting Th2 responses. Treatment of animals with IL-12, either alone or as a vaccine adjuvant, has been shown to prevent disease by many of the same infectious agents, by stimulating innate resistance or promoting specific reactivity. Although IL-12 may enhance protective memory responses in vaccination or in combination with antimicrobial chemotherapy, it is yet unclear whether exogenous IL-12 can alter established responses in humans. Continued investigation into the possible application of IL-12 therapy to human infections is warranted by the role of the cytokine in inflammation, immunopathology, and autoimmunity.

Ablation of interleukin-12 exacerbates Lyme arthritis in SCID mice

The administration of interleukin-12 (IL-12) antibodies to Borrelia burgdorferi-infected C3H/HeN-scid mice increased the severity of acute Lyme arthritis. These results contrasted with the reduction of Lyme arthritis by IL-12 antibodies in immunocompetent animals. These data suggest that downregulation of innate immunity in SCID mice in the absence of B- and T-cell responses leads to an exacerbation of joint inflammation.

The CD40-CD154 system in anti-infective host defense

Research in the past few years has documented significant advances in our understanding of the CD40-CD40 ligand (CD154) system in diverse immune functions. This system influences many T cell mediated inflammatory immune responses and effector functions, unmasking a previously unexpected role for CD40-CD154 in cell mediated immunity. Manipulation of CD154 in animal models of infection by the use of CD154-deficient mice or anti-CD154 antibodies has shown the importance of this system in the initiation of the inflammatory response, in the activation of antigen-presenting cells and in resistance to infections.