Evidence for (lipo) oligosaccharides in Borrelia burgdorferi and their serological specificity

Inflammatory mediator release from primary rhesus microglia in response to Borrelia burgdorferi results from the activation of several receptors and pathways

BACKGROUND

In previous studies, neurons were documented to undergo apoptosis in the presence of microglia and live Borrelia burgdorferi, but not with either agent alone. Microscopy showed that several Toll-like receptors (TLRs) were upregulated in microglia upon B. burgdorferi exposure. It was hypothesized that the inflammatory milieu generated by microglia in the presence of B. burgdorferi results in neuronal apoptosis and that this inflammation was likely generated through TLR pathways.

METHODS

In this study, we explored the role of several TLR and nucleotide-binding oligomerization domain containing 2 (NOD2)-dependent pathways in inducing inflammation in the presence of B. burgdorferi, using ribonucleic acid interference (RNAi) and/or inhibitors, in primary non-human primate (NHP) microglia. We also used several inhibitors for key mitogen-activated protein kinase (MAPK) pathways to determine the role of downstream pathways in inflammatory mediator release.

RESULTS

The results show that the TLR2 pathway plays a predominant role in inducing inflammation, as inhibition of TLR2 with either small interfering RNA (siRNA) or inhibitor, in the presence of B. burgdorferi, significantly downregulated interleukin 6 (IL-6), chemokine (C-X-C) motif ligand 8 (CXCL8), chemokine (C-C) motif ligand 2 (CCL2), and tumor necrosis factor (TNF) production. This was followed by TLR5, the silencing of which significantly downregulated IL-6 and TNF. The role of TLR4 was inconclusive as a TLR4-specific inhibitor and TLR4 siRNA had opposing effects in the presence of B. burgdorferi. Silencing of NOD2 by siRNA in the presence of B. burgdorferi significantly upregulated IL-6, CCL2, and TNF. Downstream signaling involved the adaptor molecule myeloid differentiation primary response 88 (MyD88), as expected, as well as the MAPK pathways, with extracellular signal-regulated kinase (ERK) being predominant, followed by Jun N-terminal kinase (JNK) and p38 pathways.

CONCLUSIONS

Several receptors and pathways, with both positive and negative effects, mediate inflammation of primary microglia in response to B. burgdorferi, resulting in a complex, tightly regulated immune network.

Synthesis and antigenicity of BBGL-2 glycolipids of Borrelia burgdorferi, the causative agent of Lyme disease

Borrelia burgdorferi is the etiological agent for Lyme disease (LD), the most common vector borne disease in the United States. There is no human vaccine against LD currently available. Our approach to a vaccine is based on its surface-exposed glycolipids. One group of these glycolipids termed BBGL-2 consists of 1,2-di-O-acyl-3-O-(α-d-galactopyranosyl)-sn-glycerol congeners having palmitic, oleic, stearic, linoleic, and myristic acids. In order to delineate the immunodominant region(s) of the BBGL-2 components, we embarked on a synthetic project to provide available structurally defined, homogeneous analogs of BBGL-2 that might help identify the best vaccine candidate. The antigenicity of the synthetic glycolipids was examined by dot-blot analysis using mice sera obtained by immunization with killed B. burgdorferi cells, with native BBGL-2 in complete Freund's adjuvant, as well as sera obtained from patients with Lyme disease. We found that the presence of two acyl groups in the glycerol moiety was essential for antigenicity. At least one of these groups must be an oleoyl moiety. Neither the anomeric configuration of the galactose nor the configuration of the glycerol at C-2 was a decisive factor. Based on these findings we designed an 'unnatural' BBGL-2 analog having the structure 3-O-(β-d-galactopyranosyl)-1,2-di-O-oleoyl-dl-glycerol which is easier and less expensive to synthesize than the other BBGL-2 congeners prepared in this study. This substance proved to be antigenic and is considered a candidate vaccine for Lyme disease.

Natural killer T cells recognize diacylglycerol antigens from pathogenic bacteria

Natural killer T (NKT) cells recognize glycosphingolipids presented by CD1d molecules and have been linked to defense against microbial infections. Previously defined foreign glycosphingolipids recognized by NKT cells are uniquely found in nonpathogenic sphingomonas bacteria. Here we show that mouse and human NKT cells also recognized glycolipids, specifically a diacylglycerol, from Borrelia burgdorferi, which causes Lyme disease. The B. burgdorferi-derived, glycolipid-induced NKT cell proliferation and cytokine production and the antigenic potency of this glycolipid was dependent on acyl chain length and saturation. These data indicate that NKT cells recognize categories of glycolipids beyond those in sphingomonas and suggest that NKT cell responses driven by T cell receptor-mediated glycolipid recognition may provide protection against diverse pathogens.

A newly discovered cholesteryl galactoside from Borrelia burgdorferi

Two major glycolipids, which comprise approximately 36% of the total lipid mass from Borrelia burgdorferi, the etiological agent of Lyme disease, were investigated. We determined the fatty acid type, sugar identity, anomeric configuration, and substituent type and position. The structures were identified as cholesteryl 6-O-acyl-beta-d-galactopyranoside (B. burgdorferi glycolipid 1, BbGL-I), and 1,2-di-O-acyl-3-O-alpha-d-galactopyranosyl-sn-glycerol (BbGL-II). The major fatty acids were palmitate and oleate. The structures were corroborated by gas-liquid chromatography MS, matrix-assisted laser desorption/ionization time-of-flight spectroscopy, fast atom bombardment MS, detailed NMR spectrometry, and metabolic labeling. This is a previously undescribed demonstration of a cholesteryl galactoside in bacteria. Lipopolysaccharide was not detected in B. burgdorferi. The two glycolipids have several properties suggesting they may function as lipopolysaccharide: both are main components of the bacterial membrane, surface exposed, and have a three-domain structure. BbGL-I elicited specific antibodies in mice and rabbits, and BbGL-II elicited antibodies that reacted with both glycolipids.

Borrelia burgdorferi RevA antigen is a surface-exposed outer membrane protein whose expression is regulated in response to environmental temperature and pH

Borrelia burgdorferi, the causative agent of Lyme disease, produces RevA protein during the early stages of mammalian infection. B. burgdorferi apparently uses temperature as a cue to its location, producing proteins required for infection of warm-blooded animals at temperatures corresponding to host body temperature, but does not produce such virulence factors at cooler, ambient temperatures. We have observed that B. burgdorferi regulates expression of RevA in response to temperature, with the protein being synthesized by bacteria cultivated at 34 degrees C but not by those grown at 23 degrees C. Tissues encountered by B. burgdorferi during its infectious cycle vary in their pH values, and the level of RevA expression was also found to be dependent upon pH of the culture medium. The cellular localization of RevA was also analyzed. Borrelial inner and outer membranes were purified by isopycnic centrifugation, and membrane fractions were conclusively identified by immunoblot analysis using antibodies raised against the integral inner membrane protein MotB and outer membrane-associated Erp lipoproteins. Immunoblot analyses indicated that RevA is located in the B. burgdorferi outer membrane. These analyses also demonstrated that an earlier report (H. A. Bledsoe et al., Infect. Immun. 176:7447-7455, 1994) had misidentified such B. burgdorferi membrane fractions. RevA was further demonstrated to be exposed to the external environment, where it could facilitate interactions with host tissues.

Structural analysis of glycolipids from Borrelia burgdorferi

In this study the lipids of Borrelia burgdorferi, the causative agent of Lyme disease, were analyzed. Lipids comprise about 25-30% of the cell dry weight. The lipid fraction could be separated by HPTLC into 11 components. Staining of these components revealed two glycolipids and two phospholipids. The glycolipids represented about 50% of the total lipids and comprised only galactose as monosaccharide constituents. By means of mass spectrometric and gas chromatographic analysis both glycolipids could be identified as alpha-galactosyl-diacylglycerolipids with different fatty acid compositions. The phospholipids were identified as phosphatidylcholine and phosphatidylglycerol. Immunoassays with sera from patients with Lyme disease showed antibody reactivity only to the glycolipids, which was present in all stages of the disease. Other lipid components seemed to be non-immunogenic in Lyme disease. The glycolipids of B. burgdorferi may be, thus, considered promising candidates for diagnosis and possibly also for vaccination.

Surface exposure and protease insensitivity of Borrelia burgdorferi Erp (OspEF-related) lipoproteins

Borrelia burgdorferi can encode numerous lipoproteins of the Erp family. Although initially described as outer surface proteins, the technique used in that earlier study has since been demonstrated to disrupt bacterial membranes and allow labelling of subsurface proteins. Data are now presented from additional analyses indicating that Erp proteins are indeed surface exposed in the outer membrane. Surface localization of these infection-associated proteins indicates the potential for interactions of Erp proteins with vertebrate tissues. Some Erp proteins were resistant to in situ digestion by certain proteases, suggesting that those proteins fold in manners which hide protease cleavage sites, or that they interact with other protective membrane components. Additionally, cultivation of B. burgdorferi in the presence of antibodies directed against Erp proteins inhibited bacterial growth.

Evidence for a new type of outer membrane lipid in oral spirochete Treponema denticola. Functioning permeation barrier without lipopolysaccharides

A new class of outer membrane lipid (OML) was isolated from the oral spirochete Treponema denticola strain ATCC 33521 using a phenol/chloroform/light petroleum procedure normally applied for lipopolysaccharide extraction. In addition to chemical analysis, Fourier transform infrared (FTIR) spectroscopy was applied to compare the biophysical properties of OML with lipopolysaccharides (LPS) and lipoteichoic acids (LTA). Isolated OML fractions represent 1.4% of the total dry cell weight, are about 4 kDa in size, and contain 6% amino sugars, 8% neutral sugars, 14% phosphate, 35% carbazol-positive compounds, and 11% fatty acids (containing iso- and anteiso-fatty acyl chains). Rare for outer membrane lipids, OML contains no significant amount of 3-deoxy-D-manno-octulosonic acids, heptoses, and beta-hydroxy fatty acids. The fatty acyl chain composition, being similar to that of the cytoplasmic membrane, is quite heterogeneous with anteiso-pentadecanoic acid (12%), palmitic acid (51%), and iso-palmitic acid (19%) as the predominant fatty acids present. Findings of a glycerol-hexose unit and two glycerol-hexadecanoic acid fragments indicate a glycolipid membrane anchor typically found in LTA. There was also no evidence for the presence of a sphingosine-based lipid structure. The results of FTIR measurements strongly suggest that the reconstituted lipid forms normal bilayer structures (vesicles) expressing a high membrane state of order with a distinct phase transition as typical for isolated LPS. However, in contrast to LPS, OML of T. denticola has a lower Tm near 22 degreesC and a lower cooperativity of the phase transition. The results suggest a different kind of permeation barrier that is built up by this particular OML of T. denticola, which is quite different from LPS normally essential for Gram-negative bacteria.

Relationship between the Borrelia burgdorferi specific immune response and different stages and syndromes in neuroborreliosis

One hundred untreated neuroborreliosis patients were investigated by IgG/IgM immunoblot to find out if different stages and syndromes are characterized by different patterns of their Borrelia burgdorferi specific immune responses in CSF and serum. Stage III (n = 10) was characterized by a broad, highly specific intrathecal immune response (the mean number of IgM bands in CSF was 3.1 and of IgG bands 6.3). All patients recognized one or more of the following proteins (p35, p21, p18) or the 5 kd glycolipid. In contrast, the immune response in stage II (n = 90) was less restricted (28%) and heterogeneous (mean number of IgM bands 1.4 and of IgG bands 3.4). It was mainly directed against the highly crossreactive p41 antigen (91%). The different clinical features of stage II were comparable regarding the intrathecal immune response. However anti-glycolipid and anti-p35, -p21, -p18 IgG antibodies were detected in a small subset of patients, mainly corresponding to more severe courses of the disease. Our data are compatible with a direct agent-related pathomechanism in neuroborreliosis. Antibodies against certain proteins and the glycolipid of B. burgdorferi seem to have a prognostic value as to the development of more severe disease or transition to stage III.

IgM and IgG significant reactivity to Borrelia burgdorferi sensu stricto, Borrelia garinii and Borrelia afzelii among Italian patients affected by Lyme arthritis or neuroborreliosis

This survey evaluates the specificity of band patterns in immunoblot of sera taken from clinically defined cases of Lyme arthritis and neuroborreliosis, towards three locally isolated strains of Borrelia burgdorferi, belonging to the three species: Borrelia sensu stricto, Borrelia garinii and Borrelia afzelii. To assess specificity, patient sera were statistically (X2, P < or = 0.05) compared with blood donors sera samples. Both IgG and IgM antibodies were considered. The overall reactivity of the three Borrelia strains in IgG immunoblots indicated that ten protein bands were significant, with a different prevalence of some of them in the two groups of patient sera: bands at 60-58, 30-33, 36-37 and 28-27 kDa were markers for neuroborreliosis sera; proteins at 100-83, 72-70 and 18-17 kDa behaved like markers for Lyme arthritis. The IgM Immunoblots revealed significant bands at 100-83, 72-70, 51, 24-21 and 18-17 kDa only with neuroborreliosis sera. Though there were variable band reactivities in each strain, a correlation emerged between the three genospecies and the clinical symptoms: in fact B. afzelii and B. garinii were prevalent in Lyme arthritis sera, (IgG Immunoblots); B. garinii was associated to neuroborreliosis (IgG and IgM Immunoblots); B. sensu stricto was strongly reactive with neuroborreliosis in IgM immunoblots. These data indicate that the three locally strains of Borrelia representing the three genospecies should be used together in immunoblot to detect antibodies elicited in neuroborreliosis and Lyme arthritis.

Prevalence of antibodies against Borrelia species in patients with unclassified uveitis in regions in which Lyme disease is endemic and nonendemic

We studied 93 patients with unclassified uveitis from two regions in Japan (Hokkaido and Kanagawa) to assess the contribution of Borrelia species to this condition. The seroprevalence of antibody to Borrelia species was higher in patients from Hokkaido than in those from Kanagawa. The unclassified uveitis of seropositive patients was probably a complication of Lyme borreliosis since (i) the antibody titers were as high as those in clinically diagnosed Lyme disease patients, (ii) healthy controls from Hokkaido showed low seroprevalence in contrast with unclassified uveitis patients from Hokkaido, and (iii) the reaction pattern of antibodies in sera from patients with unclassified uveitis was the same as that in patients with Lyme disease. This is the first report to reveal the high risk of Lyme borreliosis in patients with unclassified uveitis in regions endemic for Lyme disease. In case of unclassified uveitis as well as in cases of inflammatory disease of unknown origin, Lyme disease should be taken into consideration, especially in regions in which Lyme diseases is endemic, even if it is reported only in animals.

Serological distinction between syphilis and Lyme borreliosis

The serological distinction of an immune response to the agent of syphilis, Treponema (T.) pallidum, and Lyme disease borreliae is difficult due to the existence of cross-reacting antibodies. In this study, the immunoblot technique is used to compare the immune response of sera from patients with syphilis or Lyme borreliosis to either T. pallidum or Borrelia (B.) burgdorferi. Patients with syphilis showed an IgG response to the 17 and 15 kDa antigens of T. pallidum, whereas sera from patients with Lyme borreliosis-especially in late stages of the disease-reacted with the 95 and 19-17 kDa antigens of B. burgdorferi. Thus, IgG antibodies against low molecular weight antigens of T. pallidum (17, 15 kDa) or B. burgdorferi (19-17 kDa) may represent useful markers for the serological diagnosis of syphilis or Lyme borreliosis.

Purification and immunological characterization of a major low-molecular-weight lipoprotein from Borrelia burgdorferi

Borrelia burgdorferi resembles gram-negative bacteria in having both cellular and outer membranes. We previously showed that a lipopolysaccharide (LPS)-like material could be extracted from B. burgdorferi with phenol-chloroform-petroleum ether (PCP). The PCP extract of B. burgdorferi exhibited biological activity in several in vitro assays (e.g., mitogenicity, pyrogenicity, and cytokine release). These activities suggested the presence of endotoxin. The PCP extract of B. burgdorferi, however, also contained a small amount of protein. Preliminary studies showed that monoclonal antibody prepared against this protein inhibited the mitogenic activity of the PCP extract toward murine spleen cells. The current study was therefore undertaken to characterize this protein and to establish methods for its separation from the LPS. The PCP-extracted protein consisted of a single, low-molecular-weight lipoprotein (apparent M(r), 10,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) (SDS-PAGE). By protein analysis, it accounted for 2% of the dry weight of defatted cells, thus making it a major constituent of the spirochete. It was purified from the LPS by initial extraction into 10% Triton X-100 followed by immunoaffinity chromatography in the presence of detergent. On removal of the LPS, the purified lipoprotein formed aggregates stable to SDS-PAGE which were detectable on Western blots (immunoblots) probed with either the monoclonal antibody or polyclonal antiserum. From a plot of the aggregate molecular weight versus aggregate size, a monomer molecular weight of 7,500 was obtained. Indirect immunofluorescence with the monoclonal antibody showed that the lipoprotein was exposed at the surface of the spirochete in only a small percentage of cells. The lipoprotein was present in several strains of B. burgdorferi but absent in other Borrelia spp., treponemes, and gram-negative human pathogens, indicating species specificity.

Immunodominant antigens recognized by the human immune response to infection by organisms of the species Leptospira interrogans serogroup Australis

Serum samples from patients infected by organisms of Leptospira interrogans serogroup Australis were tested by Western blot to determine the nature of major antigens that are involved in the immune response. Although there was some patient-to-patient variability, immunodominant genus-specific antigens were found to be proteins of apparent molecular ratio 68, 46 and 35-kDa, and lipopolysaccharide (LPS) sub-units in the 35-14-kDa region. Serogroup epitopes specific for Australis were exclusively saccharides of about 32 and 24 kDa: a serovar-specific antigen for serovar lora was of 38-40 kDa and behaved like a protein. Antibodies to the LPS serogroup-specific antigens and to the 38-40 kDa protein were long-lasting and consequently suggest that these immunodominant epitopes are important in resistance to re-infection.