Adhesion of Borrelia garinii to neuronal cells is mediated by the interaction of OspA with proteoglycans

Distinctive Evasion Mechanisms to Allow Persistence of Borrelia burgdorferi in Different Human Cell Lines

Lyme borreliosis is a multisystemic disease caused by the pleomorphic bacteria of the Borrelia burgdorferi sensu lato complex. The exact mechanisms for the infection to progress into a prolonged sequelae of the disease are currently unknown, although immune evasion and persistence of the bacteria in the host are thought to be major contributors. The current study investigated B. burgdorferi infection processes in two human cell lines, both non-immune and non-phagocytic, to further understand the mechanisms of infection of this bacterium. By utilizing light, confocal, helium ion, and transmission electron microscopy, borrelial infection of chondrosarcoma (SW1353) and dermal fibroblast (BJ) cells were examined from an early 30-min time point to a late 9-days post-infection. Host cell invasion, viability of both the host and B. burgdorferi, as well as, co-localization with lysosomes and the presence of different borrelial pleomorphic forms were analyzed. The results demonstrated differences of infection between the cell lines starting from early entry as B. burgdorferi invaded BJ cells in coiled forms with less pronounced host cell extensions, whereas in SW1353 cells, micropodial interactions with spirochetes were always seen. Moreover, infection of BJ cells increased in a dose dependent manner throughout the examined 9 days, while the percentage of infection, although dose dependent, decreased in SW1353 cells after reaching a peak at 48 h. Furthermore, blebs, round body and damaged B. burgdorferi forms, were mostly observed from the infected SW1353 cells, while spirochetes dominated in BJ cells. Both infected host cell lines grew and remained viable after 9 day post-infection. Although damaged forms were noticed in both cell lines, co-localization with lysosomes was low in both cell lines, especially in BJ cells. The invasion of non-phagocytic cells and the lack of cytopathic effects onto the host cells by B. burgdorferi indicated one mechanism of immune evasion for the bacteria. The differences in attachment, pleomorphic form expressions, and the lack of lysosomal involvement between the infected host cells likely explain the ability of a bacterium to adapt to different environments, as well as, a strategy for persistence inside a host.

Crossing the Blood-Brain Barrier by Neuroinvasive Pathogens

The penetration of the blood-brain barrier (BBB) and invasion of the central nervous system (CNS) are important steps for all neuroinvasive pathogens. All of the ways of pathogens passing through the BBB are still unclear. Among known pathways, pathogen traversal can occur paracellularly, transcellularly or using a “Trojan horse” mechanism. The first step of translocation across the BBB is the interactions of the pathogen’s ligands with the receptors of the host brain cells. Lyme disease, the most common vector-borne disease in the temperate zones of Europe and North America, are caused by Borreliella species (former Borrelia burgdorferi sensu lato) that affects the peripheral and the CNS. In this review, we have presented various pathogen interactions with endothelial cells, which allow the disruption of the BBB so that the pathogens can pass across the BBB.

Deciphering the interface between a CD40 receptor and borrelial ligand OspA

Neuroborreliosis is serious sequelae of Lyme borreliosis. Neuroinvasion is largely relied on successful translocation of Borrelia across the blood-brain barrier. Adherence of Borrelia to brain microvascular endothelial cell (BMEC) seems to be critical for translocation. Here we unfold the interface between OspA and CD40 molecules, major ligand and receptor, that are involved in adhesion of Borrelia to BMECs. We found that a region between Asn127 and Asp205 of OspA forms the CD40-receptor binding site. This region encompasses human umbilical vein endothelial cell (HUVEC) binding domain and contains a potential ligand-binding pocket lined by three amino acid residues: Arg139, Glu160 and Lys189. Disruption of this pocket (by truncation of the HUVEC binding domain) caused complete abrogation of its ability to bind CD40. To identify the amino acid residues within the HUVEC binding domain involved in the CD40 binding, site-directed mutagenesis and binding assays were performed. Results showed that Asp149, Phe165, Ala172, Val186 and Leu192 might form interface with CD40 molecule. Other side of the interface was also identified with the help of a ligand-binding assay with OspA and truncated CD40 fragments. Results exposed that cysteine rich domain 2 (CRD2) of CD40 might be the site for OspA binding. Precise knowledge of the molecular basis of the ligand-receptor interactions is essential in order to understand mechanisms of pathogenesis and could help in the development of novel therapeutics and vaccines.

An insight into the ligand-receptor interactions involved in the translocation of pathogens across blood-brain barrier

Traversal of pathogen across the blood-brain barrier (BBB) is an essential step for central nervous system (CNS) invasion. Pathogen traversal can occur paracellularly, transcellularly, and/or in infected phagocytes (Trojan horse mechanism). To trigger the translocation processes, mainly through paracellular and transcellular ways, interactions between protein molecules of pathogen and BBB are inevitable. Simply, it takes two to tango: both host receptors and pathogen ligands. Underlying molecular basis of BBB translocation of various pathogens has been revealed in the last decade, and a plethora of experimental data on protein-protein interactions has been created. This review compiles these data and should give insights into the ligand-receptor interactions that occur during BBB translocation. Further, it sheds light on cell signaling events triggered in response to ligand-receptor interaction. Understanding of the molecular principles of pathogen-host interactions that are involved in traversal of the BBB should contribute to develop new vaccine and drug strategies to prevent CNS infections.

OspA-CD40 dyad: ligand-receptor interaction in the translocation of neuroinvasive Borrelia across the blood-brain barrier

Lyme borreliosis is the most widespread vector-borne disease in temperate zones of Europe and North America. Although the infection is treatable, the symptoms are often overlooked resulting in infection of the neuronal system. In this work we uncover the underlying molecular mechanism of borrelial translocation across the blood-brain barrier (BBB). We demonstrate that neuroinvasive strain of Borrelia readily crosses monolayer of brain-microvascular endothelial cells (BMECs) in vitro and BBB in vivo. Using protein-protein interaction assays we found that CD40 of BMECs and OspA of Borrelia are the primary molecules in transient tethering of Borrelia to endothelium. OspA of neuroinvasive Borrelia, but not of non-neuroinvasive strain, binds CD40. Furthermore, only the neuroinvasive Borrelia and its recombinant OspA activated CD40-dependent pathway in BMECs and induced expression of integrins essential for stationary adhesion. Demonstration of the CD40-ligand interactions may provide a new possible perspective on molecular mechanisms of borrelial BBB translocation process.

Analysis of Borrelia burgdorferi Surface Proteins as Determinants in Establishing Host Cell Interactions

Borrelia burgdorferi infection causes Lyme borreliosis in humans, a condition which can involve a systemic spread of the organism to colonize various tissues and organs. If the infection is left untreated by antimicrobials, it can lead to manifestations including, arthritis, carditis, and/or neurological problems. Identification and characterization of B. burgdorferi outer membrane proteins that facilitate cellular attachment and invasion to establish infection continue to be investigated. In this study, we sought to further define putative cell binding properties of surface-exposed B. burgdorferi proteins by observing whether cellular adherence could be blocked by antibodies. B. burgdorferi mixed separately with monoclonal antibodies (mAbs) against outer surface protein (Osp) A, OspC, decorin-binding protein (Dbp) A, BBA64, and RevA antigens were incubated with human umbilical vein endothelial cells (HUVEC) and human neuroglial cells (H4). B. burgdorferi treated with anti-OspA, -DbpA, and -BBA64 mAbs showed a significant decrease in cellular association compared to controls, whereas B. burgdorferi treated with anti-OspC and anti-RevA showed no reduction in cellular attachment. Additionally, temporal transcriptional analyses revealed upregulated expression of bba64, ospA, and dbpA during coincubation with cells. Together, the data provide evidence that OspA, DbpA, and BBA64 function in host cell adherence and infection mechanisms.

Neuroborreliosis: pathogenesis, symptoms, diagnosis and treatment

Lyme disease is the most common human tick-borne disease in the northern hemisphere. This article describes the current knowledge of several aspects of Lyme neuroborreliosis. The epidemiology is reviewed first, with special respect to the difference between European and American disease. Then, the current knowledge about the pathogenesis of Lyme neuroborreliosis is presented, with emphasis on immune evasion strategies. Furthermore, the clinical picture of acute Lyme neuroborreliosis and the frequently discussed post-Lyme disease syndrome are critically discussed. The commonly used diagnostic strategies, as well as the relevance of the lymphocyte transformation test, CD57+/CD3- cell count and CXCL13, are presented. Finally, the therapeutic options are described to give a balanced overview of all aspects of this disease.

Biological aspects of Lyme disease spirochetes: unique bacteria of the Borrelia burgdorferi species group

BACKGROUND

Borrelia burgdorferi sensu lato is a group of at least twelve closely related species some of which are responsible for Lyme disease, the most frequent zoonosis in Europe and the USA. Many of the biological features of Borrelia are unique in prokaryotes and very interesting not only from the medical viewpoint but also from the view of molecular biology.

METHODS

Relevant recent articles were searched using PubMed and Google search tools.

RESULTS AND CONCLUSION

This is a review of the biological, genetic and physiological features of the spirochete species group, Borrelia burgdorferi sensu lato. In spite of a lot of recent articles focused on B. burgdorferi sensu lato, many features of Borrelia biology remain obscure. It is one of the main reasons for persisting problems with prevention, diagnosis and therapy of Lyme disease. The aim of the review is to summarize ongoing current knowledge into a lucid and comprehensible form.

The pathogenesis of lyme neuroborreliosis: from infection to inflammation

This review describes the current knowledge of the pathogenesis of acute Lyme neuroborreliosis (LNB), from invasion to inflammation of the central nervous system. Borrelia burgdorferi (B.b.) enters the host through a tick bite on the skin and may disseminate from there to secondary organs, including the central nervous system. To achieve this, B.b. first has to evade the hostile immune system. In a second step, the borrelia have to reach the central nervous system and cross the blood-brain barrier. Once in the cerebrospinal fluid (CSF), the spirochetes elicit an inflammatory response. We describe current knowledge about the infiltration of leukocytes into the CSF in LNB. In the final section, we discuss the mechanisms by which the spirochetal infection leads to the observed neural dysfunction. To conclude, we construct a stringent concept of the pathogenesis of LNB.

Invasion of human neuronal and glial cells by an infectious strain of Borrelia burgdorferi

Human infection by Borrelia burgdorferi, the etiological agent for Lyme disease, can result in serious acute and late-term disorders including neuroborreliosis, a degenerative condition of the peripheral and central nervous systems. To examine the mechanisms involved in the cellular pathogenesis of neuroborreliosis, we investigated the ability of B. burgdorferi to attach to and/or invade a panel of human neuroglial and cortical neuronal cells. In all neural cells tested, we observed B. burgdorferi in association with the cell by confocal microscopy. Further analysis by differential immunofluorescent staining of external and internal organisms, and a gentamicin protection assay demonstrated an intracellular localization of B. burgdorferi. A non-infectious strain of B. burgdorferi was attenuated in its ability to associate with these neural cells, suggesting that a specific borrelial factor related to cellular infectivity was responsible for the association. Cytopathic effects were not observed following infection of these cell lines with B. burgdorferi, and internalized spirochetes were found to be viable. Invasion of neural cells by B. burgdorferi provides a putative mechanism for the organism to avoid the host's immune response while potentially causing functional damage to neural cells during infection of the CNS.