Borrelia miyamotoi Activates Human Dendritic Cells and Elicits T Cell Responses.

The spirochete Borrelia miyamotoi has recently been shown to cause relapsing fever. Like the Lyme disease agent, Borrelia burgdorferi, B. miyamotoi is transmitted through the bite of infected ticks; however, little is known about the response of the immune system upon infection. Dendritic cells (DCs) play a central role in the early immune response against B. burgdorferi We investigated the response of DCs to two different strains of B. miyamotoi using in vitro and ex vivo models and compared this to the response elicited by B. burgdorferi. Our findings show that B. miyamotoi is phagocytosed by monocyte-derived DCs, causing upregulation of activation markers and production of proinflammatory cytokines in a similar manner to B. burgdorferi. Recognition of B. miyamotoi was demonstrated to be partially mediated by TLR2. DCs migrated out of human skin explants upon inoculation of the skin with B. miyamotoi. Finally, we showed that B. miyamotoi-stimulated DCs induced proliferation of naive CD4+ and CD8+ T cells to a larger extent than B. burgdorferi. In conclusion, we show in this study that DCs respond to and mount an immune response against B. miyamotoi that is similar to the response to B. burgdorferi and is able to induce T cell proliferation.

Hepatitis B and C testing strategies in healthcare and community settings in the EU/EEA: A systematic review.

An estimated 9 million individuals are chronically infected with hepatitis B virus (HBV) and hepatitis C virus (HCV) across the European Union/European Economic Area (EU/EEA), many of which are yet to be diagnosed. We performed a systematic review to identify interventions effective at improving testing offer and uptake in the EU/EEA. Original research articles published between 1 January 2008 and 1 September 2017 were retrieved from PubMed and EMBASE. Search strings combined terms for HBV/HCV, intervention, testing and geographic terms (EU/EEA). Out of 8331 records retrieved, 93 studies were selected. Included studies reported on testing initiatives in primary health care (9), hospital (12), other healthcare settings (31) and community settings (41). Testing initiatives targeted population groups such as migrants, drug users, prisoners, pregnant women and the general population. Testing targeted to populations at higher risk yielded high coverage rates in many settings. Implementation of novel testing approaches, including dried blood spot (DBS) testing, was associated with increased coverage in several settings including drug services, pharmacies and STI clinics. Community-based testing services were effective in reaching populations at higher risk for infection, vulnerable and hard-to-reach populations. In conclusion, our review identified several successful testing approaches implemented in healthcare and community settings, including testing approaches targeting groups at higher risk, community-based testing services and DBS testing. Combining a diverse set of testing opportunities within national testing strategies may lead to higher impact both in terms of testing coverage and in terms of reduction, on the undiagnosed fraction.

MRP8/14 does not contribute to dissemination or inflammation in a murine model of Lyme borreliosis.

Myeloid-related protein (MRP)8 and MRP14 form a complex (MRP8/14) that is released by activated neutrophils and monocytes during infection. MRP8/14 has been shown to have bacteriostatic activity in vitro against Borrelia burgdorferi, the spirochete that causes Lyme borreliosis. Furthermore, levels of MRP8/14 have been shown to be elevated in the joints of patients with Lyme arthritis. We hypothesized that MRP8/14 has a protective effect during B. burgdorferi infection. To determine the role of MRP8/14 in the immune response to B. burgdorferi, we studied the course of B. burgdorferi infection in wildtype (wt) and mrp14-/- mice. In addition, we studied the response of leukocytes from mice lacking MRP8/14 to B. burgdorferi ex vivo. We demonstrated similar levels of B. burgdorferi dissemination, cytokine and immunoglobulin production in infected wt and mrp14-/- mice after 21 days. Neutrophils and monocytes lacking MRP8/14 were undiminished in their ability to become activated or phagocytose B. burgdorferi. In conclusion, we did not find a central role of MRP8/14 in the immune response against B. burgdorferi. As the levels of MRP8/14 in the serum of infected mice were low, we speculate that MRP8/14 is not released in levels great enough to influence the course of B. burgdorferi infection.

Investigating Human Dendritic Cell Immune Responses to Borrelia burgdorferi.

Dendritic cells (DCs) are professional antigen-presenting cells that recognize and phagocytose pathogens, and help to orchestrate adaptive immune responses to combat them. DCs are abundant in the skin where Borrelia burgdorferi first enters the body during a tick bite, and are thus critical in determining the initial stages of the innate and adaptive immune responses against Borrelia. Here, we describe two methods to study the response of DCs to Borrelia; an in vitro approach using monocyte-derived DCs (moDCs) and an ex vivo approach using a human skin model.

Borrelia burgdorferi Induces TLR2-Mediated Migration of Activated Dendritic Cells in an Ex Vivo Human Skin Model.

Borrelia burgdorferi is transmitted into the skin of the host where it encounters and interacts with two dendritic cell (DC) subsets; Langerhans cells (LCs) and dermal DCs (DDCs). These cells recognize pathogens via pattern recognition receptors, mature and migrate out of the skin into draining lymph nodes, where they orchestrate adaptive immune responses. In order to investigate the response of skin DCs during the early immunopathogenesis of Lyme borreliosis, we injected B. burgdorferi intradermally into full-thickness human skin and studied the migration of DCs out of the skin, the activation profile and phenotype of migrated cells. We found a significant increase in the migration of LCs and DDCs in response to B. burgdorferi. Notably, migration was prevented by blocking TLR2. DCs migrated from skin inoculated with higher numbers of spirochetes expressed significantly higher levels of CD83 and produced pro-inflammatory cytokines. No difference was observed in the expression of HLA-DR, CD86, CD38, or CCR7. To conclude, we have established an ex vivo human skin model to study DC-B. burgdorferi interactions. Using this model, we have demonstrated that B. burgdorferi-induced DC migration is mediated by TLR2. Our findings underscore the utility of this model as a valuable tool to study immunity to spirochetal infections.

Borrelia burgdorferi clinical isolates induce human innate immune responses that are not dependent on genotype.

Borrelia burgdorferi can be categorized based on restriction fragment length polymorphism analysis into ribosomal spacer type (RST) 1, 2 and 3. A correlation between RST type and invasiveness of Borrelia isolates has been demonstrated in clinical studies and experimental models, and RST 1 isolates are more likely to cause disseminated disease than RST 3 isolates. We hypothesized that this could partially be due to increased susceptibility of RST 3 isolates to killing by the innate immune system early in infection. Thus, we investigated the interaction of five RST 1 and five RST 3 isolates with various components of the human innate immune system in vitro. RST 3 isolates induced significantly greater upregulation of activation markers in monocyte-derived dendritic cells compared to RST 1 isolates at a low multiplicity of infection. However, RST 1 isolates stimulated greater interleukin-6 production. At a high multiplicity of infection no differences in dendritic cell activation or cytokine production were observed. In addition, we observed no differences in the ability of RST 1 and RST 3 isolates to activate monocytes or neutrophils and all strains were phagocytosed at a comparable rate. Finally, all isolates tested were equally resistant to complement-mediated killing, as determined by dark-field microscopy and a growth inhibition assay. In conclusion, we demonstrate that the RST 1 and 3 isolates showed no distinction in their susceptibility to the various components of the human immune system studied here, suggesting that other factors are responsible for their differential invasiveness.

Vitamin D3 metabolite calcidiol primes human dendritic cells to promote the development of immunomodulatory IL-10-producing T cells.

Vitamin D is recognized as a potent immunosuppressive drug. The suppressive effects of vitamin D are attributed to its physiologically active metabolite 1,25 dihydroxy vitamin D3 (calcitriol), which was shown, to prime dendritic cells (DCs) to promote the development of regulatory T (Treg) cells. Despite the potential benefit in treating autoimmune diseases, clinical application of calcitriol is hindered by deleterious side effects manifested by hypercalcemia and hypercalciuria. Conversely, the physiological precursors of calcitriol, vitamin D3 (cholecalciferol) and its first metabolite 25-hydroxy vitamin D3 (calcidiol) are widely applied in the clinic due to their low calcimic burden. However, the mechanisms by which cholecalciferol and calcidiol may modulate adaptive immunity remain elusive. This prompted us to unravel the immunosuppressive capacity of these precursors by assessing their influence on DC functions and the subsequent polarization of naïve CD4(+) T cells. In this study we show that, whereas cholecalciferol has insignificant effects on DC maturation and cytokine production, it only weakly primed DCs to induce suppressive T cells. However, like calcitriol, calcidiol not only exerted an inhibitory effect on DC maturation and cytokine production, and primed DCs to promote the development of suppressive IL-10-producing Treg cells. Strikingly, in contrast to the population of IL-10-producing Treg cells induced by calcitriol-primed DCs, the IL-10-producing Treg cells induced by calcidiol-primed DCs exhibited sustained IFN-γ production in face of their suppressive capacity. Experiments with the steroid synthesis inhibitor ketoconazole indicated that the immunomodulatory features of the precursors are dependent on their conversion into calcitriol. Collectively, calcidiol is a potent immune modulator, which may be more adequate than calcitriol for the treatment of chronic inflammatory diseases, since it is less hypercalcimic. This may be of particular interest for the treatment of allergic disease, where concurrent suppression and sustained IFN-γ production by Treg cells effectively counterbalance the Th2-dominated immune responses.

Ménage à trois: Borrelia, dendritic cells, and tick saliva interactions.

Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis, is inoculated into the skin during an Ixodes tick bite where it is recognised and captured by dendritic cells (DCs). However, considering the propensity of Borrelia to disseminate, it would appear that DCs fall short in mounting a robust immune response against it. Many aspects of the DC-driven immune response to Borrelia have been examined. Recently, components of tick saliva have been identified that sabotage DC responses and aid Borrelia infection. In this review, we summarise what is currently known about the immune response of DCs to Borrelia and explore the mechanisms by which Borrelia manages to circumvent this immune response, with or without the help of tick salivary proteins.