Infection of Interleukin 17 Receptor A-Deficient C3H Mice with Borrelia burgdorferi Does Not Affect Their Development of Lyme Arthritis and Carditis

Animal models of Lyme carditis. Understanding how to study a complex disease

Lyme carditis, a well-established manifestation of Lyme disease, has been studied in animal models to improve understanding of its pathogenesis. This review synthesizes existing literature on these models and associated disease mechanisms. Searches in MEDLINE, Embase, BIOSIS, and Web of Science yielded 53 articles (47 mice models and 6 other animal models). Key findings include: 1) Onset of carditis correlates with spirochete localization in the heart; 2) Carditis occurs within 10 days of infection, progressing to peak inflammation within 30 days; 3) Infiltrates were predominantly composed of Mac-1+ macrophages and were associated with increases in TNF-α, IL-1 and IL-12 cytokines; 4) Resolution of inflammation was primarily mediated by lymphocytes; 5) Immune system is a double-edged sword: it can play a role in the progression and severity of carditis, but can also have a protective effect. Animal models offer valuable insights into the evolution and pathophysiologic mechanisms of Lyme carditis.

The PD-1/PD-L1 pathway is induced during Borrelia burgdorferi infection and inhibits T cell joint infiltration without compromising bacterial clearance

The Lyme disease bacterial pathogen, Borrelia burgdorferi, establishes a long-term infection inside its mammalian hosts. Despite the continued presence of the bacteria in animal models of disease, inflammation is transitory and resolves spontaneously. T cells with limited effector functions and the inability to become activated by antigen, termed exhausted T cells, are present in many long-term infections. These exhausted T cells mediate a balance between pathogen clearance and preventing tissue damage resulting from excess inflammation. Exhausted T cells express a variety of immunoinhibitory molecules, including the molecule PD-1. Following B. burgdorferi infection, we found that PD-1 and its ligand PD-L1 are significantly upregulated on CD4+ T cells and antigen presenting cell subsets, respectively. Using mice deficient in PD-1, we found that the PD-1/PD-L1 pathway did not impact bacterial clearance but did impact T cell expansion and accumulation in the ankle joint and popliteal lymph nodes without affecting B cell populations or antibody production, suggesting that the PD-1/PD-L1 pathway may play a role in shaping the T cell populations present in affected tissues.

CD4 T cell responses in persistent Borrelia burgdorferi infection

Infection of mice with Borrelia burgdorferi (Bb), a tick-transmitted spirochete and the pathogen that causes Lyme disease in humans, triggers CD4 T cell activation in secondary lymphoid tissues, from which they disseminate into various infected tissues. Despite their activation and the appearance of CD4 T cell-dependent antibody responses, Bb establishes persistent infection in natural Bb reservoir hosts in the absence of overt disease, raising the question of the effectiveness of the anti-Bb T cell responses. Reviewing the existing literature, we propose that CD4 T cells might constitute a host cell target of Bb-mediated immune evasion, rendering these cells ineffective in orchestrating effective inflammatory responses and in supporting highly functional Bb-specific antibody induction. Supporting the induction of more effective CD4 T cell responses may help overcome Bb persistence.

Bone Marrow Mesenchymal Stem Cells (BMSCs) Transplantation Ameliorates Joint Severity and Inflammation in Rats with Arthritis

This study analyzed the action of Bone marrow mesenchymal stem cells (BMSCs) transplantation on arthritis rat model. Arthritis rat model was established using bovine type II collagen and CFA. BMSCs phenotype was assessed by flow cytometry and pathological changes was analyzed by H&E staining along with analysis of joint severity by AI score, inflammation by ELISA as well as level of NPY, MMP-2, and MMP-9. The form of passaged BMSCs was spindle shaped with positive expression of CD29 and CD44. The structure of articular cavity in arthritis rats was disordered with infiltration of inflammatory cells which were ameliorated by BMSCs transplantation. In addition, BMSCs treatment also significantly reduced AI value, the level of VEGF, IL-17 and TNF-α as well as decreased RANK/RANKL expression and increased OPG level. In conclusion, BMSCs transplantation ameliorates inflammation and severity in arthritis rats possibly through regulation of RANK/OPG, indicating that it might be used for the treatment of arthritis patients.

Immune Response to Borrelia: Lessons from Lyme Disease Spirochetes

The mammalian host responds to infection with Borrelia spirochetes through a highly orchestrated immune defense involving innate and adaptive effector functions aimed toward limiting pathogen burdens, minimizing tissue injury, and preventing subsequent reinfection. The evolutionary adaptation of Borrelia spirochetes to their reservoir mammalian hosts may allow for its persistence despite this immune defense. This review summarizes our current understanding of the host immune response to B. burgdorferi sensu lato, the most widely studied Borrelia spp. and etiologic agent of Lyme borreliosis. Pertinent literature will be reviewed with emphasis on in vitro, ex vivo and animal studies that influenced our understanding of both the earliest responses to B. burgdorferi as it enters the mammalian host and those that evolve as spirochetes disseminate and establish infection in multiple tissues. Our focus is on the immune response of inbred mice, the most commonly studied animal model of B. burgdorferi infection and surrogate for one of this pathogen's principle natural reservoir hosts, the white-footed deer mouse. Comparison will be made to the immune responses of humans with Lyme borreliosis. Our goal is to provide an understanding of the dynamics of the mammalian immune response during infection with B. burgdorferi and its relation to the outcomes in reservoir (mouse) and non-reservoir (human) hosts.

Chagas' cardiomyopathy and Lyme carditis: Lessons learned from two infectious diseases affecting the heart

Chagas' disease and Lyme disease are two endemic, vector-borne zoonotic infectious diseases that impact multiple organ systems, including the heart. Chagas' cardiomyopathy is a progressive process that can evolve into a dilated cardiomyopathy and heart failure several decades after the acute infection; in contrast, although early-disseminated Lyme carditis has been relatively well characterized, the sequelae of Lyme disease on the heart are less well-defined. A century of research on Chagas' cardiomyopathy has generated compelling data for pathophysiological models, evaluated the efficacy of therapy in large randomized controlled trials, and explored the social determinants of health impacting preventative measures. Recognizing the commonalities between Chagas' disease and Lyme disease, we speculate on whether some of the lessons learned from Chagas' cardiomyopathy may be applicable to Lyme carditis.

Arthritis is inhibited in Borrelia-primed and infected interleukin-17A-deficient mice after administration of anti-gamma-interferon, anti-tumor necrosis factor alpha and anti-interleukin-6 antibodies

The role that cytokines play in the induction of Lyme arthritis is gradually being delineated. We showed previously that severe arthritis developed in a T-cell-driven murine model, even in mice lacking interleukin-17A (IL-17A) and administered anti-gamma-interferon (IFN-γ) antibody. Increased levels of tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), two pro-inflammatory cytokines, were detected in cultures of popliteal lymph node cells obtained from these mice. We hypothesized that concomitantly administered anti-IL-6, anti-TNF-α and anti-IFN-γ antibodies would inhibit the development of arthritis in IL-17A-deficient mice. Our results showed that swelling of the hind paws and histopathological changes consistent with arthritis were significantly reduced in IL-17A-deficient mice that administered the three anti-cytokine antibodies. These results suggest that treatment with multiple anti-cytokine antibodies can abrogate the induction of Lyme arthritis in mice.

Induction of Interleukin 10 by Borrelia burgdorferi Is Regulated by the Action of CD14-Dependent p38 Mitogen-Activated Protein Kinase and cAMP-Mediated Chromatin Remodeling

Host genotype influences the severity of murine Lyme borreliosis, caused by the spirochetal bacterium Borrelia burgdorferi C57BL/6 (B6) mice develop mild Lyme arthritis, whereas C3H/HeN (C3H) mice develop severe Lyme arthritis. Differential expression of interleukin 10 (IL-10) has long been associated with mouse strain differences in Lyme pathogenesis; however, the underlying mechanism(s) of this genotype-specific IL-10 regulation remained elusive. Herein we reveal a cAMP-mediated mechanism of IL-10 regulation in B6 macrophages that is substantially diminished in C3H macrophages. Under cAMP and CD14-p38 mitogen-activated protein kinase (MAPK) signaling, B6 macrophages stimulated with B. burgdorferi produce increased amounts of IL-10 and decreased levels of arthritogenic cytokines, including tumor necrosis factor (TNF). cAMP relaxes chromatin, while p38 increases binding of the transcription factors signal transducer and activator of transcription 3 (STAT3) and specific protein 1 (SP1) to the IL-10 promoter, leading to increased IL-10 production in B6 bone marrow-derived monocytes (BMDMs). Conversely, macrophages derived from arthritis-susceptible C3H mice possess significantly less endogenous cAMP, produce less IL-10, and thus are ill equipped to mitigate the damaging consequences of B. burgdorferi-induced TNF. Intriguingly, an altered balance between anti-inflammatory and proinflammatory cytokines and CD14-dependent regulatory mechanisms also is operative in primary human peripheral blood-derived monocytes, providing potential insight into the clinical spectrum of human Lyme disease. In line with this notion, we have demonstrated that cAMP-enhancing drugs increase IL-10 production in myeloid cells, thus curtailing inflammation associated with murine Lyme borreliosis. Discovery of novel treatments or repurposing of FDA-approved cAMP-modulating medications may be a promising avenue for treatment of patients with adverse clinical outcomes, including certain post-Lyme complications, in whom dysregulated immune responses may play a role.

Borrelia-primed and -infected mice deficient of interleukin-17 develop arthritis after neutralization of gamma-interferon

The immune mechanisms responsible for development of Lyme arthritis are partially understood with interleukin-17 (IL-17) and gamma-interferon (IFN-γ) playing a generally accepted role. Elevated levels of IL-17 and/or IFN-γ have been reported in samples from human Lyme arthritis patients and experimental mice. In addition, IL-17 and IFN-γ have been implicated in the onset of arthritis in Borrelia-primed and -infected C57BL/6 mice. Recently, we showed that IL-17-deficient mice developed swelling and histopathological changes consistent with arthritis in the presence of high levels of IFN-γ. We hypothesized that neutralization of IFN-γ in IL-17-deficient mice would inhibit Borrelia-induced arthritis. Our results, however, showed that swelling of the hind paws and histopathological changes of arthritis did not differ between Borrelia-primed and -infected IL-17-deficient and wild-type mice with or without neutralization of IFN-γ. We also found higher levels of tumor necrosis factor alpha (TNF-α) and IL-6 in the popliteal lymph node cells of Borrelia-primed and -infected IL-17-deficient mice after neutralization of IFN-γ. These results suggest that multiple cytokines interact in the development of Borrelia-induced arthritis.

The Lyme Disease Pathogen Borrelia burgdorferi Infects Murine Bone and Induces Trabecular Bone Loss

Lyme disease is caused by members of the Borrelia burgdorferisensu lato species complex. Arthritis is a well-known late-stage pathology of Lyme disease, but the effects of B. burgdorferi infection on bone at sites other than articular surfaces are largely unknown. In this study, we investigated whether B. burgdorferi infection affects bone health in mice. In mice inoculated with B. burgdorferi or vehicle (mock infection), we measured the presence of B. burgdorferi DNA in bones, bone mineral density (BMD), bone formation rates, biomechanical properties, cellular composition, and two- and three-dimensional features of bone microarchitecture. B. burgdorferi DNA was detected in bone. In the long bones, increasing B. burgdorferi DNA copy number correlated with reductions in areal and trabecular volumetric BMDs. Trabecular regions of femora exhibited significant, copy number-correlated microarchitectural disruption, but BMD, microarchitectural, and biomechanical properties of cortical bone were not affected. Bone loss in tibiae was not due to increased osteoclast numbers or bone-resorbing surface area, but it was associated with reduced osteoblast numbers, implying that bone loss in long bones was due to impaired bone building. Osteoid-producing and mineralization activities of existing osteoblasts were unaffected by infection. Therefore, deterioration of trabecular bone was not dependent on inhibition of osteoblast function but was more likely caused by blockade of osteoblastogenesis, reduced osteoblast survival, and/or induction of osteoblast death. Together, these data represent the first evidence that B. burgdorferi infection induces bone loss in mice and suggest that this phenotype results from inhibition of bone building rather than increased bone resorption.

Macrophage LTB4 drives efficient phagocytosis of Borrelia burgdorferi via BLT1 or BLT2

Unresolved experimental Lyme arthritis in C3H 5-lipoxygenase (5-LOX)^-/- mice is associated with impaired macrophage phagocytosis of Borrelia burgdorferi In the present study, we further investigated the effects of the 5-LOX metabolite, leukotriene (LT)B₄ on phagocytosis of B. burgdorferi Bone marrow-derived macrophages (BMDMs) from 5-LOX^-/- mice were defective in the uptake and killing of B. burgdorferi from the earliest stages of spirochete internalization. BMDMs from mice deficient for the LTB₄ high-affinity receptor (BLT1^-/-) were also unable to efficiently phagocytose B. burgdorferi Addition of exogenous LTB₄ augmented the phagocytic capability of BMDMs from both 5-LOX^-/- and BLT1^-/- mice, suggesting that the low-affinity LTB₄ receptor, BLT2, might be involved. Blocking BLT2 activity with the specific antagonist, LY255283, inhibited phagocytosis in LTB₄-stimulated BLT1^-/- BMDMs, demonstrating a role for BLT2. However, the lack of a phagocytic defect in BLT2^-/- BMDMs suggested that this was a compensatory effect. In contrast, 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid, a natural BLT2-specific high-affinity ligand, and resolvin E1, a BLT1 agonist, were both unable to boost phagocytosis in BMDMs from either 5-LOX^-/- or BLT1^-/- mice, suggesting a specific role for LTB₄ in mediating phagocytosis in murine macrophages. This study demonstrates that LTB₄ promotes macrophage phagocytosis of bacteria via BLT1, and that BLT2 can fulfill this role in the absence of BLT1.

CD4+ cell-derived interleukin-17 in a model of dysregulated, Borrelia-induced arthritis

Lyme borreliosis, which is caused in the United States by the spirochete Borrelia burgdorferi, may manifest as different arrays of signs, symptoms and severities between infected individuals. Recent studies have indicated that particularly severe forms of Lyme borreliosis in humans are associated with an increased Th17 response. Here, we hypothesized that a murine model combining the dysregulated immune response of an environment lacking interleukin-10 (IL-10) with a robust T-cell-driven inflammatory response would reflect arthritis associated with the production of IL-17 by CD4+ cells. We demonstrate that IL-10 regulates the production of IL-17 by Borrelia-primed CD4+ cells early after interaction with Lyme spirochetes in vitro and that infection of Borrelia-primed mice with B. burgdorferi leads to significant production of IL-17 that contributes to the development of severe arthritis. These results extend our previous findings by demonstrating that a dysregulated adaptive immune response to Lyme spirochetes can contribute to severe, Th17-associated arthritis. These findings may lead to therapeutic measures for individuals with particularly severe symptoms of Lyme borreliosis.

CXCR2 Mediates Brucella-Induced Arthritis in Interferon γ-Deficient Mice

BACKGROUND

Brucella species are facultative intracellular gram-negative bacteria that cause brucellosis, a common global zoonosis. Infection of the joints is the most common focal complication of brucellosis in humans. The purpose of this study was to identify mediators of focal inflammation during brucellosis.

METHODS

Wild-type (WT) mice are naturally resistant to Brucella infection; therefore, we infected anti-interferon γ (IFN-γ)-treated, or IFN-γ(-/-) mice with Brucella to induce osteoarticular and musculoskeletal inflammation, as we previously described. Mice were infected intraperitoneally with Brucella melitensis, and the clinical course of disease, histopathologic changes, and cytokine levels were compared among groups.

RESULTS

Rag1(-/-) mice (B- and T-cell deficient) and µMT(-/-) mice (B-cell deficient) developed paw inflammation at a similar rate and severity as WT mice following infection with B. melitensis and treatment with anti-IFN-γ. Joints from B. melitensis-infected IFN-γ(-/-) mice had markedly increased levels of CCR2 and CXCR2 ligands. While anti-IFN-γ-treated CCR2(-/-) and WT mice behaved similarly, anti-IFN-γ-treated CXCR2(-/-) or IFN-γ(-/-)/CXCR2(-/-) mice had strikingly reduced focal swelling relative to anti-IFN-γ-treated WT or IFN-γ(-/-) mice, respectively. Additionally, neutrophil recruitment was dependent on CXCR2.

CONCLUSIONS

Adaptive immune cells and CCR2 are dispensable, while CXCR2 is necessary for Brucella-induced focal neutrophil recruitment and inflammation.