Anti-CD25 antibody treatment of mice vaccinated and challenged with Borrelia spp. does not exacerbate arthritis but inhibits borreliacidal antibody production

Effects of Regulatory T Cell Depletion in BALB/c Mice Infected with Low Doses of Borrelia burgdorferi

We previously demonstrated that a depletion of regulatory T (Treg) cells in Lyme arthritis-resistant C57BL/6 mice leads to pathological changes in the tibiotarsal joints following infection with Borrelia burgdorferi. Here, we assessed the effects of Treg cells on the response to B. burgdorferi infection in BALB/c mice, which exhibit infection-dose-dependent disease and a different sequence of immune events than C57BL/6 mice. The depletion of Treg cells prior to infection with 1 × 10², but not 5 × 10³, organisms led to increased swelling of the tibiotarsal joints. However, Treg cell depletion did not significantly affect the development of histopathology at these low doses of infection. BALB/c mice depleted of Treg cells before infection with 1 × 10³ spirochetes harbored a higher borrelial load in the hearts and exhibited higher levels of serum interleukin-10 five weeks later. These results indicate that Treg cells regulate certain aspects of the response to B. burgdorferi in a mouse strain that may display a range of disease severities. As the presentation of Lyme disease may vary among humans, it is necessary to consider multiple animal models to obtain a complete picture of the various means by which Treg cells affect the host response to B. burgdorferi.

Regulatory T Cells Contribute to Resistance against Lyme Arthritis

The symptoms of Lyme disease are caused by inflammation induced by species of the Borrelia burgdorferi sensu lato complex. The various presentations of Lyme disease in the population suggest that differences exist in the intensity and regulation of the host response to the spirochete. Previous work has described correlations between the presence of regulatory T cells and recovery from Lyme arthritis. However, the effects of Foxp3-expressing CD4⁺ T cells existing prior to, and during, B. burgdorferi infection have not been well characterized. Here, we used C57BL/6 "depletion of regulatory T cell" mice to assess the effects these cells have on the arthritis-resistant phenotype characteristic of this mouse strain. We showed that depletion of regulatory T cells prior to infection with B. burgdorferi resulted in sustained swelling, as well as histopathological changes, of the tibiotarsal joints that were not observed in infected control mice. Additionally, in vitro stimulation of splenocytes from these regulatory T cell-depleted mice resulted in increases in gamma interferon and interleukin-17 production and decreases in interleukin-10 production that were not evident among splenocytes of infected mice in which Treg cells were not depleted. Depletion of regulatory T cells at various times after infection also induced rapid joint swelling. Collectively, these findings provide evidence that regulatory T cells existing at the time of, and possibly after, B. burgdorferi infection may play an important role in limiting the development of arthritis.

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.

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.

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.

Arthritis is developed in Borrelia-primed and -infected mice deficient of interleukin-17

Interleukin-17 (IL-17) has been shown to participate in the development of Lyme arthritis in experimental mice. For example, neutralization of IL-17 with antibodies inhibits induction of arthritis in Borrelia-primed and -infected C57BL/6 wild-type mice. We hypothesized that mice lacking IL-17 would fail to develop Borrelia-induced arthritis. IL-17-deficient and wild-type C57BL/6 mice were primed with heat-inactivated Borrelia and then infected with viable spirochetes 3 weeks later. No swelling or major histopathological changes of the hind paws were detected in IL-17-deficient or wild-type mice that were primed with Borrelia or infected with viable spirochetes. By contrast, IL-17-deficient and wild-type mice that were primed and subsequently infected with heterologous Borrelia developed severe swelling and histopathological changes of the hind paws. In addition, Borrelia-primed and -infected IL-17-deficient mice exhibited elevated gamma-interferon (IFN-γ) levels in sera and increased frequencies of IFN-γ-expressing lymphocytes in popliteal lymph nodes compared to Borrelia-primed and -infected wild-type mice. These results demonstrate that IL-17 is not required for development of severe pathology in response to infection with Borrelia burgdorferi, but may contribute to disease through an interaction with IFN-γ.

Interleukin-10 (IL-10) inhibits Borrelia burgdorferi-induced IL-17 production and attenuates IL-17-mediated Lyme arthritis

Previous studies have shown that cells and cytokines associated with interleukin-17 (IL-17)-driven inflammation are involved in the arthritic response to Borrelia burgdorferi infection. Here, we report that IL-17 is a contributing factor in the development of Lyme arthritis and show that its production and histopathological effects are regulated by interleukin-10 (IL-10). Spleen cells obtained from B. burgdorferi-infected, "arthritis-resistant" wild-type C57BL/6 mice produced low levels of IL-17 following stimulation with the spirochete. In contrast, spleen cells obtained from infected, IL-10-deficient C57BL/6 mice produced a significant amount of IL-17 following stimulation with B. burgdorferi. These mice developed significant arthritis, including erosion of the bones in the ankle joints. We further show that treatment with antibody to IL-17 partially inhibited the significant hind paw swelling and histopathological changes observed in B. burgdorferi-infected, IL-10-deficient mice. Taken together, these findings provide additional evidence of a role for IL-17 in Lyme arthritis and reveal an additional regulatory target of IL-10 following borrelial infection.

Hamster and murine models of severe destructive Lyme arthritis

Arthritis is a frequent complication of infection in humans with Borrelia burgdorferi. Weeks to months following the onset of Lyme borreliosis, a histopathological reaction characteristic of synovitis including bone, joint, muscle, or tendon pain may occur. A subpopulation of patients may progress to a chronic, debilitating arthritis months to years after infection which has been classified as severe destructive Lyme arthritis. This arthritis involves focal bone erosion and destruction of articular cartilage. Hamsters and mice are animal models that have been utilized to study articular manifestations of Lyme borreliosis. Infection of immunocompetent LSH hamsters or C3H mice results in a transient synovitis. However, severe destructive Lyme arthritis can be induced by infecting irradiated hamsters or mice and immunocompetent Borrelia-vaccinated hamsters, mice, and interferon-gamma- (IFN-γ-) deficient mice with viable B. burgdorferi. The hamster model of severe destructive Lyme arthritis facilitates easy assessment of Lyme borreliosis vaccine preparations for deleterious effects while murine models of severe destructive Lyme arthritis allow for investigation of mechanisms of immunopathology.

Anti-CD25 antibody-mediated depletion of effector T cell populations enhances susceptibility of mice to acute but not chronic Toxoplasma gondii infection

Natural regulatory T cells (Tregs) constitutively express the IL-2R alpha-chain (CD25) on their surface. Consequently, administration of anti-CD25 Abs is a commonly used technique to deplete Treg populations in vivo. However, activated effector T cells may also transiently express CD25, and are thus also potential targets for anti-CD25 Abs. In this study using Toxoplasma gondii as a model proinflammatory infection, we have examined the capacity of anti-CD25 Abs to target effector T cell populations during an inflammatory episode, to determine to what extent that this action may modulate the outcome of disease. Anti-CD25 Ab-treated C57BL/6 mice displayed significantly reduced CD4(+) T cell IFN-gamma production during acute T. gondii infection and exhibited reduced weight loss and liver pathology during early acute infection; aspects of infection previously associated with effector CD4(+) T cell responses. In agreement, anti-CD25 Ab administration impaired parasite control and caused mice to succumb to infection during late acute/early chronic stages of infection with elevated tissue parasite burdens. In contrast, anti-CD25 Ab treatment of mice with established chronic infections did not markedly affect brain parasite burdens, suggesting that protective T cell populations do not express CD25 during chronic stages of T. gondii infection. In summary, we have demonstrated that anti-CD25 Abs may directly abrogate effector T cell responses during an inflammatory episode, highlighting important limitations of the use of anti-CD25 Ab administration to examine Treg function during inflammatory settings.

Interleukin-23 is required for development of arthritis in mice vaccinated and challenged with Borrelia species

We recently hypothesized that T helper 17 (Th17) cells and their associated cytokines are involved in the development of arthritis following infection with Borrelia burgdorferi. Here, we show that interleukin-23 (IL-23), a survival factor for Th17 cells, is required for the induction of arthritis in mice vaccinated with B. burgdorferi strain 297 and challenged with "Borrelia bissettii." When Borrelia-vaccinated and -challenged mice were given antibodies to the p19 subunit of IL-23, they failed to develop the histopathological changes observed in untreated vaccinated and challenged mice. In addition, viable B. bissettii organisms stimulated the secretion of IL-17 from Borrelia-immune lymph node cells during in vitro culture. When anti-IL-23 p19 antibody was included in cultures of B. bissettii organisms and Borrelia-immune lymph node cells, the production of IL-17 was reduced to levels observed in cultures containing immune cells alone. Taken together, these results support the hypothesis that Th17 cell-associated cytokines are involved in the development of Borrelia-mediated arthritis. These findings provide insight into previously overlooked immune mechanisms responsible for the development of Lyme arthritis.

Arthritis develops but fails to resolve during inhibition of cyclooxygenase 2 in a murine model of Lyme disease

OBJECTIVE

Recent studies have implicated products of cyclooxygenase 2 (COX-2) in not only induction but also resolution of the inflammatory response; however, the contribution of COX-2 products to the in vivo response to infection is unknown. The aim of this study was to determine the contribution of COX-2 to temporal regulation of the inflammatory response to infection in a murine model of Lyme arthritis.

METHODS

Experimental Lyme disease was induced in both arthritis-resistant DBA/2J and arthritis-susceptible C3H/HeJ mice by inoculation in the hind footpads with Borrelia burgdorferi. COX-2 inhibitors were administered daily, and their effect on arthritis pathology was assessed at various time points postinfection. The COX-2 deficiency was also backcrossed onto both DBA and C3H backgrounds to confirm the findings from COX-2 inhibitor-treated mice.

RESULTS

In COX-2 inhibitor-treated or COX-2-/- C3H mice, arthritis developed normally but did not resolve. Cessation of COX-2 inhibitor treatment on day 14 postinfection did not induce resolution of arthritis, indicating an early onset for the molecular mechanisms governing resolution. The lack of resolution of arthritis correlated with altered COX-2 and cytosolic phospholipase A2 messenger RNA levels in the joints of C3H mice. In addition, the proresolution lipid molecule 15-deoxy-Delta12,14-prostaglandin J2 was produced in response to B burgdorferi infection, and its production was attenuated by the inhibition of COX-2.

CONCLUSION

Our results demonstrate that early production of COX-2 products is necessary for resolution of the inflammatory arthritis induced by Borrelia infection, and that COX-2 inhibition may result in prolonged inflammatory states, possibly by inhibition of proresolution eicosanoids.

Role of IL-17, transforming growth factor-beta, and IL-6 in the development of arthritis and production of anti-outer surface protein A borreliacidal antibodies in Borrelia-vaccinated and -challenged mice

We showed recently that the adaptive immune events leading to the development of arthritis in Borrelia burgdorferi isolate 297-vaccinated and Borrelia bissettii-challenged mice involve IL-17. Here, we show in Borrelia-vaccinated and -challenged mice that two cytokines known to induce the production of IL-17, IL-6 and transforming growth factor (TGF)-beta, are also involved in the development of arthritis. Vaccinated and challenged mice administered either anti-TGF-beta or anti-IL-6 antibodies developed histopathologic changes of the hind paws similar to or greater than untreated control mice. By contrast, simultaneous blockage of these cytokines reduced the severity of arthritis in Borrelia-vaccinated and -challenged mice. Moreover, administration of anti-IL-17 antibodies to these dual-antibody-treated mice completely prevented the development of histopathologic changes of the ankle joints, significantly reduced edema of the hind paws, and prevented the production of anti-outer surface protein A borreliacidal antibodies. These findings demonstrate a role for the combined effects of IL-17, IL-6, and TGF-beta in the adaptive immune events leading to the development of Borrelia-induced arthritis.

Anti-p19 antibody treatment exacerbates lyme arthritis and enhances borreliacidal activity

Considerable effort has been made to elucidate the mechanism of Lyme arthritis. We focused on p19, a cell cycle-regulating molecule, because it is known to inhibit cell cycle division of T lymphocytes which may be responsible for the induction of arthritis. We show that anti-p19 antibody treatment enhances the inflammatory response normally detected at the tibiotarsal joints of Borrelia burgdorferi-vaccinated and Borrelia bissettii-challenged mice. Specifically, anti-p19 antibody treatment augmented the severity of inflammation within the synovial and subsynovial tissue. Moreover, treatment with anti-p19 antibody caused severe erosion of cartilage and bone with ankle joint destruction. In addition, anti-p19 antibody treatment of Borrelia-vaccinated and -challenged mice enhanced the borreliacidal antibody response, especially against the vaccine isolate. The novel activities of anti-p19 antibody show that p19 may be an important therapeutic site for the treatment of Lyme arthritis.