Regulatory T Cells Contribute to Resistance against Lyme Arthritis

Lyme disease and the pursuit of a clinical cure

Lyme disease, caused by the spirochete Borrelia burgdorferi, is the most common vector-borne illness in the United States. Many aspects of the disease are still topics of controversy within the scientific and medical communities. One particular point of debate is the etiology behind antibiotic treatment failure of a significant portion (10-30%) of Lyme disease patients. The condition in which patients with Lyme disease continue to experience a variety of symptoms months to years after the recommended antibiotic treatment is most recently referred to in the literature as post treatment Lyme disease syndrome (PTLDS) or just simply post treatment Lyme disease (PTLD). The most commonly proposed mechanisms behind treatment failure include host autoimmune responses, long-term sequelae from the initial Borrelia infection, and persistence of the spirochete. The aims of this review will focus on the in vitro, in vivo, and clinical evidence that either validates or challenges these mechanisms, particularly with regard to the role of the immune response in disease and resolution of the infection. Next generation treatments and research into identifying biomarkers to predict treatment responses and outcomes for Lyme disease patients are also discussed. It is essential that definitions and guidelines for Lyme disease evolve with the research to translate diagnostic and therapeutic advances to patient care.

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.

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.

Lyme arthritis: linking infection, inflammation and autoimmunity

Infectious agents can trigger autoimmune responses in a number of chronic inflammatory diseases. Lyme arthritis, which is caused by the tick-transmitted spirochaete Borrelia burgdorferi, is effectively treated in most patients with antibiotic therapy; however, in a subset of patients, arthritis can persist and worsen after the spirochaete has been killed (known as post-infectious Lyme arthritis). This Review details the current understanding of the pathogenetic events in Lyme arthritis, from initial infection in the skin, through infection of the joints, to post-infectious chronic inflammatory arthritis. The central feature of post-infectious Lyme arthritis is an excessive, dysregulated pro-inflammatory immune response during the infection phase that persists into the post-infectious period. This response is characterized by high amounts of IFNγ and inadequate amounts of the anti-inflammatory cytokine IL-10. The consequences of this dysregulated pro-inflammatory response in the synovium include impaired tissue repair, vascular damage, autoimmune and cytotoxic processes, and fibroblast proliferation and fibrosis. These synovial characteristics are similar to those in other chronic inflammatory arthritides, including rheumatoid arthritis. Thus, post-infectious Lyme arthritis provides a model for other chronic autoimmune or autoinflammatory arthritides in which complex immune responses can be triggered and shaped by an infectious agent in concert with host genetic factors.

Predicting Lyme Disease From Patients' Peripheral Blood Mononuclear Cells Profiled With RNA-Sequencing

Although widely prevalent, Lyme disease is still under-diagnosed and misunderstood. Here we followed 73 acute Lyme disease patients and uninfected controls over a period of a year. At each visit, RNA-sequencing was applied to profile patients' peripheral blood mononuclear cells in addition to extensive clinical phenotyping. Based on the projection of the RNA-seq data into lower dimensions, we observe that the cases are separated from controls, and almost all cases never return to cluster with the controls over time. Enrichment analysis of the differentially expressed genes between clusters identifies up-regulation of immune response genes. This observation is also supported by deconvolution analysis to identify the changes in cell type composition due to Lyme disease infection. Importantly, we developed several machine learning classifiers that attempt to perform various Lyme disease classifications. We show that Lyme patients can be distinguished from the controls as well as from COVID-19 patients, but classification was not successful in distinguishing those patients with early Lyme disease cases that would advance to develop post-treatment persistent symptoms.