title: Adaptive Immunity in Alphavirus-Induced Disease – A Focus on Interleukin-17
Creators: name: Mostafavi, Helen
Publisher: name: Griffith University
Year: 2022
Subjects: subject: Alphavirus
subject: Interleukin-17
subject: Arthritic disease

description: Mosquito-borne arthritogenic alphaviruses such as Ross River virus (RRV) are responsible for outbreaks of arthritic disease in Australia and worldwide. RRV induces the development of painful, incapacitating musculoskeletal inflammation which can last from months to years after initial acute disease, and is mediated by host cellular immune responses. While previous studies have described the role of innate immune responses in RRV infection, the role of adaptive immune responses still remain poorly understood. In addition, no current vaccine or specific-treatment exists, with patients relying on analgesia, palliative care or disease modifying anti-rheumatic drugs. RRV shares similar characteristics with rheumatoid arthritis (RA), such as the development of arthritis, arthralgia, and the influx of proinflammatory mediators. The IL-17 signaling pathway, specifically the role of IL-17‒producing T cells, has been widely described to contribute to inflammatory responses and bone/cartilage damage in RA. Further, inhibiting IL-17 has been shown to be an effective treatment strategy in alleviating RA-associated pathology and disease severity. Therefore, in this thesis we aimed to investigate if the IL-17 pathway contributed to RRV disease by tracking it throughout the course of infection, and if inhibiting IL-17 would alleviate disease and dampen inflammatory responses in RRV-infected mice. Mice were infected with RRV, and feet and muscle tissues collected at the pre-onset phase of disease, disease onset, peak disease, and disease recovery for various analyses. Confocal microscopy and flow cytometry analysis revealed the presence of IL-17A+ and IL-17F+ cell subsets produced by CD4+ and CD8+ T cells in the feet and muscle of RRV-infected mice. These cells followed the course of disease, in that they peaked during severe disease before contracting while mice started to recover. However, we found T cells and IL-17+ T cell persisted at the recovery phase when disease had fully resolved. Interestingly, we also found that IL-17‒producing neutrophils are important contributors of IL-17 in the cellular infiltrate during peak disease. In addition, treating RRV-infected mice with an anti-IL-17A/F monoclonal antibody significantly reduced disease severity and led to decreased proinflammatory proteins, reduced cellular infiltration in synovial tissues, decreased cartilage damage at peak disease, and reduced viral titres during early infection. Further, we demonstrated that anti-IL-17A/F treatment triggered a shift in the transcriptional profile of both leukocyte infiltrates and synovial stromal cells by downregulating proinflammatory genes, and upregulating genes associated with tissue repair and cell homeostasis. In the final component of this thesis, we investigated the role of the stromal compartment and how it interplays with the leukocyte compartment during alphavirus infection, which remains poorly understood. We therefore developed a joint and muscle organotypic cell culture model which was susceptible to RRV infection and reflected the immune responses in the leukocyte and stromal compartment observed in in vivo RRV infection. To our knowledge, this is the first organotypic cell culture model for not just RRV-induced infection, but also the first organotypic model for alphavirus-induced infection, as previous studies have relied on either the use of animal models, or monocultures of human/murine primary cells or commercial cell lines. Altogether, this thesis highlights a previously uncharacterised role of the IL-17 signaling pathway in an animal model of acute RRV disease. We also highlight that inhibiting the IL-17A/F heterodimer using a monoclonal antibody reduced disease severity and inflammatory responses, indicating that both isoforms of IL-17 may play a role in RRV disease pathogenesis, and targeting IL-17 is a potential effective therapeutic strategy in RRV patients. We also highlight that the stromal compartment plays a major role in alphavirus infection and identify multiple stromal populations in the joint and muscle using a novel organotypic cell culture model which can also be used in future high-throughput studies to test potential treatment strategies.