Virus-Induced Loss of Tolerance Against IgG as a Driving Force in Rheumatoid Arthritis

Rheumatoid arthritis (RA), an incurable inflammatory arthritis that causes pain, disability, and early mortality, often seems to suddenly appear, but actually immune tolerance is lost over many years preceding clinical disease during a time period termed "pre-RA." Although variability exists among individuals, anti-citrullinated protein antibodies (ACPAs) often develop decades prior to RA and rheumatoid factor (RF, Ig that bind to IgG Fc) rises several years prior. Interestingly, ACPAs are often multi-reactive with epitopes bound expanding around when RFs rise. Although RFs are also cross-reactive, they are known to bind two conformational IgG epitopes. Both RFs and ACPAs develop in ~70% of RA patients, but while ACPAs are >95% specific for RA, RFs also rise in 10%-20% of people with other causes of inflammation. We recently discovered new linear citrullinated IgG epitopes bound by IgG in RA but not other RF-producing conditions, which (1) identifies unique IgG epitopes bound in RA and (2) positions IgG as a shared, and potentially foundational antigen that could drive the generation of the RF and ACPA repertoires via epitope spreading. However, the stimuli for tolerance loss for IgG in RA remain a mystery. Viral infection can induce RFs and has long been hypothesized to be a RA trigger, but testing this hypothesis has been limited by a lack of unique biomarkers for immune activation by viruses as well as uniform post-viral patient cohorts for prospective evaluation. However, there is a critical need to define the steps and triggers of tolerance loss in RA. Without doing so, it will be impossible to intelligently design interventions to prevent RA as well as identify those who would most benefit from such interventions. We recently found that ~45% of COVID-19 patients generate RFs that bind novel linear IgG epitopes not bound in RA. Thus, the COVID-19 pandemic provides both a unique opportunity to study virus-induced loss of tolerance and, given the >500 million people infected with SARS-CoV-2, an urgent need to determine if and how viruses could drive RA. Indeed, some post-COVID-19 patients may already be close to RA, such as long COVID patients with joint pain. The overall goal of this proposal is to identify a foundational stimulus and antigen that could drive tolerance loss in RA, thereby addressing the Fiscal Year 2022 (FY22) Peer Reviewed Medical Research Program (PRMRP) Strategic Goal to identify factors impacting the onset and progression of associated immune-mediated diseases in the Rheumatoid Arthritis Topic Area and Autoimmune Disorders and Immunology Portfolio. We hypothesize that virus-induced loss of tolerance for IgG is a key part of RA development. To test this hypothesis, we take the innovative approach of using our novel IgG epitopes bound uniquely in COVID-19 or RA as biomarkers and a uniform post-COVID-19 cohort to identify a role for virus-induced tolerance loss for IgG in RA. In Aim 1, we will determine if virus-induced RFs could be an initial trigger for ACPAs in some RA subjects by quantifying conventionally detected RFs (cRFs), viral RFs, RA RFs, and ACPAs in sera collected at multiple points over 4 years post-COVID-19. In Aim 2, we will determine if virus-induced RFs could trigger ACPA expansion and cRFs in some RA subjects by quantifying viral RFs, RA RFs, cRFs and ACPAs in RA subjects for whom sera was longitudinally collected for decades prior to clinical RA. In Aim 3, we will determine if the loss of tolerance seen in pre-RA is present in long COVID by evaluating viral RFs, RA RFs, cRFs, and ACPAs in Veterans with long COVID with arthralgia. We expect to show that in some post-COVID-19 subjects, viral RFs will fall followed by a rise in RA RFs and ACPAs and that in some ACPA+ pre-RA subjects, viral RFs then RA RFs will precede ACPA expansion, suggesting that viruses could drive loss of tolerance for IgG, triggering other autoantibodies and RA. Moreover, we expect to detect RFs and ACPAs in long COVID, suggesting that a subset of long COVID is pre-RA. In the short term, the successful completion of this project will provide new insights into how tolerance is lost in RA, creating theoretical groundwork and preliminary data for future research that will evaluate virus-induced loss of tolerance in larger cohorts and following different viruses. Also, demonstrating that some long COVID patients have pre-RA will address a second Strategic Goal (Improve understanding of long-term complications of infections (e.g., long COVID) in the Viral Diseases Topic Area in the Infectious Diseases Portfolio) as well as open new horizons in long COVID treatment incorporating anti-RA drugs. Finally, in the long term, the viral and RA RFs that we will detect at key points prior to clinical RA can be leveraged to design biomarkers in pre-RA (addressing the Strategic Goal to identify biomarkers to predict onset and/or progression of associated immune-mediated diseases) as well as inform the design of interventions to prevent RA with its pain, mortality, and financial burdens, thereby improving the health of Service Members, Veterans, military beneficiaries, and the American public. Less