Rheumatoid arthritis development : novel autoantibody- and cytokine-mediated mechanisms

The understanding of rheumatoid arthritis (RA) pathogenesis has advanced to a level that many individuals considered to be at risk for disease progression can be identified during the preclinical stages of RA. This screening relies on the presence of characteristic RA autoantibodies, namely anti-citrullinated protein antibodies (ACPAs), alongside other factors such as joint complaints. ACPAs are a biomarker with diagnostic value in RA, and at least two thirds of patients have increased ACPA concentrations in serum. These peculiar antibodies can also be found in circulation years before clinical RA, and they associate with a more erosive disease phenotype. Another group of autoantibodies with recent interest in RA are antibodies targeting malondialdehyde-acetaldehyde (MAA) protein modifications, which are also elevated in serum of RA patients. Similarly to ACPAs, anti-MAA antibodies can also be present in RA patient serum before disease onset. The role of different anti-modified protein autoantibodies (AMPAs) in the inflammatory processes taking place prior and during established RA is still not fully explained. Additionally, the factors mediating the progression from systemic autoimmunity defined by increased serum autoantibodies to RA remain to be elucidated. The work in this thesis aims to address some of these questions by investigating functional properties of monoclonal ACPA and anti-MAA antibodies, obtained from RA patients, and by analysing other serum soluble mediators in a cohort of individuals at-risk of RA. Our studies also relied on murine models of arthritis, in vitro cell cultures and RNA-sequencing techniques. We describe that monoclonal and polyclonal ACPAs have an anti-inflammatory capacity in a model of arthritis induced by passive transfer of arthritogenic antibodies. We confirmed that ACPAs do not bind resting neutrophils but will bind the intracellular content of neutrophils activated to undergo NETosis. Additionally, polyclonal ACPAs from different RA patients possess distinct NET-binding and pro-osteoclastogenic properties. We found that anti-MAA antibodies can transcriptionally rewire macrophages leading to a shift in their cytokine profile concurrent with a more pro-inflammatory phenotype. Lastly, we detected an increase of the chemokine CCL22 in serum from RA patients and individuals at-risk of RA, which was more abundant in those individuals that progressed to RA, in comparison with non- progressors. We describe a link between CCL22 and smoking, which is a known risk factor in RA, and confirm CCL22 expression in synovial tissue and synovial fluid, primarily in a subset of DCs expressing LAMP3, which argues for a role of CCL22 in synovial DC-T cell interactions. The studies included in this thesis thus contribute to understanding the complex role of autoantibodies in RA and motivate additional efforts in dissecting their effector functions, especially at the polyclonal level. Moreover, our studies highlight the relevance of previously undefined soluble mediators in RA pathogenesis and reinforce the importance of specific cellular communications in the RA synovium, which could be targeted by future therapeutic alternatives. List of scientific papers I. Divergent and dominant anti-inflammatory effects of patient- derived anticitrullinated protein antibodies (ACPA) in arthritis development. Raposo B, Afonso M, Israelsson L, Wähämaa H, Stålesen R, Wermeling F, Hensvold AH, Grönwall C, Rethi B, Klareskog L, Malmström V. Ann Rheum Dis. 2023; 82(5):724-726. https://doi.org/10.1136/ard-2022-22341 II. Anti-Citrullinated Protein Antibody Reactivity towards Neutrophil-Derived Antigens: Clonal Diversity and Inter- Individual Variation. Cîrciumaru A, Afonso MG, Wähamaa H, Krishnamurthy A, Hansson M, Mathsson-Alm L, Keszei M, Stålesen R, Ottosson L, de Vries C, Shelef MA, Malmström V, Klareskog L, Catrina AI, Grönwall C, Hensvold A, Réthi B. Biomolecules. 2023; 13(4):630. https://doi.org/10.3390/biom13040630 III. Macrophage activation and inflammatory priming by anti-MAA antibodies in rheumatoid arthritis. Afonso M, Sun J, Sakuraba K, Cîrciumaru A, Lagutkin D, Filipović M, Catrina AI, Grönwall C, Hensvold A, Réthi B. Clin Immunol. 2024; 265:110303. https://doi.org/10.1016/j.clim.2024.110303 IV. Increased CCL22 production in early rheumatoid arthritis development with potential impact on mucosal autoimmunity, joint inflammation and T cell recruitment to LAMP3+ dendritic cells Filipović M, Afonso M, Argyriou A, Cîrciumaru A, Joshua V, Ringh M, Grönwall C, Carlberg K, Chen SY, Dehara M, Krishnamurthy A, Vivar N, Wahamaa H, Ekstrom TJ, Wadsworth MH, Sharma RK, Askling J, Winkler A, Smith JE, Klareskog L, Catrina AI, Hensvold A, Malmström V, Chemin K, Réthi B. [Manuscript]