Card9/neutrophil signalling axis promotes IL-17A-mediated ankylosing spondylitis

Abstract

ObjectivePolymorphisms in the antifungal signalling moleculeCARD9are associated with ankylosing spondylitis (AS). Here, we investigated the cellular mechanism by which CARD9 controls pathogenic Th17 responses and the onset of disease in both experimental murine AS and patients.MethodsExperiments in SKG, Card9−/−SKG, neutrophil-deplete SKG mice along within vitromurine, neutrophil and CD4+T cell cocultures examined Card9 function in neutrophil activation, Th17 induction and arthritis in experimental AS. In AS patients the neutrophil: Bath Ankylosing Spondylitis Functional Index relationship was analysed.In vitrostudies with autologous neutrophil: T cell cocultures examined endogenous CARD9 versus the AS-associated variant (rs4075515) of CARD9 in T cellular production of IL-17A.ResultsCard9 functioned downstream of Dectin-1 and was essential for induction of Th17 cells, arthritis and spondylitis in SKG mice. Card9 expression within T cells was dispensable for arthritis onset in SKG mice. Rather, Card9 expression controlled neutrophil function; and neutrophils in turn, were responsible for triggering Th17 expansion and disease in SKG mice. Mechanistically, cocultures of zymosan prestimulated neutrophils and SKG T cells revealed a direct cellular function for Card9 within neutrophils in the potentiation of IL-17 production by CD4+T cells on TCR-ligation. The clinical relevance of the neutrophil-Card9-coupled mechanism in Th17-mediated disease is supported by a similar observation in AS patients. Neutrophils from HLA-B27+AS patients expanded autologous Th17 cellsin vitro, and the AS-associated CARD9S12Nvariant increased IL-17A.ConclusionsThese data reveal a novel neutrophil-intrinsic role for Card9 in arthritogenic Th17 responses and AS pathogenesis. These data provide valuable utility in our future understanding of CARD9-specific mechanisms in spondyloarthritis .