Abstract
We explored the potential link between chronic inflammatory arthritis and COVID-19 pathogenic and resolving macrophage pathways and their role in COVID-19 pathogenesis. We found that bronchoalveolar lavage fluid (BALF) macrophage clusters FCN1+ and FCN1+SPP1+ predominant in severe COVID-19 were transcriptionally related to synovial tissue macrophage (STM) clusters CD48hiS100A12+ and CD48+SPP1+ that drive rheumatoid arthritis (RA) synovitis. BALF macrophage cluster FABP4+ predominant in healthy lung was transcriptionally related to STM cluster TREM2+ that governs resolution of synovitis in RA remission. Plasma concentrations of SPP1 and S100A12 (key products of macrophage clusters shared with active RA) were high in severe COVID-19 and predicted the need for Intensive Care Unit transfer, and they remained high in the post–COVID-19 stage. High plasma levels of SPP1 were unique to severe COVID-19 when compared with other causes of severe pneumonia, and IHC localized SPP1+ macrophages in the alveoli of COVID-19 lung. Investigation into SPP1 mechanisms of action revealed that it drives proinflammatory activation of CD14+ monocytes and development of PD-L1+ neutrophils, both hallmarks of severe COVID-19. In summary, COVID-19 pneumonitis appears driven by similar pathogenic myeloid cell pathways as those in RA, and their mediators such as SPP1 might be an upstream activator of the aberrant innate response in severe COVID-19 and predictive of disease trajectory including post–COVID-19 pathology.
Highlights
The severity of acute COVID-19 is attributable to genetics, immune dysregulation, abnormal blood clotting and tissue disruption, implicating aberrant proinflammatory and antiviral innate immunity [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
We found that bronchoalveolar lavage fluid (BALF) macrophage clusters FCN1+ and FCN1+SPP1+ predominant in severe COVID-19 were transcriptionally related to synovial tissue macrophage (STM) clusters CD48hiS100A12+ and CD48+SPP1+ that drive rheumatoid arthritis (RA) synovitis
COVID-19 pneumonitis appears driven by similar pathogenic myeloid cell pathways as those in RA, and their mediators such as SPP1 might be an upstream activator of the aberrant innate response in severe COVID-19 and predictive of disease trajectory including post–COVID-19 pathology
Summary
The severity of acute COVID-19 is attributable to genetics, immune dysregulation, abnormal blood clotting and tissue disruption, implicating aberrant proinflammatory and antiviral innate immunity [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. SARS-CoV-2 infection is associated with emergence of polyarthritis, or flares of synovitis in RA patients in sustained disease remission, suggesting shared mechanisms of pathogenesis. Emerging data suggest that similar aberrant activation of myeloid cells in the blood [7, 20,21,22,23] and lung [24, 25] contribute to acute COVID-19 severity. The immune mechanisms of long-lasting clinical sequelae [26] described in convalescent COVID-19 patients are unresolved, hindering development of effective treatments and biomarkers of disease trajectory
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