PT - JOURNAL ARTICLE AU - Søren Andreas Just AU - Christian Nielsen AU - Jens Christian Werlinrud AU - Pia Veldt Larsen AU - Eva Kildall Hejbøl AU - Helene Broch Tenstad AU - Henrik Daa Schrøder AU - Torben Barington AU - Trine Torfing AU - Frances Humby AU - Hanne Lindegaard TI - Fibrocytes in early and long-standing rheumatoid arthritis: a 6-month trial with repeated synovial biopsy, imaging and lung function test AID - 10.1136/rmdopen-2020-001494 DP - 2021 Mar 01 TA - RMD Open PG - e001494 VI - 7 IP - 1 4099 - http://rmdopen.bmj.com/content/7/1/e001494.short 4100 - http://rmdopen.bmj.com/content/7/1/e001494.full SO - RMD Open2021 Mar 01; 7 AB - Objectives To correlate the level of fibrocytes in peripheral blood, synovial tissue and in vitro culture in rheumatoid arthritis (RA) with changes in disease activity, imaging and pulmonary function.Methods Twenty patients with early RA (ERA) and 20 patients with long-standing RA (LRA) were enrolled in a 6-month prospective study. Sixteen patients undergoing wrist arthroscopy were healthy controls. Patients with RA underwent pulmonary function tests, ultrasound and synovial ultrasound-guided needle biopsy of the same wrist at baseline and 6 months. Wrist MRI was performed at baseline (all) and 6 months (ERA). Circulating fibrocytes were measured by flow cytometry, in vitro by the number of monocytes that were differentiated to fibrocytes and in synovial biopsies by counting in histological sections.Results Fibrocytes were primarily located around vessels and in the subintimal area in the synovium. Fibrocyte levels did not decline during the trial despite effective RA treatment. In the ERA group, increased synovitis assessed by ultrasound was moderate and strongly correlated with an increase in circulating and synovial fibrocyte levels, respectively. Increased synovitis assessed by MRI during the trial in the ERA group was moderately correlated with both increased numbers of circulating and cultured fibrocytes. Absolute diffusion capacity level was overall weakly negatively correlated with the level of circulating and synovial fibrocytes. The decline in diffusion capacity during the trial was moderately correlated with increased levels of synovial fibrocytes.Conclusion Our findings suggest that fibrocytes are involved in RA pathogenesis, both in the synovium and the reduction in lung function seen in a part of patients with RA.Trial registration number NCT02652299.