a, To quantify lining density, tdTomato+ macrophages (red) were manually isolated from 3D reconstructions of optically cleared and LSFM-imaged Cx3cr1creR26-tdTomato knee joints (autofluorescence, grey; CD31, blue) using Imaris software. Isolated surfaces (yellow) were volume-rendered for tdTomato+ macrophages (red) and whole-area volume (green). Lining density was calculated from the ratio of whole-area volume to macrophage volume. An exemplary image of the same knee joint before and after isolation of lining macrophages is shown. Scale bars, 200 µm. b, Dynamic-contrast-enhanced magnetic resonance imaging (DCE-MRI) data analysis. The red line drawn in the sagittal T1-weighted image after administration of contrast agent marks the transverse plane used for T1-weighted DCE-MRI analysis. The DCE curve generated from the region of interest (synovial tissue) was normalized to the measurement time point after complete injection of contrast agent, and the time of measurements was converted to distinctive measurements. c, CLSM images of knee joints of Cx3cr1GFP mice injected with protein-G-purified and Alexa-Fluor-647-labelled K/BxN serum IgG (grey) at the indicated time points after IgG injection, determining the uptake of labelled IgG by macrophages (GFP, green; CD68, red) in the synovial tissue and the synovial lining (synovial cavity, sc). Scale bars, 10 µm. d, CLSM scan with higher magnification showing localization of labelled IgG (grey) inside the vacuoles of CD68+ (red) lining and interstitial synovial macrophages 24 h after injection. Scale bars, 10 µm. e, Clinical course of K/BxN STA in wild-type mice that were treated with an anti-GR1 antibody to deplete PMNs and inflammatory Ly6Chigh monocytes and a control antibody (LTF-2), one day before induction of STA. Mean ± s.e.m.; n = 5 per group. f, Histological CLSM analysis of lining morphology after anti-GR1 antibody-mediated neutrophil/monocyte depletion one day after induction of STA. Lining macrophages (tdTomato, red). Scale bars, 20 µm. g, Flow cytometry analysis of synovial macrophages and blood Ly6Chigh or Ly6Clow monocytes of Cx3cr1creiDTR mice and iDTR control mice one day and five days after two injections of DT (500 ng per mouse per day, i.p.). Mean ± s.e.m; For day 1: iDTR, n = 5; Cx3cr1creiDTR, n = 7; for day 5, n = 3 per group. Two-tailed Student’s t-test, ***P < 0.0001. h, Representative BFM images of the infiltration of PMNs (Ly6G, green) and neutrophil extracellular trap formation (filled arrowheads, DAPI, blue) within the synovial cavity of knee joints of Cx3cr1creiDTR (n = 3) and iDTR control (n = 3) mice 6 days after injection of DT and 24 h after induction of STA (CD68, red). Scale bars, 200 µm and for magnified view, 50 µm. i, Treatment scheme and clinical course of STA in Cx3cr1creiDTR and iDTR control mice that had received a unilateral local injection of DT (n = 7) and PBS (n = 7), respectively. P values calculated using two-tailed paired t-test, **P = 0.008. j, Clinical course of STA including AUC of the corresponding clinical index in C57BL/6 wild-type mice treated with C5C2 claudin peptidomimetics (3.5 µmol kg−1, i.v., n = 8) or scrambled C5C2 control peptide (C5C2scr; 3.5 µmol kg−1, i.v., n = 6) one day before and after the induction of STA. Data are mean ± s.e.m. Mann–Whitney U-test for clinical index with *P ≤ 0.05, and two-tailed Student’s t-test for AUC with **P = 0.0062. k, Normalized signal intensity curves of DCE-MRI of synovial tissue of knee joints over 90 measurements with intervals of 7 s at the indicated days after STA in C57BL/6 wild-type mice treated with C5C2 claudin peptidomimetics (3.5 µmol kg−1, i.v.) or vehicle one day before the induction of STA. Data are mean ± s.e.m. Day 0: vehicle, n = 10 knee joints; C5C2, n = 10 knee joints; day 1: vehicle, n = 9 knee joints; C5C2, n = 10 knee joints. P values for AUC were calculated using two-tailed Student’s t-test, *P = 0,0256. l, Flow cytometry of blood monocytes and neutrophils of LysMcreCD115DTR mice (n = 6) and CD115DTR control mice (n = 5) one day after two injections of DT (500 ng per mouse per day, i.p.). Mean ± s.e.m.; two-tailed Student’s t-test, *P = 0.0467, **P ≤ 0.0069, ***P = 0.0001. Source data