#3068 Fibrosis and CD-163+ macrophages: making a difference between MPO-AAV and PR3-AAV

Abstract Background and Aims Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a necrotizing vasculitis characterized by inflammation of small blood vessels, with the kidney being one of the most affected organs. Its pathogenesis is a complex, multifactorial process involving inflammation and fibrosis in which macrophages play a crucial role. Macrophages are plastic cells that can change their phenotype in response to their environment. Infiltration of CD163+ macrophages (anti-inflammatory) in the interstitium and glomeruli is observed in AAV patients. Clinical and demographic differences between PR3-AAV and MPO-AAV were observed. We observed that interstitial fibrosis (IFTA) is more pronounced in MPO-AAV than in PR3-AAV. We aimed to investigate the differences in CD163+ macrophage infiltration and interstitial fibrosis between PR3-AAV and MPO-AAV. Method Retrospective single-center study of 80 AAV patients (66 MPO-AAV and 14 PR3-AAV) diagnosed by renal biopsy with at least 1 year of follow-up. Clinical and laboratory variables, ANCA type and renal/patient survival were evaluated. 26 human kidney tissue samples (13 MPO-AAV and 13 PR3-AAV) were stained for CD163+ by immunohistochemistry and immunofluorescence, and trichrome-stained biopsy slides were used to measure the degree of fibrosis. Histomorphometric quantification was performed using MetaMorph® software in both cases. Data analysis was performed under standard conditions. Statistical significance was defined as P values less than 0.05. All P values were 2-sided. Results CD163+ macrophages infiltration in the interstitial space was greater in MPO-AAV than PR3-AAV with statistical significance (p 0.001), observing an average infiltration area of 0.333% in MPO-AAV than 0.116% in PR3-AAV. Furthermore, IFTA was higher at diagnosis in MPO-AAV (35.35%) than in PR3-AAV (31.21%) at the diagnosis with a p = 0.03. However, a correlation between IF and CD163+ macrophages infiltration was not possible to stablish. Conclusion We have observed an increased macrophage infiltrate with an anti-inflammatory and reparative phenotype that is higher at diagnosis in ANCAS-MPO compared to ANCAS-PR3, the same difference occurs with respect to interstitial fibrosis. Since the study population is small, no correlations between fibrosis and CD163 macrophage infiltration have yet been found.