LAUSR

Background: ANCA-associated vasculitis (AAV) causes necrotizing crescentic glomerulonephritis (NCGN) which is a major contributor to morbidity and mortality in AAV. Since therapy relies on cytotoxic agents with potentially severe adverse effects, a reliable non-invasive biomarker of disease activity is needed to determine the right balance between over- and undertreatment. Using the urine space as a window into the local inflammatory milieu of the kidney, quantification of urinary leukocytes using flow cytometry has become an upcoming marker of various other inflammatory kidney diseases. As recent studies have illuminated the emerging role of T regulatory (Treg) and Th17 cells in the pathogenesis of AAV, these could represent a viable non-invasive biomarker more closely displaying the underlying pathogenic processes than metabolites or epiphenomena of inflammation. Objectives: To quantify urinary T cells in active renal AAV and asses their biomarker characteristics. Methods: Using flow cytometry, T-lymphocytes and their subsets were quantified in peripheral blood and urine samples from patients with active AAV with or without NCGN, in stable remission with previous NCGN and healthy controls. Concentrations of urinary soluble metabolites and cytokines (Monocyte-attracting protein 1 (MCP-1), sCD163, sCD25 and C5a) were measured using Multiplex analysis. Results were verified in a separate validation cohort. Results: Patients with renal active AAV (n = 30) showed significantly higher urinary cell counts of total T cells, CD4+, CD8+, Treg and Th17 subsets than disease (n = 21) and healthy controls (n = 8). Patients with active renal AAV also showed a significantly higher percentage of Tregs in urine than in blood. While Tregs allowed a robust discrimination between active renal AAV and disease controls (receiver operator characteristics (ROC): area under the curve (AUC) 0.93, sensitivity 79%, specificity 95%) quantification of all T cells proved to be slightly more accurate (ROC: AUC 0.95, sensitivity 92%, specificity 95%). Soluble markers showed a slightly inferior discrimination (MCP-1 ROC: AUC 0.90, sensitivity 60%, specificity 100%, sCD163 ROC: AUC 0.92, sensitivity 96%, specificity 85%) while sCD25 and C5a were far less accurate. Conclusion: Urinary T cells are significantly elevated in active renal AAV and the increased frequency of Tregs in urine suggests active migration into inflamed glomeruli and thereby the urine rather than mere bleeding of ruptured capillaries. These cells show great potential for a non-invasive biomarker close to the local inflammatory milieu. Particularly the total count of urinary T cells showed slightly superior biomarker characteristics than previously established soluble markers. Further studies are needed to confirm these results and show potential prognostic value of these cellular markers. Disclosure of Interests: None declared