#4451 MONOCYTE MIGRATION AND ACTIVATION IN ANCA-ASSOCIATED GLOMERULONEPHRITIS

Abstract

Abstract Background and Aims Glomerular injury in Anti-Neutrophil Cytoplasmic Antibodies (ANCA)-associated glomerulonephritis (AGN) is associated with macrophage infiltration. To date, their role and origin remain to be fully elucidated. Activated blood monocytes likely transmigrate and differentiate into kidney macrophages depending on the local microenvironment. Even in remission, some studies indicate sustained monocyte activation and upregulation of adhesion markers. The aim of this study was to research the intrinsic migration capacity of monocytes in AGN. Targeting monocyte migration might open new therapeutic avenues in the treatment of AGN. Method Transendothelial migration of monocytes was tested in AGN patients with active disease (n = 2), in remission (n = 8) and healthy controls (n = 6). To assess their adhesive and migratory capacity, freshly isolated CD14 positive monocytes were added to confluent TNF-α or IL1β overnight-stimulated Human Aortic Endothelial Cell (HAEC) for 30 minutes and subsequently fixed. Monocyte adhesion and transmigration was visualized by phase-contrast microscopy and quantified using ImageJ. To unravel the potential mechanisms driving these differences in monocyte migration, we performed bulk RNA-sequencing of monocytes from AGN patients with active (n = 4) and stable (n = 10) disease, and healthy controls (HC) (n = 6). Results Monocyte adhesion, but not migration, was significantly increased during active disease, independently of the stimuli used to mimic the pro-inflammatory phenotype of endothelial cells (EC) (Figure 1). During remission, decreased adhesion was found on the IL1β-stimulated ECs. While CD11b mRNA expression was upregulated, CD11a expression was downregulated in monocytes from active AGN patients compared to HC. Two genes involved in paracellular monocyte transmigration (JAML, PECAM-1) were significantly decreased. Most AGN patients were treated with corticosteroids at time of experiments. Conclusion These results suggest a remarkable increase in monocyte adhesion, but lower intrinsic migration capacity, in a 30 minute time-frame during active AGN. Our findings on migration are surprising in the light of theorized enhanced monocyte extravasation towards diseased AGN kidneys. Therefore, it could be speculated that after a longer period of time, a subset of the adherent monocytes would ultimately migrate and differentiate into kidney macrophages. In remission, long-term immunosuppressive treatment or chronic inflammation might decrease monocyte adhesion. This was the first ex-vivo study to research monocyte migration in AGN, further research is required to validate findings and to develop new therapies targeting monocyte migration.