SUN-039 URINARY ALPHA-M SUBUNIT OF INTEGRIN MAC-1 REFLECTS HISTOLOGICAL DISEASE ACTIVITY IN LUPUS NEPHRITIS

Abstract

Immunological mechanisms are indispensable for the onset and progress of glmerulonephritis; in particular, neutrophils and macrophages play a central role in acute glomerular inflammation. Their detection in kidneys from patients with LN is associated with disease activation and poor renal prognosis. Integrin Mac-1 comprising a unique α subunit (αm; CD11b) complexed with a common β2 subunit (CD18), and CD16b recognizing pathogenic IgGs are released from specific leukocyte subsets upon cell activation under inflammatory conditions including glomerulonephritis. This study aimed to investigate the association of urinary CD11b (U-CD11b) and CD16b (U-CD16b) with the histopathological activity of various glomerular diseases, particularly lupus nephritis (LN). Biological samples from 272 patients with glomerular diseases including 118 LN between 2008 and 2014 in Nagoya University (N-KDR cohort), and 44 LN patients including 15 longitudinal samples from the independent another LN population (Gunma/Saitama cohort) were subjected to the analysis. Urinary concentrations of U-CD11b, U-CD16b, hemoglobin scavenger receptor CD163 (U-CD163), and MCP-1 (U-MCP-1) were measured by ELISA. On renal LN specimens obtained from N-KDR cohort, glomerular CD11b+cells for neutrophils and monocytes/macrophages, and histological disease activity according to the biopsy activity index (BAI) were histologically evaluated. Receiver operating characteristic (ROC) curves for U-CD11b and U-CD16b to predict ISN/RPS class III/IV LN were also generated. To further corroborate the clinical findings and identify the specific timing of U-CD11b elevation after disease initiation, a murine model of antibody-mediated glomerulonephritis was induced by rabbit anti-mouse nephrotoxic serum in male C57BL/6J mice (NTS-GN). Among various forms of glomerular diseases including IgA nephropathy, minimal change nephrotic syndrome, membranous nephropathy, diabetic nephropathy, ANCA-associated vasculitis (AAV) and LN, U-CD11b and U-CD16b levels were significantly increased in LN patients from N-KDR cohort (U-CD11b/U-Cr; 36.2±50.4 ng/mg, U-CD16b/U-Cr; 2159 ± 2483 ng/mg), particularly in International Society of Nephrology/Renal Pathology Society (ISN/RPS) class III and IV. The significant U-CD11b elevations in class III and IV LN were further validated in collected samples from Gunma/Saitama cohort, and were decreased in the 15 longitudinal samples after the immunosuppressive therapy. In LN patients, U-CD11b, but not U-CD16b, was markedly correlated with the number of glomerular leukocytes and histopathological activity. Receiver operating characteristic curve analysis predicting proliferative LN revealed a superior level of U-CD11b (the area under the curve of U-CD11b/U-Cr: 0.916; cut-off: 24.0 ng/mg; sensitivity: 93.3%; specificity:84.1%) to those of CD16b, the scavenger receptor CD163, and monocyte chemotactic protein-1. In anti-mouse nephrotoxic serum glomerulonephritis, U-CD11b elevation was significantly correlated with renal damage and was reduced by corticosteroid treatment, as in human patients. Our results collectively suggest that U-CD11b is a useful biomarker for estimating the histopathological activity, particularly glomerular leukocyte accumulation, in LN.