Arteriolar C4d in IgA Nephropathy: A Cohort Study

Abstract Rationale & objective Glomerular C4d (C4dG) as an indicator of lectin pathway of complement activation in IgA nephropathy (IgAN) has been associated with more severe kidney damage. Recent studies have suggested that vascular lesions in IgAN biopsies with complement deposition are also associated with disease progression. We aimed to study the clinical significance of arteriolar C4d (C4dA) in IgAN kidney biopsy tissue. Study Design Retrospective Cohort Study. Setting & participants Kidney biopsies from 126 adults diagnosed with IgAN under the Oxford Classification were stained using immunohistochemistry and classified according to glomerular and arteriolar C4d deposition. Additionally, vascular lesions including acute and chronic microangiopathy, arteriolar hyalinosis, and arterial intima fibrosis, were characterized. Predictors C4dA. Outcomes Progressive kidney disease defined as the decline in eGFR by ≥50% or occurrence of kidney failure with replacement therapy. Analytical Approach The association of C4dA and C4dG with baseline clinical and histological characteristics, as well as progressive kidney disease, were assessed with survival analysis using multivariable Cox regression analysis. Results C4dA was identified in 21 (17%) patients and was associated with mean arterial pressure (MAP), arterial intima fibrosis, and chronic microangiopathy. C4dA was also significantly associated with C4dG and both were associated with progressive kidney disease. In regression analysis, C4dA remained significantly associated with progressive kidney disease after adjusting for other significant predictors including baseline eGFR, MAP, and the presence of crescents. Limitations Findings based on the retrospective evaluation of a single-center's experience, limited number of events, a small number of patients with a broad range of kidney disease stages, and use of immunohistochemistry rather than immunofluorescence to detect C4d. Conclusions C4dA is a potential biomarker for disease progression in IgAN. It should be further investigated in larger cohorts to determine the value of C4dA in improving prediction of IgAN disease progression.