Association of the presence and quantity of C4d with the severity of kidney injury and kidney longevity in patients with primary IgA nephropathy

Object and hypothesis: The aim of this study is to evaluate the correlation between the glomerular C4d stain status and demographic, clinical and histopathological findings of patients with primary IgA nephropathy. Lectin pathway of the complement system is thought to be activated in patients with C4d positive glomerular staining; in those patients severe renal injury and decreased renal longevity rate is probable. Methodology: 45 patients with age of 18 years or older who were evaluated and diagnosed as primary IgA nephropathy by Dokuz Eylul University School of Medicine (DEUTF) Department of Nephrology between January 2003 and December 2013 were included in this survey. 8 patients were excluded due to the lack of biopsy specimens. After patients were invited to the department, written informed consent was obtained for staining with C4d on previous kidney biopsy material and quantitave immunoglobulin assay and for using history of disease data. Files of patients were researched retrospectively. Kidney biopsies were analyzed for staining with C4d kit (Cell Marque ®; C4d SP91 monoclonal antibody). Based on glomerular C4d staining results patients were grouped (as positive/negative). Those groups were compared according to their demographic (patient age and sex), clinical (degree proteinuria, serum creatinine level, creatinine clearance, presence of macroscopic hematuria, presence of hypertension, use of immunosuppressive drugs, need for renal replacement therapy) and histopathological (C4d staining in glomerular and extraglomerular sites of kidney; Oxford classification system criteria; mesangial immunoglobulin depositions; presence of crescent formation) findings. Glomerular C4d staining was performed with immunohistochemistry using monoclonal antibody. For statistical analysis SPSS 16.0 was used; findings were evaluated as statistically significant if p value is to be found less than 0.05. For categorical data analysis Chi-square and Fisher's exact test, for analysis of variance Mann-Whitney U test and correlation analysis were used. Kaplan-Meier and Cox proportional hazards analyses were planned to be performed to evaluate the effect of glomerular C4d staining on renal survival. Results: Of patients who were between ages of 20 and 71, 11 were female and 26 were male. 16 of 37 patients were identified as C4d-positive, and 21 as C4d-negative. During median follow up of 24.3 months (minimum <3 months, maximum 120 months) keeping seperately two patients who needed renal replacement therapy at the moment of diagnosis, no patient was shown to progress to end-stage kidney failure, thus renal survival analysis couldn't have been performed. In glomerular C4d-positive group mean proteinuria was 2906 mg/day, and it was 1091 mg/day in negative patients (p=0.002). In negative group mean estimated glomerular filtration rate according to MDRD formula was 95 ml/min (normal reference values > 90 ml/min) and serum creatinine was 1,248 mg/dL (normal reference values: 0.51-0.95 mg/dL), while it was 54.87 ml/min (p=0.023) and 2.1 mg/dL (p=0.022) in positive group, respectively. Glomerular C4d positive staining was associated with higher blood pressure (p=0.022), lower glomerular filtration rate (p=0.023), more severe endocapillary hypercellularity (p<0.001), more severe tubular atrophy (p<0.01) and use of cyclophosphamide (p=0.024). Although average age was higher in C4d-positive group (45.6 in positive group, 37.1 in negative group, 40.78 in whole group), it was thought to be incidental. Mesangial IgM positivity was found to be concurrent with glomerular C4d staining, nephrotic range proteinuria and use of cyclophosphamide. No statisticaly significant association was found between glomerular C4d staining and crescent formation. Statistically significant correlation was realised between interlobular arterial C4d staining and cellular crescent formation (p=0.027) as between interlobular arterial C4d staining and endocapillary hypercellularity (p=0.014). Conclusions: Glomerular C4d deposition was found to be with more unfavorable histopathological and clinical findings at the time of diagnosis. Although crescent formation is associated with worse renal outcomes, a statistically significant correlation between glomerular C4d deposition couldn't have been demonstrated. It was shown that mesangial IgM deposition is concurrent with glomerular C4d deposition, more severe histologic grade and necessity for more agressive therapy. More patient series are needed to clarify the role of IgM in process. More patient series should also be analyzed to understand the importance of C4d depositions in extraglomerular sites.