The Clinical Impact of Glomerular Immunoglobulin M Deposition in Patients with Type 2 Diabetic Nephropathy

Background: Glomerular immunoglobulin M (IgM) deposition is common in diabetic kidney disease. The clinical implication of IgM deposition in the renal tissues of type 2 diabetes mellitus patients with biopsy-proven diabetic nephropathy remains unclear. Materials and Methds: One hundred thirty-two patients with type 2 diabetes and biopsy-proven pure diabetic nephropathy were enrolled retrospectively. Clinicopathological features and renal outcomes were compared between patients with and without glomerular capillary IgM deposition. A Cox proportional hazards model was employed to identify the risk factors associated with renal survival. Results: Fifty-two patients had positive linear glomerular capillary IgM staining. Patients with glomerular capillary IgM deposition presented with heavier proteinuria, and lower serum albumin. During 35.5 (12, 107) months of follow-up, patients with glomerular tuft IgM deposition had shorter renal survival than those with negative IgM deposition (39 [23.74, 54.26] versus (vs.) 64 [45.82, 82.18] months, P = 0.01). Patients with glomerular complement 1q (C1q) deposition showed worse renal survival than those lacking glomerular C1q deposition (36 [23.82, 48.18] vs. 60 [50.27, 69.74] months, P = 0.001). Worse renal outcome was observed in patients with glomerular C3 deposition than in those without glomerular C3 deposition (37 [22.43, 51.56] vs. 63 [51.75, 74.25] months, P = 0.001). Multivariate Cox proportional analysis demonstrated that combined glomerular capillary IgM and C1q deposition was an independent predictor of end-stage renal disease (hazard ratio 3.75, 95% CI [1.68,8.35], P = 0.001). Conclusions: Patients with diabetic nephropathy and combined glomerular capillary IgM and C1q deposition had unfavorable renal outcome, which indicates that IgM derived from B cells might be involved in diabetic kidney injury.