Complement Activation in Patients With Diabetic Nephropathy

Abstract

Introduction: Complement activation plays a role in various organs in patients with diabetes. However, in diabetic nephropathy (DN), the role of complement activation is poorly understood. We examined the prevalence and clinical significance of complement deposits in the renal tissue of cases with type 1 and type 2 diabetes with and without DN.

Methods: We measured the prevalence of glomerular C4d, C1q, mannose-binding lectin (MBL), and C5b-9 deposits in 101 autopsied diabetic cases with DN, 59 autopsied diabetic cases without DN, and 41 autopsied cases without diabetes or kidney disease. The presence of complement deposits was scored by researchers who were blinded with respect to the clinical and histological data.

Results: C4d deposits were more prevalent in cases with DN than in cases without DN in both the glomeruli (46% vs. 26%) and the arterioles (28% vs. 12%). C1q deposits were also increased in the glomerular hili (77% vs. 55%) and arterioles (33% vs.14%), and were correlated with DN (P < 0.01). MBL deposits were only rarely observed. C5b-9 deposits were more prevalent in the cases with diabetes mellitus (DM) than in the cases without DM (69% vs. 32%; P < 0.001). Finally, glomerular C4d and C5b-9 deposits were correlated with the severity of DN (ρ = 0.341 and 0.259, respectively; P < 0.001).

Conclusion: Complement activation is correlated with both the presence and severity of DN, suggesting that the complement system is involved in the development of renal pathology in patients with diabetes and is a promising target for inhibiting and/or preventing DN in these patients.

Keywords: C4d; complement activation; diabetic nephropathy; histological lesions; renal pathology.

Figure 1

Prevalence of C4d deposits in cases and controls. The percentage of cases and controls with complement factor C4d is shown for the indicated renal structures. Asterisks represent the overall differences among the nondiabetic controls, the diabetic cases without diabetic nephropathy (DN), and the diabetic cases with DN. The P values shown between the 2 groups represent post hoc analyses. **P < 0.01 and ***P < 0.001.

Figure 2

(a–c) Prevalence of mannose-binding lection (MBL), C1q, and C5b-9 deposits in cases and controls. The percentage of cases and controls with complement factor MBL (a), C1q (b), and/or C5b-9 (c) is shown for the indicated renal structures. The P values shown between the 2 groups represent post hoc analyses. ***P < 0.001, χ² test between nondiabetic controls, diabetic cases without diabetes nephropathy (DN), and diabetic cases with DN.

Figure 3

Representative images of complement staining in patients. Kidney sections were immunostained for the indicated proteins, and representative images containing the glomeruli, glomerular hili, arterioles, and arterial branches are shown. Mannose-binding lection (MBL) staining was negative in the glomerular hilus, arterioles, and arterial branches. Bars = 50 μm.

Figure 4

Percentage of patients with glomerular C4d deposits and glomerular C5b-9 deposits plotted against diabetic nephropathy class. The presence of glomerular C4d (a) and C5b-9 (b) was correlated with diabetic nephropathy class. For C4d and C5b-9, the Spearman rank correlation coefficient (ρ) was 0.344 and 0.228, respectively (both P < 0.01). Cases without diabetic nephropathy were classified as class 0.

Figure 5

Percentage of renal sections containing IgM, C1q, mannose-binding lectin (MBL), C4d, or C5b-9 deposits. Biopsy samples were obtained from living patients with diabetic nephropathy (n = 12) and healthy living renal transplantation donors (n = 10) and stained for IgM, C1q, MBL, C4d, and C5b-9. P values were calculated using the χ² test.

Figure 6

Glomerular IgM deposits co-localize with glomerular C1q and C4d. Adjacent sections of an autopsied kidney from a case with diabetic nephropathy were stained for C1q (a) or IgM (b). Adjacent sections of an autopsied kidney from a case with diabetic nephropathy were stained for C4d (c) or IgM (d); the arrowheads indicate co-localization between C4d and IgM. The scale bars in (a) and (c) represent 50 μm; the scale bars in (b) and (d) represent 25 μm.