The alternative pathway of complement activation may be involved in the renal damage of human anti-glomerular basement membrane disease

Abstract

Linear deposition of IgG and complement 3 (C3) along glomerular basement membrane (GBM) is generally revealed in the kidneys of human anti-GBM disease. Our recent studies demonstrated the pathogenic role of complement activation in renal damage of this disease. However, the pathways of complement activation were still paradoxical. In this study, renal biopsy tissues from 10 patients with anti-GBM disease were used to investigate the pathways of complement activation by detecting the deposition of various complement components, including C1q, factor B, factor P (properdin), mannose-binding lectin (MBL), C3d, C4d and C5b-9, using immunohistochemistry and immunofluorescence. We found that C1q, factor B, properdin, C3d, C4d and C5b-9 were detected in all the glomeruli of our patients, along GBM with a linear and/or granular staining pattern. Furthermore, C1q, factor B and properdin co-localized well with C5b-9. The properdin also co-localized well with C3d. However, the deposition of MBL was diffusive in mesangium, GBM, Bowman's capsule and within crescents and was not co-localized with C5b-9 but partially co-localized with C4d. The intensity of factor B deposition (3.3 vs. 1.2, P<0.001) and C5b-9 deposition (3.2 vs. 1.6, P<0.001) was significantly stronger in the glomeruli with crescent formation, compared with the glomeruli without crescents. The complement system is overall activated via both the alternative pathway and classical pathway in the kidneys of human anti-GBM disease. The alternative pathway might play an important role in complement activation induced renal damage.

Figure 1. Complement components C5b-9, C3d, C4d, C1q and factor B were detected on paraffin sections of renal tissues from patients with anti-GBM disease by immunohistochemistry (magnification ×400).

A: C5b-9 linear deposition along the glomerular capillary wall (Patient #7); B: C3d linear deposition along the capillary wall (Patient #2); C: C4d linear deposition along the capillary wall (Patient #5); D: C1q linear deposition along the capillary wall (Patient #1); E: factor B linear deposition along the capillary wall (Patient #7); F: all the complement components above were negative in the renal tissues from patients with minimal change disease.

Figure 2. Complement components MBL and properdin were detected on frozen renal tissues from patients with anti-GBM disease by immunofluorescence (magnification ×400).

A: MBL diffusive granular deposition on the glomerular capillary wall, mesangial region and crescent in the glomeruli (Patient #4); B: properdin linear deposition along the capillary wall (Patient #10); C: MBL were negative in the renal tissues from patients with minimal change disease; D: Properdin was negative in the renal tissues from patients with minimal change disease.

Figure 3. Co-localization of various complement components were detected in frozen sections by immunofluorescence using laser confocal microscopy (magnification ×400).

A: IgG linear deposition along the glomerular capillary wall; B: C3d granular deposition along the glomerular capillary wall in the same section; C: IgG and C3d co-localized completely; D: C1q linear deposition along the glomerular capillary wall; E: C5b-9 granular deposition along the glomerular capillary wall in the same section; F: C1q and C5b-9 co-localized completely; G: factor B linear deposition along the glomerular capillary wall; H: C5b-9 granular deposition along the glomerular capillary wall in the same section; I: factor B and C5b-9 co-localized completely; J: properdin linear deposition along the glomerular capillary wall; K: C5b-9 granular deposition along the glomerular capillary wall in the same section; L: properdin and C5b-9 co-localized completely; M: properdin linear deposition along the glomerular capillary wall; N: C3d granular deposition along the glomerular capillary wall in the same section; O: properdin and C3d co-localized completely; P: MBL diffusive deposition; Q: C5b-9 granular deposition along the glomerular capillary wall in the same section; R: MBL and C5b-9 could not co-localize; S: MBL diffusive deposition; T: C4d granular deposition along the glomerular capillary wall in the same section; U: MBL and C4d partially co-localized along the glomerular capillary wall.