Altered distribution of intraglomerular immune complexes in C3-deficient mice

Abstract

We have studied the role of complement in a model of glomerular inflammation induced by the in situ formation of immune complexes along the glomerular basement membrane. In C3-deficient mice, produced by homologous recombination, immune complex formation occurs initially in the subendothelial site and progresses slowly to the subepithelial position, whereas wild-type mice do not develop subendothelial deposits. In addition, the accumulation of electron-dense deposits is greater in the complement-deficient mice. Complement therefore influences glomerular handling of immune complexes, possibly because of changes in the physiochemical characteristics of the immune complexes. However, despite evidence of complement activation in the wild-type mice, as demonstrated by immunohistochemical detection of C3, C4 and C9, the degree of proteinuria was similar in C3-deficient mice. We conclude that, although complement is required for the normal glomerular metabolism of immune complexes, other, complement-independent, factors are involved in the generation of glomerular injury in this model.

Figure 1

Proteinuria. (a) Both wild-type and C3-deficient mice became proteinuric 4 days after the induction of the disease (group 1, n = 6–9 per group, mean±SEM). (b) There was no significant difference in 24-hr urinary albumin excretion at any time-point during the course of the disease (group 2, n = 9 per group mean±SEM).

Figure 2

Histological assessment. Periodic acid Schiff staining ( × 400 original magnification) demonstrating progressive glomerular damage in wild-type and C3-deficient mice on days 2 (a), 4 (b), 6 (c) and 10 (d). There is evidence of capillary wall thickening (arrowed) and mesangial expansion (arrowed) from day 4 onwards. By day 6 the glomeruli contained large vacuoles (arrowed) with progressive disruption of glomerular morphology.

Figure 3

Immunochemical analysis of immunoreactants. (a) shows the distribution of cBGG at days 2, 4, 6 and 10 in both the wild-type and C3-deficient mice (original magnification × 400). A similar distribution and intensity of staining is seen in both groups of animals. (b) shows the distribution of C3 staining in the wild-type mice at the above time points. C3 staining was absent in the C3-deficient mice.

Figure 4

Electron micrographs ( × 20 000) at day 2 (a), 4 (b) and 6 (c). Electron-dense deposits (arrows) are in a subepithelial position in wild-type mice at all time-points. C3-deficient mice initially show subendothelial deposits with transition to a subepithelial site as the disease progresses. Epithelial cell foot process effacement is evident from day 4 onwards.

Figure 5

Electron micrographs ( × 20 000) at day 10. Wild-type mice have discrete subepithelial deposits (a) whereas C3-deficient mice have intramembranous deposits (b) and have lengths of basement membrane with an almost continuous band of electron-dense material (c) which are not seen in the wild-type mice.