Figure 1. Glomerular C3b/iC3b/C3d deposition in MRL/lpr mice increases as the mice age.

(a) Schematic diagram of conversion of soluble C3 to C3 fragments. ^§ Regulators of complement activation: CR1 – complement receptor type 1; MCP – membrane co-factor protein. (b) Immunostaining of MRL/lpr kidneys for C3b/iC3b (middle panel) and C3d (bottom panel). No staining is seen when the anti-C3-FITC antibody is omitted (top panel, arrowheads point to glomeruli). (c) Quantification of relative fluorescence units (RFU) shows an increase in C3b/iC3b deposition in glomeruli of MRL/lpr kidneys with disease progression (from ages 8, 16 and 22 weeks; n = 3 mice per age group; RFU for each mouse is a mean RFU obtained from 10 randomly selected glomeruli; horizontal bars represent the mean RFU from the 3 mice in the respective age groups; the R² and p values for the correlation of RFU with age are shown and were derived from linear regression analysis). (d) Quantification of RFU shows changes in C3d deposition in glomeruli of MRL/lpr kidneys with disease progression (ages 8, 16 and 22 weeks; n = 3 mice per age group; RFU for each mouse is a mean RFU obtained from 10 randomly selected glomeruli; horizontal bars represent the mean RFU from the 3 mice in the respective age groups). Although C3d fragment is present in larger C3b/iC3b moieties, the anti-C3d antibody likely did not cross-react with these larger moieties. This is evident from the discrepancy in the pattern of staining (punctate for C3b/iC3b versus ribbon-like for C3d) and unparalleled changes in intensity between C3b/iC3b and C3d on the MRL/lpr glomeruli from 16 to 22 weeks. Scale bar in (b) = 200 μm.