FIGURE 6.

Properdin and factor H have different binding requirements on HS/heparin. A, properdin (open circles) interacts dose-dependently with HSPG in solid phase ELISA, whereas factor H (closed circles) does not interact with HSPG. B, heparin-albumin is able to interact with both properdin (open circles) and factor H (closed circles) in ELISA. Optical density (OD) measured at 450 nm. C, binding of factor H (10 μg/ml) to coated heparin-albumin did not change with increased concentration of properdin. Preincubation of factor H (10 μg/ml) with various concentrations of properdin (open circles) and incubation of properdin, followed by washing and factor H (10 μg/ml) incubation (closed circles) did not interfere with factor H binding to heparin. D, properdin binding (10 μg/ml) to HK2 cells is not impaired by increasing concentrations of factor H on the cells. The error bars represent S.E. of duplicates. All the assays in A–D have been performed three or more times; the graphs shown here are representative examples.