Analysis of antifactor H binding by Western blotting. Purified factor H was run out on 10% SDS-PAGE and transferred to nitrocellulose. Strips of nitrocellulose were then incubated with sera collected from subjects and bound antibody detected as described in “Methods.” ECL Western blotting substrate was used to visualize bound antibody. The same secondary reagent and exposure times were used throughout. Sera from known factor H autoantibody–positive and –negative subjects were used to allow standardization across multiple experiments. The positive (+ve) and negative controls (−ve) are on adjacent strips on the same autorad film and are shown as representative control signals (black box). The factor H autoantibody patients (1-13) and 2 normal subjects, A and B, are shown. These data are from a collection of sequential experiments. Molecular weight markers are shown, and the data are representative of at least 3 independent experiments.