Identification of FH, FI and C4BP autoantibody positive patients. Plasma samples of LA+, SLE, RA, aHUS patients and healthy controls were analyzed for binding of IgG autoantibodies on immobilized purified FH (A-D), recombinant FI (E) or recombinant C4BP (F) using ELISA. FH-autoantibody titers for individual SLE patients characterized by presence of FH-autoantibodies divided according to SLEDAI score indicating low and high disease activity for the same patients are shown in Figure 1D. Values obtained for the same patient are connected by lines. The samples with levels above the mean plus 2 SD of those in the matched control group were considered positive. The dotted lines represent cut-offs calculated separately for each control group. Statistical significance of differences between autoantibody titers in diseases groups compared with controls was calculated using a Kruskal-Wallis test or Mann-Whitney test. P-values lower than 0.05 were considered statistically significant. ** P < 0.01; *** P < 0.001, ns not significant.