Antibody-mediated complement deposition was measured as previously described (26 (link)). PLL-conjugated polysaccharides for serotypes 3, 6A, and 19 was biotinylated and coupled to 1-μm fluorescent neutravidin beads. Ten microliters of a 1:100 bead suspension was opsonized with 10 μl of serum diluted 1:5 in PBS for 2 hours at 37°C in 96-well plates. Lyophilized guinea pig complement (Cedarlane) was resuspended in ice-cold water and then diluted 1:50 in veronal buffer with 0.1% gelatin (Boston BioProducts) added. Diluted complement (200 μl) was added to the opsonized beads and incubated for 20 min at 37°C. Beads were then washed with 15 mM EDTA in PBS and stained with fluorescein-conjugated anti-guinea pig complement component C3 at 30 μg/ml (MP Biomedicals, catalog no. 855385). Samples were washed and analyzed on the iQue Screener PLUS (Intellicyt). MFI of each sample was used as complement score. Each sample was assayed in three independent technical replicates performed on different days, and replicates were averaged. Specificity was confirmed using relevant control monoclonal antibodies for each serotype.