FIGURE 3.

Effect of heparin on Factor H recruitment by pneumococci. A, binding of FITC-heparin (2 μg) to pneumococci or to Factor H-pretreated pneumococci was determined by flow cytometry. The histogram shows the log fluorescence intensity (FITC-A) on the x axis, and the y axis shows the number of events. B, binding of heparin-pretreated Factor H to pneumococci. The effect of heparin on pneumococcal recruitment of Factor H was analyzed by flow cytometry after preincubation of 2 μg of purified Factor H with the indicated amounts of heparin per reaction. Bacterial bound Factor H was determined by flow cytometry, and results were expressed as mean fluorescence intensity multiplied with the percentage of FITC-labeled bacteria. The graph shows a representative experiment. The results are also represented as histograms, where the x axis represents fluorescence of pneumococcus-associated Factor H, in the absence (w/o) or presence of 50 units of heparin, on a log₁₀ scale, and the y axis represents the number of events.