Figure 2.

Timing of C3 opsonization of Klebsiella pneumoniae. Organisms were incubated with normal or variously depleted sera. Aliquots were removed at the time points shown, stained with FITC-labeled antihuman C3, and analyzed by flow cytometry. In normal human serum (upper series), C3 coverage was detectable within 2 minutes of exposure and was well underway by 8 minutes. Serum lacking classical pathway activity (by C1q depletion, middle series) showed delayed onset but similar coverage by the last measured time point. Serum lacking alternative pathway activity (by Factor B depletion, lower series) showed no progression of opsonization over time. Results are representative of three replicate studies and are scaled such that the area under each curve is equal to 1.0 (i.e., they are scaled as probability density functions).