Fig 1: CD55 is packaged into RSV particles and increases thresholds for C3 opsonization.(A) Images of RSV particles with enzymatically labeled F and CD55 or CD46 labeled via fluorescent antibodies. Panels show representative images of virus released from wildtype (wt) A549 cells and CD55 or CD46 knockout (KO) cells, displayed at matching contrast levels. Scale bar = 5 μm. (B) Histograms showing distributions of antibody intensities per RSV particle for wt and KO cell lines. (C) Comparison of C3 deposition on viruses raised in wt cells (open circles) or CD55 KO cells (closed circles) using three different F-specific antibodies and a negative control. Black markers show average values across four biological replicates. Individual replicates are shown in gray. Connecting lines indicate samples that were prepared in parallel, using virus collected from separate batches of wt and CD55 KO cells. p-Values are determined using a paired-sample t-test. (D) Similar plot as in C, but for data obtained from CD46 KO cells. (E) Distributions of antibody and C3 intensities for serial dilutions of CR9501 IgG1. Panels in the top row show results for viruses from CD55 KO cells, while panels from the bottom row show results for viruses from wt cells. The region indicated by the dashed line represents the threshold for C3-positive particles. Percentages in the upper left corners indicate the percentage of C3-postiive particles. Data is combined from three biological replicates. (F) Data from E plotted as percentage C3-positive particles per condition. Bars indicate mean values and points show individual replicates. * indicates p < 0.05 calculated using a two-sample t-test. See also Figure 3—source data 1. Figure 3—source data 1.Matlab code and data for Figure 3.