Antibody binding to the surfaces of GAS. Sera from immunized BALB/c (A) and humanized plasminogen AlbPLG1 (B) mice raised against vaccine antigens (M1, Combo#5, J8-ADI, and ΔGAC-ADI) were incubated with live GAS pM1.200 and 5448, respectively. Specific binding to the bacterial surface was detected by a shift in Alexa Fluor 488 fluorescence. Representative histograms for test antigens are shown with a black solid line; histograms for PBS-immunized mice are shown as a shaded area. The populations in histograms for test antigens were statistically different (P < 0.01) from control histograms with T(X) values above the established cutoff value of T(X) = 100. T(X) values, shown on the right top corner of each panel, were determined by the probability binning algorithm in FlowJo.