FIG 4.

Size distribution of ICs formed with a series of Ab concentrations. ICs were formed by mixing 2 × 10⁴ PFU of S221 with 0 to 200 μg of 4G2 Ab and subjected to analysis by dynamic light scattering (DLS), which detects the distribution of particle sizes and the ratio of molecules in solution. Size distributions of the major molecules in the solution were plotted by number (A) and by intensity (B). Abs and virus-Ab complexes have a diameter of ∼10 nm and ∼60 nm, respectively. Free Ab is detected at >2 μg IC, indicating that the ratio of free Ab to virus-Ab immune complex is very high. (C) The relative infectivity of the ICs in BHK-21 cells. Error bars indicate standard deviations from duplicate samples. An asterisk (*) shows the samples for which the ratio of Ab to virus-Ab complex is in far excess, as detected by DLS.