Plaque-reduction neutralization assay showing the effect of B-virus incubation with anti-A/B–containing human serum.

B and H virus supernatants, diluted to 10³ PFU/mL, were incubated with a human O-type reference serum, lacking measles-specific Ab and previously diluted 1:5 in PBS. Similarly, diluted B and H virus supernatants were incubated with the same serum, previously decomplemented by heat-inactivation. Subsequently, virus/serum mixtures were analyzed for viral titers by a plaque-reduction neutralization assay on Vero cells. Results (mean SEM) in triplicates are shown as the mean percentages as compared to the untreated (PBS) B- and H-virus titers (100%).