FIG. 2.

Neuraminidase treatment or low-pH treatment of HAE infections restores viral titer for the site I/site II HN variants.

(a) HAE cultures were infected with wt HPIV3 or with HN variant T193A, H552Q, or N551D. At each indicated day postinfection (x axis), each culture was treated with neuraminidase via the apical surface prior to the collection of supernatant fluid, and the number of infectious particles released (y axis) was determined by plaque assay. Data points are means (± standard deviations) of triplicate measurements and are representative of three to five experiments.

(b) Comparison of viral titers on day 3 with and without neuraminidase treatment.

(c) Quantification of the increase in day 3 viral titers with neuraminidase treatment.

(d) HAE cultures were infected with wt HPIV3 or with the HN T193A, H552Q, or N551D variant. On postinfection days 1, 2, and 3, medium at pH 5.0 or 7.0 (mock) was added to the apical surface 30 min before the collection of the supernatant fluid. The number of infectious particles released on day 3 (y axis) was determined by plaque assay. Data points are means (± standard deviations) of triplicate measurements and are representative of data from three experiments.