FIG. 4.

Antibody response to type B virus in mice inoculated with chimeric HA viruses. (A) Mice (three/group) were intranasally inoculated with each virus (10³ TCID₅₀). Three weeks postinoculation, tracheonasal washes and serum samples were taken from mice and tested for anti-B virus-specific IgA (tracheonasal wash) and IgG (serum) antibodies in an ELISA. Absorbance values (optical density at 405 nm [OD₄₀₅]) are reported as means ± standard deviation (n = 3). (B) HI titers were also tested in serum samples. Each bar indicates the titer for an individual mouse infected with the indicated chimeric virus.