Figure 7. Induction of serum antibodies in response to infection of 1-day-old and 2-week-old chickens with parental and F protein cleavage site mutant APMV-4 viruses.

Chickens were inoculated with each virus (256 HA units) by the intranasal route in the same experiment as Table 2. Sera were collected at 14 dpi and evaluated for virus-specific antibodies by a hemagglutination inhibition assay using chicken erythrocytes.