Effects of a neutralizing immune serum raised against serotype O on strong and weak IFN-α inducing FMDV serotype O isolates. IFN-α responses induced by various MOIs of FMDV O UKG 2001 (A) or O Bulgaria 1/91 (B) pre-incubated with anti-O Manisa immune serum at the indicated dilutions. Immune complexes were allowed to form by incubating at 39°C for 30 min, before addition to enriched pDC (CD14-depletion/CD172a-enrichment). After 24 h of culture, IFN-α was quantified by ELISA. The mean value of triplicates and standard deviations of triplicate cultures are shown. The data are representative of three independent experiments. The neutralization titres (NT) of the serum against the two viruses is expressed in log10 of serum dilution.