Fig. 6.

IFN sensitivities of various influenza A virus strains in chicken tracheal organ cultures. Tracheal organ cultures (6 or 7 individual cultures for each experimental condition) kept in medium containing or lacking 1,000 U/ml of chicken IFN-α were infected with 100 PFU of R65-wt, R65-truncNS1, R65-PR8(123), and FPV Rostock or 1,000 PFU of WSN, R66, and Ont6118. Virus titers in individual culture supernatants were determined at the indicated times postinfection. Each dot represents the result of one individual culture. The origin of the y axis was set to the detection limit of the titrations.