Fig 8.

Pig respiratory epithelial cells released less infectious virus than did the corresponding human cells infected with HPAI H5N1 (A/turkey/Turkey/1/05) and USSR H1N1 (A/USSR/77) viruses. (A) Real-time PCR on 24-h-infected (MOI of 1) culture supernatants showed that the H5N1 M gene RNA level in pig cells was about 10-fold lower than in from human cells. USSR H1N1 virus M gene RNA was more abundant (2 to 3 orders of magnitude) than HPAI H5N1 virus M gene RNA for each mammalian species. Between human and pig cells, USSR H1N1 M gene RNA was more highly expressed in pig cells. Data shown are means of data from three biological replicates. (B) Supernatants of infected human and pig cells collected at 24 h and 48 h postinfection were used to infect MDCK cells for 6 h, followed by immunodetection for virus nucleoprotein. The number of infected MDCK cells per microliter of supernatant was determined. Representative fields of MDCK cells infected with supernatants from 48-h infections of human (i and iii) and pig (ii and iv) cells by HPAI H5N1 (i and ii) and USSR H1N1 (iii and iv) viruses are shown. Pig cells produced significantly less new infectious virus than human cells for both virus subtypes. Data points represent means of data from three biological replicates. Error bars indicate standard errors of the means. *, P < 0.05.