FIG. 4.

Lysates from MDCK but not 293T cells activate 1918 HA-driven viral entry. Pseudotypes bearing the 1918 influenza virus HA, NA, and M2, or VSV-G were pretreated with trypsin and, subsequently, soybean trypsin inhibitor or lysates from MDCK or 293T cells. After 30 min the treated pseudotypes were used for infection of 293T and Huh-7 cells. Three days after infection, luciferase activities in cellular lysates were determined. The results of a representative experiment performed in triplicate are shown and were confirmed in two separate experiments. Error bars indicate standard deviations. Statistical significance was calculated employing a two-tailed t test for independent samples. cps, counts per second.