Incomplete influenza virus: partial functional complementation as revealed by hemadsorbing cell count test

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Abstract
In MDCK [Madin-Darby canine kidney] cells inoculated with an appropriate dilution of influenza virus, single hemadsorbing cells could be counted 8 h postinfection against a background of nonadsorbing cells. Standard virus preparation exhibited a linear relationship between the virus dilution and the number of hemadsorbing cells. With incomplete virus preparations obtained by passages of undiluted virus in chicken embryo, the dependence was nonlinear. A ts mutant (ts-29) of A/FPV/Weybridge (Hav1 Neq1) failed to convert MDCK cells into a hemadsorbing state at 42.degree. C. The ability of ts-29 to produce hemadsorbing cells could be rescued by incomplete wild-type virus. The capacity of incomplete virus for this partial functional complementation was inactivated by UV irradiation with 1-hit kinetics. The size of the target was about 5.5 times smaller than that of the virus genome. Thus at least some influenza virus genes in defective interfering particles are functional.