chapter  3
14 Pages

Biological activities of interferon gamma

However, this is not always the case, because this activity depends on the cellular type and the viral strain used. For example, the antiviral action of IFN

γ

against the Sindbis virus is severalfold higher and its onset is faster than that of IFN

α

and

β

(Gomi et al. 1985). The specific antiviral activity of IFN

γ

is of the order of 10

to 5

×

IU/mg. When cells are exposed to this cytokine they become resistant to viral infections (Horisberger and de Staritzky 1985; Sedmak et al. 1985; Mistchenko et al. 1989). The combination of IFN

γ

and IFN

β

results in a synergistic antiviral activity (Gomi et al. 1986). The antiviral activity of interferons is determined experimentally by

using standard cell lines (most often the human cell line WISH) and a suitable virus (for example, the vesicular stomatitis virus, VSV) which has a cytopathic lethal effect on the cells. The cells are cultivated in a suitable nutritional medium. They are treated with interferon in different concentrations and are then infected with the virus. The effect of the interferon is measured

as the percentage of dead cells. The reciprocal value of the largest dilution that protects 50% of the cells from the cytopathic effect of the virus is accepted to give the concentration of interferon in international units (IU) in 1 ml.