Variation of Interferon Yield with Multiplicity of Infection

Abstract

CHIKUNGUNYA virus is one of the best inducers of interferon in chick cells, and many of the conditions which affect the yield of interferon have been elucidated^1,2. This communication reports an investigation of the relationship between the amount of Chikungunya virus inoculated into chick cell cultures and the subsequent yield of interferon. Dilutions of Chikungunya virus were prepared and placed in bottle cultures of chick cells which were then placed at 37° for 24 h. Supernatant fluids were collected, heated at 65° for 30 min to inactivate the virus, and assayed for interferon using the procedure of Linden-mann and Gifford³. The PDD₅₀, defined as the amount of interferon preparation required to depress the plaque count to 50 per cent of the control value³, was determined and plotted against the logarithm of the ratio of plaque-forming units/cell (Fig. 1). Less interferon was found to be produced by the cultures which received the greatest amount of virus than by those which were infected with approximately 0.1 plaque-forming units/cell. Even with 0.01 plaque-forming units/cell a considerable amount of interferon was produced. Three experiments have all given similar results. In other experiments fresh medium was placed on interferon producing cultures 24 h after infection and re-incubated for an additional 24 h. The amount of interferon found was usually less than 15 per cent of the first 24-h yield, indicating that most of the interferon was produced in the first 24 h after infection.