Plaque Formation and Initial Virus-Cell Interaction of Measles Virus

Abstract

The Sugiyama strain of measles virus adapted to FL cells produces plaques heterogeneous in size and morphology on FL and other stable human cell line monolayers making it difficult to assay by the plaque technique. A virus clone producing homogeneous clear plaques was established by repeated cloning of the strain. A practical reliable plaque assay method was established for this cloned line. FL cells were found to be well suited for this purpose, but Vero cells, a stable line of African green monkey kidney cells, were shown to be more sensitive than FL cells. HeLa cells could be used for the assay, but were less sensitive than the Vero or FL cell line. The initial step of measles virus adsorption onto host cells was shown to be reversible, dependent on electrolytes and almost temperature-independent, strongly suggesting adsorption is electrostatic in nature. At 36 C the initial stage of adsorption quickly passed into the next irreversible stage involving a temperature-dependent reaction; virus adsorbed at 36 C soon became resistant to the action of measles antibody, whereas little virus adsorbed at 4 C or 12 C became antibody-resistant. The time required for the adsorbed virus to move into the irreversible, antibody-resistant stage seems very short.