Effect of Ionic Strength on the Binding of Sindbis Virus to Chick Cells

Sindbis virus can adsorb to chicken embryo fibroblasts in two different ways. "Loosely" bound virus can be washed off the cell with buffers of ionic strength 0.2 or greater, whereas "tightly" bound virus remains attached under these conditions. When Sindbis virus is adsorbed to chick cells at 4 C from a buffer of ionic strength 0.17, 40 to 50% of the adsorbed virus is loosely bound, the remainder tightly bound. Infection of chick cells by Sindbis virus has only small effects on the total amount of virus that can be bound to the cells. However, the amount of Sindbis virus that can be tightly bound declines rapidly beginning at 2 to 3 h after infection. By 7 h after infection, the amount of virus that can be tightly bound is only 10 to 20% of the amount bound to uninfected cells. The adsorption (and penetration) of virus at 37 C is most efficient at an ionic strength of 0.15 to 0.17; at this ionic strength most of the adsorbed virus is tightly bound. At higher ionic strengths the virus adsorbs poorly. At lower ionic strengths most of the virus is loosely bound. A second enveloped virus, vesicular stomatitis virus, has been studied for the purposes of comparison; its adsorption behavior differs from that of Sindbis virus.