Adsorption and penetration of enveloped and naked vaccinia virus particles.

The adsorption and penetration of intracellular naked vaccinia virus (INV) and extracellular enveloped vaccinia virus (EEV) were examined. The adsorption kinetics of INV and EEV were similar, but INV adsorption was found to be more sensitive to the adsorption environment than EEV. The PFU-to-particle ratio for the two virus particles indicated that EEV was approximately two times as infectious as INV. Kinetic studies at 37 degree C showed that EEV penetrated cells more rapidly than INV. Penetration of EEV was unaffected by incubation in phsophate-buffered saline, but was somewhat reduced by incubation at 22 degree C. In contrast, INV penetration was effectively eliminated by incubation in phosphate-buffered saline or by incubation at 22 degree C. In addition, INV but not EEV pentration was sensitive to treatment with sodium fluoride and cytochalasin. B. These results are discussed with regard to the mechanism of INV and EEV penetration.