Enhancement of viral infectivity by cytochalasin

Abstract Cytochalasins B and D enhance the infectivity of poliovirus; a 5-fold increase in viral titer occurs on treatment of cells with 4–6 μg/ml of either congener. At lower concentrations, however, CD is more effective than CB in increasing the infectibility of cells. The enhancement of viral infectivity occurs whether CD is applied to the cells before and during viral attachment, or after penetration has occurred. CD does not affect the attachment, penetration, or elution of radiolabeled poliovirus, and only minimally stimulates uncoating. Enhancement of infectivity progressively declines as the time of addition of cytochalasin after viral penetration is prolonged. We conclude that cytochalasin affects some event(s) early in the eclipse period of polioviral development. Pretreatment of Vero cells with dibutyryl cyclic adenosine 3′:5′-monophosphate antagonizes the effect of CD on the infectivity of poliovirus. Cytochalasin also increased the infectivity of other RNA viruses including parainfluenza virus. However, no augmentation of infectivity is found with vaccinia, and infectibility with adenovirus is decreased by CD.