Further studies on the mechanism of centrifugal enhancement of cytomegalovirus infectivity.

The phenomenon of centrifugal enhancement of infectivity, previously shown to be an intrinsic property of murine and human cytomegalovirus (CMV) was studied further in an attempt to understand the underlying mechanism of action and to try to influence the phenomenon by means of extrinsic factors. The sand-rat herpes virus also displayed centrifugal enhancement in rat, mouse, and human cells. Further investigations were performed with murine CMV. The property of enhancement was not restricted to a specific phase of cell cycle. A variety of factors, known to influence cellular physiology, did not significantly affect the ratio of centrifugal infectivity to standard infectivity i.e., the c/s ratio. However, it was necessary to centrifuge the infected cultures within one hour of the establishment of infection, since centrifugation after this delay failed to yield the enhancement; but there was no partial effect; the cultures either showed complete centrifugal enhancement or no such effect. Thus, it appears that some herpes viruses, during their initial encounter with susceptible cells, can be forced into preferential productive infection by the process of centrifugation, but after a lapse of an hour or more, centrifugation can no longer do this and most of the infected cells fail to replicate virus. Consequently we continue to recommend low speed centrifugation (1000 x g, for 30 min) in order to enhance CMV detection and to optimize infectivity assays.