Persistent Varicella-Zoster virus infection in a human rhabdomyosarcoma cell line and recovery of a plaque variant

Varicella-zoster virus (VZV) has been found to persistently infect the human rhabdomyosarcoma cell line A204. Infectious center assays and fluorescent antibody staining demonstrated continuous production of infectious VZV and viral antigen. The level of infection determined by fluorescent antibody staining was variable, and usually only a small percentage of the cells were capable of producing plaques in permissive fibroblasts. The extent of infection was similar in cell cultures passaged at split ratios of 1:2 or 1:10 and grown at 33 or 37 degrees C. VZV recovered from A204 cells several months after establishment of the persistent infection had markedly increased syncytia-forming activity as compared with the parental VZV grown in human diploid fibroblast cells and the three monkey kidney-derived cell lines Vero, CV-1, and MA104. The expression of this altered phenotype continued after serial passage of the cell-associated virus in human diploid fibroblast and Vero cells. Consequently, we designated the reisolated VZV as plaque variant A. The buoyant densities of VZV plaque variant A and VZV DNAs in CsCl gradients were indistinguishable.