Detection of biologically active adenovirions unable to plaque in human cells.

Butel, Janet S. (Baylor University College of Medicine, Houston, Tex.), Joseph L. Melnick, and Fred Rapp. Detection of biologically active adenovirions unable to plaque in human cells. J. Bacteriol. 92:433-438. 1966.-Plaque formation in green monkey kidney (GMK) cells by a defective simian virus 40-adenovirus 7 "hybrid" population (PARA-adenovirus 7) was enhanced by the addition of excess adenovirions. Adenovirus types 2, 7, and 12 were capable of providing enhancement, although none of these viruses gives rise to plaques in simian cells in the absence of PARA (particle aiding replication of adenovirus). Near maximal enhancement of the PARA plaque titer on simian cells was obtained with input multiplicities ranging from 0.02 to 0.14 plaque-forming units (PFU) of helper adenovirus per GMK cell. The PFU of helper adenoviruses tested (types 2, 7, and 12) were measured in the most sensitive assay system, human kidney cells. This input corresponded to three to nine helper virus particles per GMK cell. The majority of particles capable of enhancing plaque formation by PARA banded at a density of 1.34 in CsCl. Adenoviruses inactivated by heat or ultraviolet light were not capable of enhancing plaque formation by PARA. Highest titers were obtained when PARA and helper adenovirus were inoculated simultaneously. Inoculation of the helper adenovirus 24 hr prior to the inoculation of PARA resulted in the formation of only 50% as many plaques, and no enhanced plaques developed when the adenovirus preceded PARA by 48 hr. Conversely, the addition of adenovirus 48 hr after the inoculation of PARA initiated 56% as many plaques as simultaneous inoculation; 4% of the enhanced plaques still formed when helper virus was added as late as 5 days after inoculation of PARA. These results suggest that adenovirus particles unable to plaque on human or monkey kidney cells are nevertheless capable of interacting with PARA in simian cells, thereby facilitating replication of both particles.