Enhancement of baculovirus plaque assay in insect cell monolayers by DEAE-dextran.

The presence of DEAE-dextran in the agarose overlay, when titrating wild-type or recombinant baculoviruses by plaque assay, resulted in a higher definition and contrast of viral plaques and increased the plaque number and mean diameter at least by a factor of 2x on day 5 post infection. This increase was related to neither a larger production of infectious virus nor of recombinant protein and did not occur when the polycation was only present in the virus inoculum or when insect cell monolayers were preincubated for 60 min with it. The extension of the observations to a number of different recombinant viruses from varied sources, including several baculoviruses that could not consistently produce plaques in the absence of the polycation, substantiates the use of DEAE-dextran to perform a more reliable, faster and reproducible plaque assay of recombinant baculoviruses.