Plaque reduction neutralization test for human cytomegalovirus based upon enhanced uptake of neutral red by virus-infected cells

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Abstract
Foci of cells infected with human cytomegalovirus were noted to stain more intensely than uninfected cells with neutral red, and this provided the basis for development of a plaque assay and plaque reduction neutralization test for cytomegalovirus. Plaques demonstrable by neutral red staining could be counted at 8 days after infection; thus, results could be obtained earlier than for plaque assay systems based upon the viral cytopathic effect, a fewer manipulations were required for staining cell monolayers to demonstrate plaques. Certain variables affecting plaque size and numbers and antibody titers were defined. Addition of fresh guinea pig complement to the reaction mixtures markedly enhanced cytomegalovirus-neutralizing antibody titers of hyperimmune animal sera, but titers of human sera were enhanced only two-or fourfold.