Measurement of Herpes Simplex Virus by the Plaque Technique in Human Amnion Cells

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Abstract
Summary: A plaque technique is described for enumeration of infective units of herpes simplex virus in primary cultures of human amnion cells. Sharply defined plaques which measured 3–4 mm in diameter formed in infected amnion cell monolayers under an agar overlay in 4 days. The number of plaques was directly proportional to virus concentration. In replicate cultures from the same amnion simultaneously inoculated determinations of herpes virus concentration were highly reproducible. In determinations in cultures of variable age obtained from different amnions considerable variation was encountered. This was due largely to two factors: a) Different amnions vary in sensitivity to herpes virus in tissue culture, and b) sensitivity of amnion cells diminishes with age of cultures. Procedures for the control of these variables are discussed.