Abstract
Ultracentrifugation of very dilute suspensions of herpes simplex virus directly onto monolayer cells grown in centrifuge tubes was studied. Enhanced infectivity by ultracentrifugation was similar at 4 degrees C and at 35 to 37 degrees C. The high infectivity levels of cultures centrifuged at 4 degrees C were further examined by infectious center assays. At 4 degrees C, the numbers of infectious centers in control (noncentrifuged) cultures were almost 100-fold fewer than in control cultures at 37 degrees C. However, the numbers of infectious centers in cultures ultracentrifuged at 4 degrees C were similar to those ultracentrifuged at 37 degrees C. The great difference in the numbers of infectious centers between 4 and 37 degrees C control cultures, in contrast to the similarity between 4 and 37 degrees C ultracentrifuged cultures, indicated that ultracentrifugation at 4 degrees C enhanced infectivity possibly by facilitation of herpes simplex virus penetration into monolayer cells.