Resistance of neonatal human lymphoid cells to infection by herpes simplex virus overcome by aging cells in culture.

Mononuclear leukocytes freshly harvested from human umbilical cord blood were refractory to infection by herpes simplex virus (HSV) type 1, whereas cells aged in vitro for a week produced 10- to 100-fold or greater more virus. Increased sensitivity of aged cells to infection by HSV was not dependent on active DNA synthesis by the cells at the time of exposure to HSV. The aging phenomenon was not due to the outgrowth of a specific cell subpopulation that is uniquely susceptible to HSV because increased sensitivity to HSV type 1 occurred in a variety of cell subpopulations enriched or depleted of T lymphocytes, phagocytic cells, or adherent cells. About 25% of aged cells contained virions detectable by electron microscopy, considerably more cells than formed infectious centers. These virions were seen in large activated lymphocytes which are the principal cell subpopulation present in the aged cultures, but virions were also seen in small lymphocytes.