Plaque size reduction as a measure of viral cell-mediated immunity.

This new assay of viral cell-mediated immunity is sensitive, reproducible, and in many ways resembles the in vivo state. The spread of herpes simplex virus between adjacent monolayer cells was inhibited in the presence of spleen cells from guinea pigs sensitized to that virus. This in vitro control of viral growth was quantified by determining plaque size in monolayers to which were added sensitized spleen cells as opposed to nonsensitized or no spleen cells. The simple measurement of plaque size reduction as an in vitro test of viral cell-mediated immunity is described. In addition to correlating highly with skin testing and macrophage migration inhibition as a test of viral cell-mediated immunity, the ability of sensitized spleen cells to reduce plaque size developed by day 7, paralleling the onset of delayed cutaneous hypersensitivity. The specificity of this lymphocyte-mediated interaction was demonstrated by the inability of herpes simplex virus-sensitized spleen cells to alter the growth of vaccinia virus in cell culture. A ratio of sensitized spleen cells to monolayer cells of 6:1 resulted in significant plaque size reduction on both HEp-2 and conjunctiva monolayers. The data presented demonstrate the potential usefulness of plaque size reduction as a technically simple, specific, and more direct measure of cellular antiviral activity.