Cure of fibroblast monolayers from murine cytomegalovirus infection: phenotypic assessment of rat lymphoid cell population developed on fibroblast monolayers.

Rat and mouse fibroblast monolayers were infected with murine cytomegalovirus (MCMV) by 2 hr incubation to allow virus to penetrate the cells. Then lymph node cells (LNC) from rats infected with MCMV and from untreated rats were added together with human recombinant interleukin-2 (hrIL-2). Cytopathic plaques appeared within 2-3 days. In culture of fibroblasts only, 30-40 plaques per well progressed into confluent cytopathy within 6-8 days. In cultures with LNC syngeneic to fibroblasts, plaques appeared; however, the cytotoxic T lymphocyte population that developed and specific apoptotic fragmentation eliminated the cytomegalic cells in the plaques. The surrounding cells stretched to the area, the cytopathic plaques disappeared, and the monolayer resumed its uninfected texture. No plaque-forming units could be isolated from such cured cultures. In allogeneic combination there was no apoptotic target cell killing. However, in cultures stimulated by hrIL-2, plaque growth was arrested and the plaques remained rudimentary. Similarly, arrest of plaques was also obtained in cultures containing LNC from uninfected rats, but only if stimulated by hrIL-2. In mouse fibroblasts carrying the rat LNC, plaque growth was not arrested, and the culture developed into confluent cytopathy. Interferon (IFN)-gamma or -alpha,beta added 24 hr before and 2 hr after infection abolished plaque appearance or arrested growth. IFN-gamma appeared to be the most effective. Fluids harvested from cured cultures also protected from plaque development. Antibodies to IFN-gamma, but not to IFN-alpha,beta, neutralized this capacity in the culture fluids. It is concluded that IFN-gamma produced by the LNC played a major role in the cure of the fibroblast culture from MCMV infection. A mechanism of cell-mediated immunity operating in resolving virus infection is proposed.