Apoptosis induced by human cytomegalovirus infection can be enhanced by cytokines to limit the spread of virus

Fas-mediated apoptosis is one of the immune effector pathways leading to th e elimination of virus infected cells. In vivo, apoptotic signals are deliv ered to virus infected cells by Fas-L and other cytokines secreted by speci fic T lymphocytes. Cellular immune response appears to be essential in prev ention of human cytomegalovirus (HCMV) disease. We have hypothesized that H CMV infection might directly or indirectly result in upregulation of Fas re ceptor and in the presence of Fas ligand, lead to apoptosis of infected cel ls. We show that infection of human fibroblasts with HCMV is associated wit h up-modulation of Fas-R process that could be further potentiated by inter feron (IFN-gamma). Using DNA agarose gel electrophoresis, terminal dideoxy transferase reaction, and annexin assay, we demonstrated that in a producti ve HCMV infection of human fibroblasts, loss of cell viability was not only due to virus-mediated cell lysis but also to due to apoptosis, IFN-gamma i nduced relative HCMV resistance and prevented loss in cell viability. In co ntrast, anti-Fas monoclonal antibody CH11, serving as Fas agonist, resulted in an accelerated loss in viability of infected cells, IFN-gamma in combin ation with CH11 further increased the rate of apoptosis and compared to cul tures with CH11 only, this effect was not restricted to only infected cells . While IFN-gamma did not affect the number of cells expressing immediate e arly antigen, it markedly reduced structural protein expression. IFN-gamma in combination with CH11, decreased the expression of HCMV matrix protein p p65, reduced the amount of HCMV DNA and infectious virus produced, Our resu lts are consistent with the theory that cells infected with HCMV can be eli minated by immune effector cells via Fas-mediated apoptosis, IFN-gamma, in addition to its intrinsic antiviral activity, primes HCMV infected cells to the action of Fas ligand and Fas-mediated apoptosis. (C) 1999 Internationa l Society for Experimental Hematology. Published by Elsevier Science Inc.