Induction of apoptosis in cord blood lymphocytes by HHV-6

Apoptosis induced by human herpesvirus 6 (HHV-6) in cord blood lymphocytes was investigated. Cord blood mononuclear cells (CBMC) prestimulated with phytohemagglutinin (PHA) were infected with HHV-6 and cultured with interleukin 2 (IL-2) for 5 days. Apoptosis was investigated by cell cycle analysis, terminal deoxytransferase (TdT)-mediated dUTP nick end-labeling (TUNEL) assay, and staining with monoclonal antibody APO2.7 reacting with 7A6 antigen. The percentage of the hypodiploid fraction by cell cycle analysis and the percentage of apoptosis determined by TUNEL assay were significantly higher in HHV-6-infected CBMC compared with uninfected CBMC. 7A6 antigen, induced on the mitochondria membrane in apoptotic cells, were mainly expressed in CD4+ cells. 7A6 antigen was also detected in HHV-6-infected cells determined by monoclonal antibody OHV-3 reacting with HHV-6 glycoprotein. These data indicated that HHV-6 induced apoptosis in HHV-6-infected cells after stimulation with IL-2 for 5 days. The addition of anti-Fas antibody, anti-Fas ligand antibody, and anti-TNF-alpha antibody did not affect the induction of apoptosis by HHV-6, indicating that the Fas-Fas ligand pathway and TNF pathway did not contribute to the apoptosis induced by HHV-6.