Propagation and characterization of human herpesvirus-7 (HHV-7) isolates in a continuous T-lymphoblastoid cell line (SupT 1)

Abstract

After initial culture of HHV-7 in PHA-stimulated human cord blood mononuclear cells (HCBMC), six HHV-7 isolates were propagated successfully in an immature continuous T-lymphoblastoid cell line SupT 1. All six isolates infected efficiently the SupT 1 cells, and the infected cells became grossly enlarged and multinucleated 7–21 days post-infection. Various stages of HHV-7 morphogenesis were detected. Cell-free supernatants from HHV-7-infected SupT 1 cells were infectious to HCBMC as well as to SupT 1 cells. The HHV-7-infected SupT 1 and HCBMC cell lysates contained more infectious virus than the centrifuged cell culture fluid supernates from the same culture. The HHV-7 isolates H7-2, H7-3, JHC, and JB, concentrated 500 times, had average infectivity titers of 10 3.0 TCID 50/ml while strains H7-4 and KHR titered approximately 1–2 logs higher. When all six HHV-7 isolates were propagated in SupT 1 and culture fluid supernatants were examined 14–21 days post-infection by negative stain electron microscopy they contained an average of 1.9×10 9 virus particles/liter. IFA and ELISA, using HHV-7/SupT 1 cell lysate as an antigen, seem to correlate well in detecting high and low HHV-7 antibody in sera from chronic fatigue patients and healthy donors as controls. HHV-7 from SupT 1 cell culture was free of HHV-6 and other human herpesviruses as tested by PCR, and the HHV-7 PCR signal was still strong when the viral preparation was diluted to 4.82×10 2 genome copies. Since HCBMC are expensive to obtain and available in only small amounts, it is difficult to obtain large quantities of HHV-7 antigen. On the other hand, the SupT 1 cell is an excellent source to produce consistently sufficient quantities of HHV-7 for purification studies, development of immunodiagnostics, in vivo infectivity studies, evaluation of antiviral drugs, and molecular biological studies.