Growth characteristics of human herpesvirus-6: comparison of antigen production in two cell lines

In order to optimize viral antigen production, the growth characteristics of human herpesvirus-6 (HHV-6) (strain AJ) were studied in two cell lines: HSB-2 and JJHAN. The cells were infected with different multiplicities of infection (moi) and viral growth was monitored by appearance of cytopathic effect (CPE), total and viable cell count, immunofluorescence test, immunoblotting, and electron microscopy. Although > or = 70% of JJHAN cells showed CPE when infected at high moi, only 5% of the cells contained viral antigens when tested with immunofluorescence. In contrast the percentage of cells showing fluorescence in HSB-2 cells reached > or = 30% when infected at > or = 1:50. More than 10 polypeptides of molecular weight ranging between 31-140 kD appeared in the HSB-2 cultures by immunoblotting while only 3 polypeptides were detected in the JJHAN cultures at high moi. Different stages of virus maturation were seen in the HSB-2 cells by electron microscopy but the replication of the virus in JJHAN cells appeared to be restricted. For the purpose of antigen production the optimal conditions for the AJ strain of HHV-6 were found to be culturing in HSB-2 cells at a concentration of 1:25-1:50 infected to uninfected cells and harvesting after 7 days.