Isolation of Nanjing local strains of HHV-7 and their biological and immunological characteristics

To investigate the biological and immunological characteristics of the Nanjing local strains of HHV-7, four strains of herpesvirus were isolated from saliva specimens of one healthy individual and three children suffering from a kidney disease in Nanjing. The viruses were identified by transmission electron microscopy (EM), indirect immunofluorescence assay (IFA) with a specific monoclonal antibody; nested polymerase chain reaction, restriction mapping and DNA sequencing. The virus-infected cells showed the typical cytophathic effect (CPE) under microscopy and could be detected by IFA with the human herpesvirus-7 (HHV-7) specific antibody. Under EM, herpesvirus-like and virions capsids could be found in their cytoplasm or nucleoplasm. HHV-7 DNA fragments amplified from infected cells by nested PCR were confirmed by restriction mapping and DNA sequencing. Similarly to DC strain, an known HHV-7 strain used in the present study as the positive control, the virus could be inactivated by ultraviolet irradiation for 10 min, heated at 45 centigrade degree for 30 min, pH<5 or>9 at 4 centigrade degree for 2 h and ether or chloroform for 10 h. The virus induced the production of TNF-alpha, IL-10 and IL-12 p 70 while inhibited IFN-alpha secretion, increased the percentage of CD2(+) cells while decreased that of CD4(+) or CD 45 RA(+) cells. The results indicate that the viruses isolated in Nanjing are HHV-7, which has similar biological characteristic to the known HHV-7 strain, DC. Infection with HHV-7 in vitro could affect immune function of lymphocytes by disturbing cytokine production and CD antigen expression.