Tumors induced by Murine herpesvirus 60 or by cell line NB-78 derived from a tumor induced by Murine herpesvirus 78 show presence of the inducing viruses.

Murine herpesviruses 60 and 78 (MHV-60, MHV-78), closely related to Mouse herpesvirus strain 68 (MHV-68), are oncogenic lymphotropic gammaherpesviruses, which may serve as models for study of human oncogenic gammaherpesviruses such as Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV). In this work, we attempted to detect an analog of the MHV-68 ORF73 gene in tumors induced in mice either directly by MHV-60 or indirectly by MHV-78 via inoculation of NB-78 cells derived from a tumor induced by MHV-78. Besides the ORF73 gene, viral antigen and infectious virus were searched for. We succeeded in inducing lymphomas in mice by NB-78 cells and thus confirmed their transformed character. Importantly, we showed that the tumors induced by either MHV-60 or NB-78 cells were positive for the ORF73 gene, viral antigen and infectious virus. These results confirmed the generally accepted hypothesis about the connection between reactivation of latent gammaherpesviruses and malignant tumorigenesis.