Latency of herpesvirus of turkey and Marek's disease virus genomes in a chicken T-lymphoblastoid cell line.

The properties of latent herpesvirus of turkey (HVT) and Marek's disease virus (MDV) genomes have been studied in virus-non-producer MDCC-BO1(T) cells, a T-lymphoblastoid cell line derived from spleen cells of an HVT-vaccinated chicken. The numbers of the two virus genomes in BO1(T) cells remained stable at 1.6 to 1.8 HVT genome equivalents/cell and 3.4 to 3.8 MDV genome equivalents/cell throughout a number of passages and were not decreased by the presence of phosphonoacetic acid in the culture. When the culture temperature of the MDV-producer MDCC-MSB1 cell line was shifted from 41 to 37 degrees C, the cells cultured at 37 degrees C contained about five times as many virus genomes as those cultured at 41 degrees C. In contrast, the numbers of the two virus genomes in BO1(T) cells were not increased by culture at 37 degrees C. RNA extracted from BO1(T) whole cells and from the polyribosomal fraction hybridized to both MDV and HVT DNAs, indicating the expression of both latent virus genomes. Digestion of cell nuclei with micrococcal nuclease revealed that both latent HVT and MDV genomes possess a nucleosomal structure. Closed circular MDV DNA was demonstrated in BO1(T) by isopycnic centrifugation of DNA in ethidium-bromide-CsCl gradients.