Interferon modulation of Marek's disease virus genome expression in chicken cell lines

Lines of chicken lymphoblastoid cells were established from local lesions induced by simultaneous injection of Marek's disease virus and various stimulants of T-cell activation. Lines developed with regular medium had relatively high mean rates of spontaneous expression of viral internal antigen (6.2%). In contrast, lines developed and maintained with conditioned medium generated by mixed-lymphocyte reaction had a 62-fold reduction in the mean rate of viral internal antigen expression (0.1%). The expression rate could be modulated by the removal or re-addition of conditioned medium to the growth medium. Down regulation involved proteins classified as immediate-early (a 14-kDa polypeptide), early (a 38-kDa phosphoprotein), and late (glycoprotein B homologue) antigens, indicating that the block is very early in virus replication. Once initiated in a given cell, replication apparently proceeded unimpeded. Interferon was determined to be largely responsible for the suppressive activity of the conditioned medium, although involvement of other cytokines could not be ruled out. Also, chicken interferon from other sources, including recombinant interferon, was able to similarly suppress viral antigen expression.