Spontaneous and induced herpesvirus genome expression in Marek's disease tumor cell lines

Abstract

Newly established Marek''s disease tumor cell lines (31) were incubated at 41.degree. C for 48 h after subculturing and then were examined to determine the spontaneous rates of expression of viral internal antigen(s), viral membrane antigen(s) and virus isolation. All but 2 of the lines were isolated from tumors induced by clone-purified Marek''s disease virus strains JM-10, GA-5, RB-1B and BC-1A in 9 different genetic strains of chickens with defined histocompatibility antigens. The line-to-line variations in the rates of spontaneous expression for the antigens or virus rescue were great but the levels of expression were very low in most cases. The median rates of expression for viral internal antigen, viral membrane antigen and virus isolation were 32, 8 and 2 positive cells/105 cells, respectively (ranged, 0-20,280, 0-22,990 and 0-220 positive cells/105 cells, respectively). The ratio of viral internal antigen expression to virus isolation was extremely variable and often high; the ratio of viral internal antigen to viral membrane antigen expression was more consistent and generally low. The virus strain which induce the cell line influenced the level of virus genome expression but the cell genotype did not. Cell lines transformed by JM-10 virus, which exhibited low oncogenicity, had significantly (P < 0.01) higher rates of expression than cell lines transformed by GA-5 and RB-1B viruses, which exhibited high oncogenicity. Treatment with iododeoxyuridine or incubation at 37.degree. C induced increased rates of expression in most lines but not in all lines. The degree of enhanced expression was inversely proportional to the rate of spontaneous expression.