STAGES OF MAREKS-DISEASE VIRUS LATENCY DEFINED BY VARIABLE SENSITIVITY TO INTERFERON MODULATION OF VIRAL-ANTIGEN EXPRESSION

Cytokines in conditioned medium can suppress expression of viral inter nal antigens (VIA) in lymphocytes latently infected with Marek's disea se virus. In the present study, conditioned media produced by spleen c ells stimulated with concanavalin A or by mixed-lymphocyte reaction ha d significantly greater (P < 0.05) VIA-suppressive activity with lymph ocytes harvested from birds at 14 days post infection than with those collected at 7 days. This finding defines two stages during the latent period in which sensitivity of lymphocytes to cytokine modulation of viral expression differs. Suppression involved proteins representing i mmediate-early, early and late viral antigens. Physico-chemical charac terization of the suppressive factor in conditioned medium was consist ent with that expected of interferon. Indeed, natural interferon prepa red from avian reovirus-exposed chicken embryo cells, and recombinant chicken interferon, both mimicked the activity of conditioned medium a nd were more suppressive with lymphocytes from the later stage of late ncy.