Studies on the role of macrophages in Marek's disease of the chicken.

Macrophage activity in relation to Marek's disease was investigated by determining phagocytic indices in vivo and by examining virus plaque-inhibiting activity of peritoneal macrophages in vitro. No correlation was observed between phagocytic index and resistance in different genetic strains of chickens. Infection with Marek's disease virus increased both phagocytic indices and the plaque-inhibiting activity of peritoneal macrophages, more so in susceptible than in resistant chickens. There was an association between increased macrophage activity and virus replication, and it is suggested that the enhancement of macrophage activity results from activation indirectly caused by the presence of Marek's disease virus or viral antigens.