Marek's disease in turkeys: the induction of lesions and the establishment of lymphoid cell lines.

The inoculation of turkeys with large doses of a virulent strain of Marek's disease virus (GA strain), but not of two other virulent strains (HPRS-16 and JM), was found to induce a disease resembling Marek's disease of the chicken. The most prominent lesions were lymphocytic leukaemia and lymphoid and reticular hyperplasia in the spleen and the liver. These developed after a prolonged latent period and the early histological changes (lymphoid cell destruction and reticuloendothelial cell hyperplasia) reported in chickens were not observed.

The role of histocompatibility antigens in cell-mediated cytotoxicity against Marek's disease tumour-derived lymphoblastoid cell lines.

The cytotoxic activity of spleen cells from Marek's disease (MD) virus-infected chickens against syngeneic and allogeneic tumour cell lines was compared, using MD lymphoma-derived lymphoblastoid cell lines obtained from two inbred and two outbred chicken strains. Activity was significantly greater against allogeneic than against syngeneic target cells, although some activity against syngeneic cells was detected. Cold target cell inhibition tests confirmed that unlabelled normal spleen cells could block the cytolysis of tumour cell targets bearing the same histocompatibility antigens as the spleen cells.

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.

The occurrence of chicken foetal antigen after infection with Marek's disease virus in three strains of chicken.

An indirect immunofluorescence procedure employing specific antiserum was used to demonstrate chicken foetal antigen (CFA), a membrane antigen typically present on embryonic cells. The expression of CFA by lymphocytes from the peripheral blood, spleen, thymus and bursa was found to decline rapidly after hatching; the bursa, however, contained about 30% CFA-positive cells until at least 120 days of age. After infection of a genetically susceptible strain of chickens (HPRS Rhode Island Red) with Marek's disease virus, the expression of CFA by lymphocytes in the blood and lymphoid organs was found to increase steadily.

The mechanism of genetic resistance to Marek's disease in chickens.

Genetic resistance to Marek's disease in RPL line-6 chickens is expressed not only at the level of host immunological responses against virus an tumour antigens, but also at the level of target lymphoid cells for virus infection and transformation. The nature of the target cell involved was investigated. Spleen cells from susceptible line-7 chickens adsorbed more Marek's disease virus and turkey herpesvirus in vitro than line-6 spleen cells.

The effect of bursectomy on the adoptive transfer of resistance to Marek's disease.

Immunization with inactivated viral antigens protected chickens against Marek's disease. Non-immunized chickens could be protected by injections of spleen cells but not of serum from immunized, histocompatible donors. Chickens rendered agamma-globulinaemic by bursectomy and irradiation could also be immunized against Marek's disease by inoculation with viral antigens, but spleen cells from these immunized, bursectomized and irradiated donors did not confer protection on the recipients into which they were injected.

The effect of bursectomy on vaccination against Marek's disease with the herpesvirus of turkeys.

Protection against Marek's disease following vaccination with the herpesvirus of turkeys was significantly impaired but not abolished by ablation of the bursa-dependent lymphoid system by surgery and X-irradiation. It was concluded that the humoral immune system is relatively more important in vaccinal immunity induced by the herpesvirus of turkeys compared with that induced by attenuated Marek's disease virus.