Nonbursal lymphomas induced by nondefective reticuloendotheliosis virus

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Abstract
In previous studies we described bursal lymphomas similar to those of lymphoid leukosis in line 15x7 chickens inoculated with nondefective reticuloendotheliosis (RE) virus. A different type of neoplastic disease syndrome induced by nondefective RE virus is described in the present study. The tumours were characterised as lymphomas and most commonly involved the thymus, heart, liver, and spleen; the bursa invariably appeared normal or atrophied. Mortality from nonbursal lymphomas occurred as early as 6 weeks post‐inoculation and was as high as 66%. The frequency of nonbursal lymphomas was markedly influenced both by the strain of RE virus and the line of chicken. Maximum tumour induction occurred in line 63 or line 0 chickens inoculated with RE viral strains SN or DIA. Histologically, the tumours were composed of a homogenous population of immature lymphoreticular cells. The tumours were often accompanied by enlarged peripheral nerves which were infiltrated with large, irregular cells with abundant cytoplasm. In an indirect membrane immunofluores‐cent test, the tumour cells reacted weakly with anti‐T cell serum but not with anti‐B cell serum; the cells were refractory to treatment with . either serum in a complement‐dependent antibody cytotoxicity assay. A proportion of the tumour cells contained membrane RE viral antigens. Although this syndrome superficially resembled Marek's disease (MD), nonbursal RE lymphomas lacked the MD tumour‐associated surface antigen and the pleomorphic lymphocyte populations characteristic of MD. The nonbursal lymphomas appeared different from the previously‐described RE virus‐induced bursal lymphomas on the basis of latent period, cell surface antigens, and line susceptibility, and are probably induced by a different molecular mechanism.