Histological aspects of lymphoid organs in chickens with Marek's disease

Twenty chickens with Marek's disease were studied concerning the histological changes in different organs, especially in lymphoid ones (thymus, bursa of Fabricius, spleen). Neoplastic lesions under the form of a poorly differentiated lymphoma were found in peripheral nerves, gonads, liver, spleen, heart, kidneys, thymus and bursa of Fabricius. In birds without neoplastic transformation of the thymus and bursa, these organs were constantly atrophied following dystrophic phenomena affecting the lymphoid cells, a morphologic expression of the productive type of viral infection. The thymus and also the bursa of Fabricius were neoplastic in three chickens. Marek's disease appears as a very suitable model for the microscopic study of the escalation of the immune response into malignant lymphoma.