Malignant lymphomas of thymus origin in two sows.

Two cases of swine thymic lymphoma were investigated by electron microscopy and the immunoperoxidase method for terminal deoxynucleotidyl transferase (TdT), and furthermore sheep erythrocyte rosette assay was applied to one case. In case 1, immunoblastoid cells predominated and smaller cells were admixed with them. Many neoplastic cells were TdT-positive and formed rosettes with sheep erythrocytes at 4 degrees C, but about half of them formed rosettes at 37 degrees C. Ultrastructurally the neoplastic cells were characterized by highly irregular nuclei, poorly developed organelles and clustered dense bodies. The neoplasm in case 2 was composed of medium-sized to large cells and the latter predominated. A few of the neoplastic cells stained positively with anti-TdT serum. Ultrastructurally the neoplastic cells were characterized by nuclear convolution, narrow cytoplasmic bands and clustered dense bodies. The morphological features of thymic lymphomas were discussed in comparison with those of other swine lymphomas and lymphomas of other animals. Histological and immunological progression into T-immunoblastoid cells in case 1 was also discussed.