An anatomo-pathological study of the lymphoid system in hamsters during the growth of an SV40-induced tumour.

A systematic histological study of the lymphoid organs of the Syrian hamster was undertaken during development of a tumour induced with SV40 transformed cells. The essential features were: (1) A peritumoral plasma-cell reaction was present until the tumour reached a weight of 4-6 g; then it disappeared. (2) In the thymus an initial increase in mass with progressive infiltration of cortical cells into the medullary region was noted. Coincidentally with the disappearance of peritumoral plasma cells, thymus size descreased. As tumour growth proceeded, the medulla was progressively invaded by cortical and blood-borne cells which eventually made up more than 95% of the total population. (3) The spleen showed sequential changes. An early period of mild banal inflammation characterized by scattered immunoblasts in the reticulum was followed by a reduction in the number of lymphoid follicles, a loss of T lymphocytes in the periarteriolar areas and the appearance in the reticulum of young lymphocytic cells. This change coincided in time with disappearance of the peritumoral plasma cells. This change in turn gave way to a final stage characterized by progressive accumulation in the reticulum of young lymphoblastic cells which gave the spleen a pseudoleukaemic appearance and suggested a hyperimmune state. (4) The lymph nodes were the site of a mild plasmacytic stimulation in the region of the cortico-medullary junction; this persisted throughout tumour growth.