Distribution of T-lymphocyte subpopulation in blood and spleen of normal cattle and cattle with enzootic bovine leukosis

Immunocytochemical and flow cytometry techniques were used to examine T-lym phocyte subpopulations in peripheral blood lymphocytes (PBLs) and spleen fr om cases of enzootic bovine leukosis (EBL) in adult cattle, and from normal cattle (adult and young), with a panel of monoclonal antibodies against bo vine leucocyte differentiation molecules. Both in PBLs and spleen, the perc entages of T-lymphocyte subpopulations (CD3(+), CD4(+), CD8(+), and WCl + g amma delta T lymphocytes) of EBL-affected and normal adult cattle were sign ificantly lower than those of normal young cattle. The percentages of these T-lymphocyte subpopulations in the PBLs of adult cattle with EBL were lowe r than those of normal adult cattle, but the converse was true in the splee n. It is suggested that tumour immunity occurred in the spleen. Histologica l examination revealed no follicular hyperplasia in the spleen, and the pro liferation of neoplastic cells began in the red pulp. It is concluded that the spleen is not the organ initially responsible for the transformation of EEL lymphoma and that neoplastic cells migrating from peripheral blood are metastatic. (C) 1999 W.B. Saunders Company Limited.