Glucocorticoid effects on peripheral blood lymphocytes in cows infected with bovine leukemia virus

We examined the effects of glucocorticoids on peripheral blood lymphocytes (PBL) in lymphoproliferative conditions associated with bovine leukemia virus (BLV): persistent lymphocytosis (PL) and lymphosarcoma cell leukemia (BLSL). The effects of hydrocortisone 21-sodium succinate (HSS) on spontaneous incorporation (SI) and mitogen-stimulated incorporation of radiolabeled-thymidine and the effects of intramuscular administration of prednisolone acetate were studied. An expanded population of B lymphocytes in cows with PL was remarkable sensitive to glucocorticoids in vitro and in vivo. SI was markedly inhibited by concentrations of HSS as low as 10(-7) M. These results correlated well with in vivo observations, where an 80%-90% decrease in PBL occurred during the course of glucocorticoid administration. The decrease in total lymphocytes was accounted for almost entirely by a decrease in the expanded B lymphocyte population. Steroid-sensitive lymphocytes together with steroid-resistant cells were observed in cows with BLSL. The reduction in the steroid-sensitive lymphocytes was associated with rapid disease progression in cows with lymphosarcoma. Steroid-sensitive lymphocyte populations in cows with BLSL may include the same reactive B-cell population found in cows with PL. Glucocorticoids may prove to be a useful tool for study of the immune response to the oncogenic virus and lymphoma in BLV-infected cattle.