Influence of corticosteroids on lymphocyte recirculation.

The effect of corticosteroids on cell kinetics and cell size distribution in the circulating lymphocyte population of the steroid sensitive rat and the steroid resistant guinea pig were studied. A single high steroid dose (prednisolone) induced a rapid depression of the lymphocyte level both in normal and thymectomized animals of both species and a restitution within one day. The returning cell population showed the the same size distribution and label index profile as before involution. The main effect of a single steroid dose seems to be a "trapping" of lymphocytes with redistribution from the circulation to some tissues. The difference between the two species seems to be quantitative with a more pronounced trapping mechanism in the sensitive rat but a certain degree of lymphocytolysis cannot be excluded in this species. The steroid action seems to be on both T- and B-lymphocytes and the restitution of cell levels after acute involution is independent of an intact thymic function. The same course of events was observed in the normal rat after stress, but not in the thymectomized rat.