The influence of prednisolone on the recirculation of peripheral blood lymphocytes in vivo.

In humans and in laboratory animals, administration of a single does of glucocorticosteroids induces a rapid and transient decrease in the numbers of peripheral blood lymphocytes through a redistribution of circulating lymphocytes. This lymphocytopenic effect is an important factor in the immunosuppressive capacity of corticosteroids. We have investigated whether the redistribution is due to an increased influx of circulating lymphocytes from the blood into the lymphoid organs or to a decreased efflux from the organs. Fluoresceinated lymphocytes were injected intravenously in unrestrained normal and prednisolone-treated rabbits and the distribution curves in the peripheral blood were analysed on the basis of a two-compartment model (known from pharmacokinetic studies). In this way, it is shown that the rapid fall in peripheral blood lymphocyte numbers induced by prednisolone is due to a decreased efflux of circulating lymphocytes from the lymphoid organs. In addition, it is demonstrated that prolonged infusion of prednisolone leads to an altered distribution pattern of the circulating lymphocytes among the organs.