The effect of steroids on the circulating lymphocyte population. II. Studies of the thoracic duct lymphocyte population of the guinea pig after neonatal thymectomy and prednisolone treatment.

The effect of corticosteroids on the lymphatic tissue and circulating lymphocyte pool in the guinea pig has been studied. No signs of increased lymphocytolysis was seen and only after 1--2 weeks treatment with a long acting corticosteroid was the thymic cortex reduced and thymic weight decreased. Three hours after injecting a short acting steroid a 30--40 per cent reduction in the thoracic duct cell count was seen in both control and thymectomized animals. Restitution to pretreatment cell level was completed in 17 hours. Mononuclear cells in the blood were markedly depressed up to 40 hours. The changes in the circulating lymphocyte pool in the resistant guinea pig seem to be in principle the same as in the sensitive rat but less pronounced. It can be concluded that the lymphocyte level in the circulating pool is thymus dependent but restoration of the cell count after steroid treatment is independent of intact thymic function. This data supports the hypothesis of lymphocyte trapping and redistribution after a single steroid treatment.