Studies on thymus products. I. Modification of rosette-forming cells by thymic extracts. Determination of the target RFC sub-population.

Abstract

Thymic extracts confer on normal bone marrow rosette-forming cells (RFC) in vitro a high sensitivity to anti-theta serum (AθS) and azathioprine (AZ) which they usually lack. Thymic extracts can also confer high sensitivity to AθS and AZ to spleen RFC from adult thymectomized, neonatally thymectomized `thymus-deprived' and nude mice. However, the amount of thymic extracts necessary to get the effect is significantly higher on thymus-deprived and nude mouse spleen RFC than on RFC from spleens of adult thymectomized mice or normal mouse bone marrow. Thymic extracts are also active in vivo and there is a good correlation between the in vitro minimum concentration giving AθS and AZ sensitivity to spleen RFC from adult thymectomized mice and the in vivo minimum dose giving such an effect after intravenous injection. The effect of extract in vivo does not appear before the fourth hour after the injection and is transient, disappearing after 48 hours. Injection of thymic extracts induces the appearance of a `thymic activity' (TA) in the serum with a short half-life (2 hours). Injection of thymic extracts into normal mice does not modify sRFC characteristics in spleen, lymph nodes and bone marrow. It is suggested that thymic extracts act reversibly on a population of T-RFC precursors.