ENHANCEMENT OF IN VIVO INCORPORATION OF LABELED PRECURSORS INTO DNA AND TOTAL PROTEIN OF MOUSE LYMPH NODES AFTER ADMINISTRATION OF THYMIC EXTRACTS

Abstract

Particle-free sodium chloride and acid phosphate buffer extracts of thymic tissue obtained from either mice, rats, or calves were injected into male CBA mice. After 24 hr, a significant increase was noted in pulse-label H3-thymidine incorporation into the nucleic acids of peripheral lymph nodes as compared to control groups receiving injections of saline or buffer. After 3 daily injections of extracts (72 hours) further increments in H3-thymidine incorporation into lymph nodes were observed. Increased pulse-label glycine-2-C14 incorporation into total protein and significantly increased lymph node weight also noted at this time. Bovine serum albumin and extracts of rat lymph nodes and spleen did not produce similar effects. It is suggested that the effects of the thymic extracts on lymph node proliferation are due to the presence of a thymic lymphocytopoietic factor. The assay method described should be useful in chemical characterization of this factor and in studies of its mode of action.