Screening for specific calf thymus inhibitors (chalones) of T-lymphocyte proliferation

Using agar colony assays with truly proliferating stimulated human T-lymphocytes and mouse granulocytes, two ultrafiltrate fractions were obtained from calf thymus which preferentially inhibited lymphocyte colony growth: Fraction I in the molecular range 1000-10,000 proved to be stable upon heating, prolonged storage and lyophilization, whereas Fraction II in the molecular range 10,000-30,000, was found to be unstable. Fraction I was also extracted with Tween 80 and cetyltrimethylammonium bromide. Chromatography of Fraction I on Biogel P6 and DEAE-cellulose further increased its specificity of inhibition for lymphocyte colony growth and revealed an estimated molecular weight of below 1400. Its inhibitory activity was found to be reversible and unlikely to result from spermine. Thus the properties of fraction I meet the requirements of a T-lymphocyte chalone as an endogenous non-cytotoxic and reversible inhibitor of T-lymphocyte proliferation.