Supernatant factors from short-term cultures of thymocytes: effect on DNA synthesis

Supernatants from cultures of unstimulated guinea pig thymocytes were investigated on allogenous thymocytes as regards conditioning effect. DNA synthesis was measured by incorporation of 3H-thymidine. Supernatants taken after different incubation times up to 24 h were used. When used without concentration all supernatants showed stimulating activity. After concentration and fractionation, a stimulating factor was found in supernatants taken after a culture time of 24 h. This factor had a molecular weight above or equal to 70,000 daltons as indicated by gel chromatography. In the same supernatants also an inhibiting factor was indicated.