Studies of the activity in chicken serum that stimulates the lymphoid development of the embryonic chicken thymus in organ culture.

Abstract

Some properties of the thymus stimulating activity in chicken serum (TSAS) which is essential for the lymphoid development of the embryonic chicken thymus in organ culture, have been studied and a partial purification has been performed. TSAS resisted heating for 30 min at 60° C but not higher temperatures. During dialysis and ultrafiltration of serum a loss of TSAS down to a constant level of about 50 per cent of the original activity was obtained. TSAS was sensitive to treatment at pH 5 or lower but resisted alkaline pH up to at least pH 10. When serum was fractionated with ammonium sulphate little TSAS precipitated at 2.43 M ammonium sulphate or lower. At higher concentrations TSAS was found in the precipitates, but even at 4.05 M significant activity remained in the supernatant. TSAS was recovered from a fraction dominated by the serum albumins after gel filtration on Sephadex G‐200 and G‐100. Further fractionation by ion exchange chromatography on DEAE‐Sephadex separated the TSAS from serum albumin. These results suggest that part of the TSAS is associated with one or more specific factors with a molecular weight of approximately 70,000. The effect of the partly purified TSAS on the growth and morphologic development of the embryonic thymus in organ culture was studied.