“…It has been reported that crude extracts from lymphoid tissue contain several unidentified, nonspecific suppressive factors (Hiestand et al, 1977;Blazsek & Gaal, 1978) as well as compounds like thymidine (Kasahara & ShioriNakano, 1976;Lenfant, Garcia-Giralt, Thomas & di Giusto, 1978) and the polyamines (Allen, Smith, Curry & Gaugas, 1977). Since these factors could interfere with the test systems used in our study, TCF was further purified by ion exchange chromatography.…”