Inhibition of mitosis and tritiated DNA precursor uptake in human leucocyte cultures by rat lymph node extract

A water soluble extract was prepared from the lymph nodes of rats of different age groups. This extract, when added to human peripheral blood leucocyte cultures, inhibits DNA synthesis and mitosis when added in different concentrations for varying lengths of time in culture. Also, it was observed that the extract from old rats was not as effective as that from younger animals.