Stimulatory effect on DNA synthesis of thymus and spleen extract from leukemic AKR mice.

A 30,000-50,000 molecular weight (MW) extract of thymus and spleen from 11 age groups of untreated AKR mice, 1-210 days old, was tested for in vitro effect on thymidine incorporation into normal AKR lymph node cells, normal spleen cells, and leukemic thymocytes. Extracts from mice up to 5 months of age mostly had slightly inhibitory effect but concomitant with emergence of thymus leukemia in the 6-month-old mice, the extract acquired a strongly mitogenic effect on normal lymph node cells. Seven-month-old, non-leukemic animals again yielded extracts with inhibitory effect.