Discussion Summary: Potential Hazards Related to Other Nonoccupational Exposures*

-Ultrafiltrates from spleen inhibited both DNA synthesis and the proliferation of normal lymphocytes stimulated in culture from both mouse and man without apparent cytotoxicity. However, the same doses of this spleen ultrafiltrate will kill up to two-thirds of the leukaemic lymphoblasts from both mouse and man after 24 h incubation. This unique lymphocytotoxic effect could also be demonstrated on fresh primary cultures of leukaemic lymphocytes and was highly effective on slowly growing established cell lines under crowd culture conditions. Furthermore, ultrafiltrated thymus extract did not affect the DNA synthesis rates or the viability of NC-37 lymphoblasts, which have B cell characteristic. Thymus extract was cytotoxic to Molt cells, which have T cell characteristics.