Clonal extinction of myelomonocytic leukemic cells by serum from mice injected with endotoxin

Culture of WEHI-3B myelomonocytic leukemic cells in semi-solid agar medium containing post-endotoxin serum led to the development of maturing granulocytes and macrophages in most leukemic colonies. Colony size was consistently increased but the colony content of colony-forming cells (stem-cell self-replication) was markedly reduced. Serial recloning of WEHI-3B colony cells in the continuous presence of post-endotoxin serum led to clonal extinction of the leukemic cells in five of seven experiments. These effects of post-endotoxin serum on WEHI-3B cells were not seen in clonal cultures of 10 other tumor lines. Serum with the capacity to induce differentiation in WEHI-3B cells could be induced by the injection of as little as 0.1 microgram endotoxin and by purified bacterial cell-wall preparations. Serum activity reached peak levels 3 - 6 h after endotoxin injection and returned to preinjection levels within 48 h.