Regulation of normal hemopoiesis in the acute leukemia L5222

Normal hemopoiesis becomes markedly depressed in rats during the development of the rat leukemia L5222. Whether this could be due to the influence of a circulating humoral factor was investigated by comparing the growth of normal bone marrow cells in diffusion chambers implanted into the peritoneal cavity of normal or leukemic hosts. Similar growth in total cell numbers was observed in both groups of hosts, and no significant difference could be detected between them. In an attempt to exclude the possibility that an inhibitor either did not penetrate to the peritoneum or was inactivated by the chamber membrane, normal serum, or serum from a highly leukemic rat was mixed with the bone marrow cell suspension in the chambers. Again, no difference in growth between the 2 groups could be detected. Therefore, the influence of a circulating humoral factor in the depression of normal bone marrow hemopoiesis in this experimental leukemia seems to be ruled out, and the decrease may be attributable to local events in the bone marrow such as short-range factors or cellular interaction between the leukemic and normal hemopoietic cell populations.