THE EFFECT OF LEAD ON THE BONE-MARROW STEM-CELLS OF MICE INFECTED WITH LISTERIA-MONOCYTOGENES

We investigated the effects of lead exposure on the growth and differe ntiation of bone marrow hematopoietic cells, the so called colony-form ing cells, in normal and Listeria monocytogenes infected mice (resista nt and susceptible strains). We also studied the effects of lead on th e serum colony-stimulating activity (CSA), as well as on the survival of the mice after the infection. The doses of lead acetate were 13, 13 0 and 1300 ppm For 10, 30 and 70 d. At the end of this dosing, mice we re infected with Listeria monocytogenes and killed 24, 48 or 72 h afte r inoculation of the bacteria. A dose-response suppressive effect of l ead was observed in both strains in the 3 periods studied. However, in the resistant strain of mice the suppressive effects were overcome 48 h after the administration of the bacteria, whereas in the susceptibl e mice the suppressive effect of the infection was evident in all 3 ti me periods. The administration of lead caused no changes in serum hema topoietic growth factors, thus suggesting this metal acts by direct ac tion on the myelopoietic cells. A significant decrease in host resista nce, as measured by the mortality rate, was found when both strains of mice were challenged with sub-lethal doses of Listeria monocytogenes. Lethality was determined for a period of 10 d after dosing with 1300 ppm lead for 30 d.