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 differentiation of bone marrow hematopoietic cells, the so called colony-forming cells, in normal and Listeria monocytogenes infected mice (resistant and susceptible strains). We also studied the effects of lead on the serum colony-stimulating activity (CSA), as well as on the survival of the mice after the infection. The doses of lead acetate were 13, 130 and 1300 ppm for 10, 30 and 70 d. At the end of this dosing, mice were infected with Listeria monocytogenes and killed 24, 48 or 72 h after inoculation of the bacteria. A dose-response suppressive effect of lead 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 susceptible mice the suppressive effect of the infection was evident in all 3 time periods. The administration of lead caused no changes in serum hematopoietic growth factors, thus suggesting this metal acts by direct action on the myelopoietic cells. A significant decrease in host resistance, 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.