Effect of IL-3 and E. coli LPS on the proliferation of mouse bone marrow cells in vitro

Bone marrow cells from adult BALB/c mice were cultured at 37 degrees C, with 5% CO2 in air, in RPMI 1640 medium complemented with fetal calf serum. The addition of IL-3 (5% of WEHI-3-conditioned medium) or E. coli lipopolysaccharides (LPS, 50 micrograms/ml) to the cultures stimulated cell proliferation (1.29- and 1.22-fold, respectively, relative to control culture), whereas the simultaneous addition of the two factors reduced the number of cells recovered by 38% relative to those from control cultures (which were around 2.83 x 10(5) cells for each 10(6) plated cells). The frequency of blasts and cells with surface Ig presented the same pattern of variation (0.07 and 0.02%, respectively, in control cultures). The inhibitory effect of IL-3+LPS on cell proliferation was evident from the first day of culture, but more apparent on day 3. Macrophage-colony stimulating factor (M-CSF, L929-conditioned medium) and LPS each given alone stimulated proliferation but reduced it when given together. In contrast, fetal liver cells were not affected by the simultaneous addition of IL-3 and LPS or by M-CSF and LPS. The mechanism of action of the cumulative effect of these two factors is unknown. Since crude cell-conditioned medium was used as the source of IL-3, it is possible that another factor present in this medium interacts with LPS to cause the inhibitory effect on cell proliferation.