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Role of lipopolysaccharide in regulating colony-stimulating factor-dependent macrophage proliferation in vitro
Abstract:
Bacterial lipopolysaccharides (LPS) enhance both production of colony-stimulating factors (CSF) and proliferation of mononuclear phagocytes in vivo. The present study was undertaken to determine whether the effects of LPS on CSF-dependent monopoiesis are due solely to enhanced production of CSF or also to direct effects of LPS on the responding progenitor cell. Addition of LPS to CSF-stimulated macrophage populations had different effects, depending upon the concentration of CSF in the cultures. In the presence of optimal to supraoptimal concentrations of CSF, LPS at doses >/=0.01 mug/ml inhibited macrophage colony formation. This inhibitory activity was not due to cytotoxicity of the LPS and was not mediated through prostaglandin synthesis. In the presence of suboptimal concentrations of CSF, minute concentrations of LPS (10(-7) mug/ml) significantly enhanced macrophage colony formation. Both effects of LPS (inhibition and enhancement) appeared to be properties of lipid A since neither effect was noted with cells from LPS-resistant C3H/HeJ mice, whereas both effects could be neutralized by the addition of the antibiotic polymyxin B, which binds to the lipid A portion of LPS. These results suggest that the effects of LPS on monopoiesis in vivo may not be due solely to its capacity to stimulate production of CSF. Rather, LPS may be involved in stimulating monopoiesis both indirectly through stimulation of CSF production and by its effects on the CSF-responsive progenitor cell.
Insights
Bacterial lipopolysaccharides (LPS) affect monopoiesis (white blood cell production) indirectly by boosting colony-stimulating factors (CSF) and directly on progenitor cells. These dual actions influence white blood cell development.
Area of Science:
- Immunology
- Hematopoiesis
- Cell Biology
Background:
- Bacterial lipopolysaccharides (LPS) are known to stimulate the production of colony-stimulating factors (CSF).
- CSF plays a crucial role in the proliferation and differentiation of mononuclear phagocytes, a type of white blood cell.
- The precise mechanisms by which LPS influences monopoiesis, particularly direct effects on progenitor cells, require further elucidation.
Purpose of the Study:
- To investigate whether the effects of LPS on CSF-dependent monopoiesis are solely due to enhanced CSF production or also involve direct actions on progenitor cells.
- To characterize the concentration-dependent effects of LPS on macrophage colony formation in the presence of varying CSF levels.
- To identify the specific component of LPS responsible for these effects and explore potential mediating pathways.
Main Methods:
- In vitro culture of macrophage populations stimulated with varying concentrations of CSF and LPS.
- Assessment of macrophage colony formation as a measure of monopoiesis.
- Testing LPS-resistant mouse models (C3H/HeJ) to evaluate the role of lipid A.
- Utilizing polymyxin B to neutralize LPS activity by targeting lipid A.
Main Results:
- LPS exhibited biphasic effects on macrophage colony formation depending on CSF concentration.
- At optimal/supraoptimal CSF levels, LPS (>0.01 mug/ml) inhibited colony formation without cytotoxicity or prostaglandin mediation.
- At suboptimal CSF levels, low LPS concentrations (10(-7) mug/ml) significantly enhanced colony formation.
- Both enhancement and inhibition were linked to the lipid A component of LPS and could be blocked by polymyxin B.
Conclusions:
- LPS influences monopoiesis through both indirect stimulation of CSF production and direct effects on CSF-responsive progenitor cells.
- The lipid A moiety of LPS is responsible for these dual actions, modulating progenitor cell responses.
- These findings suggest a more complex regulatory role for LPS in white blood cell development than previously understood.