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Prepublished online as a Blood First Edition Paper on September 11, 2003; DOI 10.1182/blood-2002-07-2270.
Submitted July 26, 2002
Laboratory of Experimental Hematology, Leiden University Medical Center, Leiden, The Netherlands * Corresponding author; email: W.E.Fibbe{at}LUMC.nl.
Since endotoxins are potent inducers of stem cell mobilization, we hypothesized that their presence in the gut may play a role in cytokine-induced mobilization. To address this possibility we added ciprofloxacin and polymyxin B to the drinking water of Balb/c mice mobilized with either interleukin-8 (IL-8), G-CSF or flt3 ligand (FL). The yield of colony forming units (CFU) was significantly reduced in all mice treated with these antibiotics when compared to controls (IL-8: 192±61 vs. 290±64, p<. 05; G-CSF: 1925±1216 vs. 3371±1214, p<. 05, FL: 562±213 vs. 1068±528, p<. 05). Treatment with ciprofloxacin only eliminated aerobic Gram-negative bacteria from the feces without effect on mobilization. Polymyxin B treatment did not result in decontamination but significantly reduced the number of mobilized progenitor cells (HPC) most likely due to the endotoxin binding capacity of polymyxin B. Over 90% of the gastrointestinal flora consists of anaerobic bacteria. Elimination of the anaerobic flora by metronidazol led to a significantly reduced number of mobilized HPC when compared to controls (IL-8: 55±66 vs. 538±216, p< .05,). Germ-free OF1 mice showed a significantly reduced mobilization compared to their wild type controls (IL-8 controls: 378±182, IL-8 germ free: 157±53, p< .05). Finally, we performed reconstitution experiments adding E. coli derived endotoxins to the drinking water of decontaminated mice. This resulted in partial restoration of the IL-8-induced mobilization (67±28 vs.190±98.1, p<. 01). Our results indicate that endotoxins serve as cofactors in cytokine-induced mobilization. Modification of the endotoxin content by antibiotic treatment may affect the yield of cytokine-induced mobilization.
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