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Department of Medicine, University of Vermont College of Medicine, Burlington, VT 05405
Neutrophil retention in and release from the bone marrow is a critical process that remains incompletely understood. Previous work has implicated the CXCR4/stromal derived factor-1 (SDF-1) chemokine axis in the marrow retention of neutrophils, yet the adhesion pathways responsible for this retention are unknown. Because
4β1 integrin (VLA-4) and its ligand VCAM-1 play a central role in the interactions of hematopoietic stem cells, lymphocytes, and developing neutrophils in the marrow, we investigated whether this integrin might be involved in marrow neutrophil retention and release. In this study, we show that VLA-4 is expressed on murine marrow neutrophils and decreases with maturation, whereas blockade of this integrin leads to the release of marrow neutrophils. Marrow neutrophils adhere via VLA-4 to VCAM-1, which is expressed on marrow endothelium and stroma, and inhibition of VCAM-1 causes release of marrow neutrophils. Furthermore, SDF-1 (CXCL12) signaling through neutrophil CXCR4 augments VLA-4 adhesion to VCAM-1 in vitro, an effect that is blocked by preincubation with pertussis toxin. In vivo blockade of both CXCR4 and
4 causes synergistic release of marrow neutrophils, showing that cross-talk between CXCR4 and VLA-4 modulates marrow retention of these cells. Taken together, these results indicate that the VLA-4/VCAM adhesion pathway is critical in the retention and maturation-controlled release of neutrophils from the marrow, while providing an important link between the CXCR4/SDF-1 signaling axis and the adhesion events that govern this process.
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1 This work was supported by Grants R01 HL084200 and NCRR P20RR15557 from the National Institutes of Health.
2 J.M.P. and C.C.L. contributed equally to this work.
3 Address correspondence and reprint requests to Dr. Benjamin T. Suratt, University of Vermont College of Medicine, 149 Beaumont Avenue, Burlington, VT 05405. E-mail address: benjamin.suratt{at}uvm.edu
4 Abbreviations used in this paper: SDF-1, stromal derived factor-1; DAPI, 4',6'-diamidino-2-phenylindole; LPAM, lymphocyte Peyers patch adhesion molecule.
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