Upregulation of vitamin D binding protein (Gc-globulin) binding sites during neutrophil activation from a latent reservoir in azurophil granules

Mol Immunol. 2007 Mar;44(9):2370-7. doi: 10.1016/j.molimm.2006.10.011. Epub 2006 Nov 20.


Vitamin D binding protein (DBP) is a multifunctional plasma transport protein that is also found on the surface of many cell types. Cell surface DBP significantly enhances chemotactic activity of complement (C) peptides C5a and C5a des Arg. However, both DBP binding and C5a chemotaxis enhancement can vary among neutrophil donors. To test if activation during cell purification is responsible for this variability, neutrophils were isolated using both standard and lipopolysaccharide (LPS)-free protocols. Cells isolated by the LPS-free method had no DBP-enhanced chemotaxis to C5a or DBP binding to plasma membranes. Moreover, neutrophils treated with LPS bound more avidity to immobilized DBP than sham-treated cells. Subcellular fractionation of neutrophils (standard protocol) revealed a heavy plasma membrane (HM) band that contained components of light plasma membranes and all three granules. The HM band possessed most of the DBP binding activity (58%), and activation of cells with ionomycin greatly increased DBP binding to HM. Azurophil granules contained 33% of the total DBP binding sites and there was a highly significant positive correlation (r=0.988) between release of the granule marker myeloperoxidase and DBP binding. These results indicate that fusion of granules with the plasma membrane forms HM that contains DBP binding sites.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Binding Sites / drug effects
  • Cell Fractionation
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Chemotaxis, Leukocyte / drug effects
  • Chemotaxis, Leukocyte / immunology
  • Complement C5a / immunology
  • Complement C5a / isolation & purification
  • Complement C5a / pharmacology
  • Cytoplasmic Granules / drug effects
  • Cytoplasmic Granules / immunology
  • Cytoplasmic Granules / metabolism*
  • Humans
  • Iodine Radioisotopes
  • Neutrophil Activation / drug effects
  • Neutrophil Activation / immunology*
  • Neutrophils / drug effects
  • Neutrophils / enzymology
  • Peroxidase / metabolism
  • Protein Binding / drug effects
  • Subcellular Fractions / drug effects
  • Up-Regulation* / drug effects
  • Vitamin D-Binding Protein / isolation & purification
  • Vitamin D-Binding Protein / metabolism*
  • Vitamin D-Binding Protein / pharmacology


  • Iodine Radioisotopes
  • Vitamin D-Binding Protein
  • Complement C5a
  • Peroxidase