Human fractalkine mediates leukocyte adhesion but not capture under physiological shear conditions; a mechanism for selective monocyte recruitment.
Fractalkine is a unique chemokine possessing a long mucin-like stalk and a transmembrane region that has been proposed to act as an adhesion molecule. We investigated the ability of fractalkine to recruit leukocytes from whole blood, using an immobilized fractalkine fusion protein in the parallel-plate flow-chamber assay. Significant adhesion of leukocytes to fractalkine peaked at 2 dynes/cm(2) but was minimal at 10 dynes/cm(2). In contrast, VCAM-1 could recruit cells from whole blood at 10 dynes/cm(2). Co-immobilization of fractalkine and VCAM-1 at 10 dynes/cm(2) resulted in a twofold increase in adherent cells compared with VCAM-1 alone, suggesting that fractalkine can mediate adhesion at high shear if combined with a molecule that can mediate leukocyte tethering. Pretreatment of blood with pertussis toxin eliminated this increase in adhesion, implicating intracellular signaling in fractalkine-mediated mechanisms of adhesion to co-immobilized fractalkine/VCAM-1. Analysis of the cell types recruited to fractalkine alone at low shear, or to fractalkine and VCAM-1 at 10 dynes/cm(2), revealed that monocytes were recruited to fractalkine with the highest specificity. In conclusion, fractalkine is unlikely to act alone at shear forces found in most vascular beds where it most likely co-operates with tethering molecules, e.g. VCAM-1, in the recruitment of monocytes.
Kerfoot
Steven M
SM
Immunology Research Group, Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada.
Lord
Sarah E
SE
Bell
Robert B
RB
Gill
Varinder
V
Robbins
Stephen M
SM
Kubes
Paul
P
D000469:Alkaline Phosphatase / Q000502:physiology; D000073883:CX3C Chemokine Receptor 1; D002448:Cell Adhesion; D002465:Cell Movement; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C / Q000502:physiology*; D006801:Humans; D007962:Leukocytes / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D009000:Monocytes / Q000502:physiology*; D018121:Receptors, Cytokine / Q000032:analysis; D015728:Receptors, HIV / Q000032:analysis; D019010:Vascular Cell Adhesion Molecule-1 / Q000502:physiology
D000073883:CX3C Chemokine Receptor 1; C515538:CX3CL1 protein, human; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D008565:Membrane Proteins; D018121:Receptors, Cytokine; D015728:Receptors, HIV; D019010:Vascular Cell Adhesion Molecule-1; D000469:Alkaline Phosphatase