Fractalkine-Mediated Endothelial Cell Injury by NK Cells

Abstract

Endothelial cells (ECs) are primary targets of immunological attack, and their injury can lead to vasculopathy and organ dysfunction in vascular leak syndrome and in rejection of allografts or xenografts. A newly identified CX3C-chemokine, fractalkine, expressed on activated ECs plays an important role in leukocyte adhesion and migration. In this study we examined the functional roles of fractalkine on NK cell activity and NK cell-mediated endothelial cell injury. Freshly separated NK cells expressed the fractalkine receptor (CX3CR1) determined by FACS analysis and efficiently adhered to immobilized full-length fractalkine, but not to the truncated forms of the chemokine domain or mucin domain, suggesting that fractalkine functions as an adhesion molecule on the interaction between NK cells and ECs. Soluble fractalkine enhanced NK cell cytolytic activity against K562 target cells in a dose- and time-dependent manner. This enhancement correlated well with increased granular exocytosis from NK cells, which was completely inhibited by the G protein inhibitor, pertussis toxin. Transfection of fractalkine cDNA into ECV304 cells or HUVECs resulted in increased adhesion of NK cells and susceptibility to NK cell-mediated cytolysis compared with control transfection. Moreover, both enhanced adhesion and susceptibility of fractalkine-transfected cells were markedly suppressed by soluble fractalkine or anti-CX3CR1 Ab. Our results suggest that fractalkine plays an important role not only in the binding of NK cells to endothelial cells, but also in NK cell-mediated endothelium damage, which may result in vascular injury.

Soluble Fractalkine Prevents Monocyte Chemoattractant Protein-1-Induced Monocyte Migration via Inhibition of Stress-Activated Protein Kinase 2/p38 and Matrix Metalloproteinase Activities

“…The membraneanchored form of FKN can be cleaved from the cell membrane by proteolysis to yield s-FKN (18,20,21). The resulting shedded FKN contains the chemokine domain and the mucin-like stalk domain and, conversely to the membrane form of FKN, behaves as a potent chemoattractant for almost all NK cells (65), T lymphocytes (18,22,66), and dendritic cells (24,67). Migration of monocytes in response to s-FKN is still under debate.…”

Expression of fractalkine and its receptor, CX3CR1, in atopic dermatitis: Possible contribution to skin inflammation

“…The membrane-bound FKN is able to mediate firm adhesion of CX 3 CR1-expressing leukocytes without requiring selectin-mediated rolling or activation of integrins 18,19 . Furthermore, FKN is released from the cell surface by proteolytic cleavage as soluble FKN (sFKN) that has potent chemoattractant activity for CX 3 CR1 + leukocytes and activates them 12,17,20 …”

IL-1β and IFN-γ induce the expression of diverse chemokines and IL-15 in human and rat pancreatic islet cells, and in islets from pre-diabetic NOD mice

“…It is a unique chemokine since it is located on a membrane bound mucin stalk and is in transmembrane and soluble shed forms [26]. Fractalkine has adhesive properties, promoting leukocyte migration and enhancing the cytotoxicity of NK cells [27] and cytotoxic T-lymphocytes [28]. Fractalkine has an important role in cardiac allograft rejection [29,30], and it is expressed in mononuclear cells during renal inflammation [31].…”