Chemokine receptors are typically expressed on natural killer cells, which can be activated by membrane ligands including the membrane chemokine fractalkine (mFKN). This study investigated the function of mFKN on natural killer (NK) cell activation for interferon (IFN)-γ production and cytotoxicity against tumors. HeLa cells were transfected with a membrane human fractalkine (mhFKN)-expressing vector, and the transcription and surface expression of mhFKN in transfected HeLa cells were confirmed by RT-PCR analysis and immunofluorescence assay, respectively. After co-culture of NK-92 cells with FKN-HeLa cells, the intracellular IFN-γ in the NK-92 cells significantly increased compared to mock-HeLa cells. The concentration of IFN-γ also increased in the supernatant of the NK-92 cells stimulated with FKN-HeLa cells. Moreover, the cytolytic activity of NK-92 cells against K562 target tumor cells was significantly enhanced at each effector:target ratio in 4-h 51Cr-release assays when the NK-92 cells were pretreated with FKN-HeLa, indicating that membrane fractalkine activates the NK cells in the killing process. This study further confirms that membrane-expressed fractalkine plays a critical role in NK cell activation.

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