Vα24NKT cells are lymphocytes expressing both T-cell antigen receptors and NK-cell antigen receptors on their cell surface and are involved in tumor immunity. They exert their antitumor effects after being activated by a specific ligand, α-galactosyl ceramide (α-GalCer). Malignant pleural effusion, a frequently occurring complication in patients with lung cancer, contains numerous lymphocytes. In the present study, we examined the presence and functions of Vα24NKT cells in the lymphocytes in pleural effusion in vitro. The subjects were 13 untreated patients with primary lung cancer, who suffered malignant pleural effusion as a complication and who were treated between April 2004 and October 2007 at our hospital. Mononuclear cells were separated from the malignant pleural effusion and incubated with α-GalCer and IL-12. The production of IFN-γ and IL-4 after incubation and the proportion of the Vα24NKT cells before and after incubation were determined and compared. In the group cultured with α-GalCer alone, no significant increase in IFN-γ production was observed in comparison with the control group. In the group cultured with α-GalCer + IL-12, IFN-γ production increased significantly in comparison with the control group, and the proportion of Vα24NKT cells increased after incubation. IL-4 production was very much lower than IFN-γ production. Vα24NKT cells were present in malignant pleural effusion in patients with lung cancer, but IFN-γ production did not increase after addition of α-GalCer alone. The Vα24NKT cells were activated by α-GalCer in the presence of IL-12. The Vα24NKT cells in malignant pleural effusion were not activated by α-GalCer alone, suggesting that Vα24NKT cell function is attenuated in malignant pleural effusion.

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