FIG. 5.

Influenza virus HA downregulates the ζ chain of NK cells through the lysosomal pathway. (A to D) Primary NK cells were left untreated or were treated with 1 μg/ml HA for 24 h. The cells were collected and then determined for their redirected lysis against P815 cells in the presence of anti-NKp46 (A), anti-CD56 (B), or isotype control antibody (A, B) at the indicated E/T ratios (A) or an E/T ratio of 30:1 (B), and for the intracellular expression of the ζ chain (C) with the mean fluorescence intensity (MFI) being determined (D). (E) After incubation with or without 1 μg/ml HA for 6 or 24 h, the cells were fixed, permeabilized, and examined for ζ chain expression by flow cytometry. (F, G) NK cells were left untreated or were treated with 1 μg/ml HA for 24 h. The cells then were determined for their redirected lysis against P815 cells in the presence of anti-NKp30 or isotype control antibody at the indicated E/T ratios (F) and for the expression of NKp30 on the cell surface (G). (H, I) After being left untreated or being treated with filomycin or E-64 and pepstatin A (EP) for 30 min, NK cells were left unincubated or were incubated with 1 μg/ml H1N1 HA in the presence or absence of these reagents for 24 h. Cells were fixed, permeabilized, and determined for ζ chain expression by flow cytometry, and the MFI was determined. The data shown are means ± SEM from four different donors. *, P < 0.05; **, P < 0.01.