Effect of IFN-γ-induced up-regulation of HLA class I expression on the NK-mediated lysis of autologous MSCs. (A) Analysis of the surface density of HLA class I, Nectin-2, PVR, and ULBP3 molecules on IFN-γ-treated and untreated MSCs derived from donor 15. Filled profiles represent the antigen expression on untreated MSCs, whereas thick lines refer to MSCs exposed to 100 U/mL IFN-γ for 48 hours. Open profiles represent the negative control. (B) Percentage of lysis of untreated or IFN-γ-treated MSCs. Source of autologous effector cells were polyclonal NK cells or the KIR2DL2/3⁺ NKG2A^- F40 clone or the KIR^-- NKG2A⁺ P40 clone. The E/T ratio was 6:1 for polyclonal NK cells and 10:1 for the NK-cell clones. Cytolytic assays were performed in the absence of mAbs () or in the presence of anti-CD94/NKG2A () or anti-HLA class I (▪) mAb. Data are representative of experiments performed by using MSC and autologous polyclonal or clonal NK cells derived from 5 different donors.