Fig. 4

Enhanced MHC-I expression increases targeting of CICs by CTLs, but diminishes NK cell lysis. a Flow cytometry histograms (representative of five independent experiments) demonstrating enhanced expression of MHC-I after 24 h treatment with IFN-γ; isotype control (filled), untreated cells (open), cells treated with IFN-γ (tinted). CTL and NK cell assays (representative of two independent experiments) showing percent lysis of target cells co-cultured with either primed splenocytes (b) or NK cells (c). TC-1 non-CICs (closed circles), CICs (open circles), non-CICs treated with IFN-γ (closed triangles), or CICs treated with IFN-γ (open triangles). CICs are less susceptible to CTL lysis than non-CICs at all effector to target (E:T) cell ratios (n = 3) 100; P < 0.001, 50; P < 0.001, 30; P = 0.009, 10; P < 0.001. CTL lysis of CICs expressing enhanced MHC-I after IFN-γ treatment did not reach the same level as for non-CICs with and without IFN-γ treatment (E:T ratio 100; P < 0.001, 50; P = 0.029, 10; P < 0.001). CICs are significantly better targeted by NK cells than non-CICs and CICs or non-CICs treated with IFN-γ at all E:T cell ratios (n = 4); P < 0.001. Error bars are standard deviation