a, Representative image of immunofluorescence multicolor staining of NK cells (CD56 PE/ CD49a A647/ CD3 FITC) in the upper dermis of cutaneous Ni-ECT lesions. Magnified image to the right. The dotted line in the merged picture indicates the dermal-epidermal junction and the rectangle displays the region of the magnified image. b, Quantitative in situ immunofluorescence analysis of NK cells (CD56+CD3-), NKT cells (CD56+CD3+) and T cells (CD56-CD3+) in the dermis of cutaneous Ni-ECT lesion. Data are given as absolute numbers of positive cells per mm2 ± SD. n = 20. **P < 0.001, ***P< 0.0001. c, Percentage of CD49a+ NK cells in non-lesional and lesional (Ni-ECT) skin to total NK cells. Data are presented as percentage of CD49a+ cells to total CD56+CD3- NK cells ± SD. n = 20. ***P < 0.0001. d, Graphical abstract of the experimental design with antigen-specific killing of nickel-incubated autologous B cells by NK cells of nickel sensitized individuals. e, Antigen-specific lysis of autologous B cells pulsed with “Matched” (nickel) or “Mismatched” (cobalt) antigens by isolated NK cells and T cells from Ni-ECT lesions and blood. Bars represent mean specific lysis ± SD of triplicates. n = 4. *P < 0.05, ***P < 0.0001. f, Nickel-specific cytotoxicity of hepatic NK cells of sensitized individuals. Antigen-specific lysis of autologous B cells pulsed with “Matched” (nickel) or “Mismatched” (cobalt) antigens by isolated NK cells and T cells from blood and liver of patients sensitized to nickel. Results represent mean specific lysis ± SD of triplicates. n=3. **P < 0.001.