HLA-E reactivity of IgG purified from the sera of normal nonalloimmunized males negative for anti–HLA-E Abs. These sera were obtained from normal volunteers from Saudi Arabia. The sera are identified with AB numbers. The purified IgG showed HLA-E reactivity (A) and reactivity for a variety of HLA-Ia alleles (B). MFI color code appears below data (B). This same color code can be used to assess MFI values in Figures 4 and 7.