Analysis of HLA-DR and CD45RA expression on normal (CD48⁺) and PNH (CD48⁻) components of peripheral blood T cells by three-color flow cytometry. Initial gating of T cells was based on low SSC characteristics and CD3 positivity as described in Materials and Methods and in Fig 1. The upper two-color dot plots (A through C) show the difference in HLA-DR expression between CD48⁺ and CD48⁻ T cells in 3 representative patients with PNH. The percentage of normal and PNH T cells expressing HLA-DR are shown in the upper and lower quadrants, respectively. Not only is HLA-DR expression absent on GPI negative T cells (plots A and B), but also on T cells with partial GPI deficiency (plot C). The lower dot plots (D through F) show the differences in CD45RA expression by normal (CD48⁺) and PNH (CD48⁻) T cells. The proportion of naive T cells is much higher within the GPI-deficient compartment, independent of whether there is complete (plots D and E) or partial deficiency (plot F) of GPI-anchored proteins. The normal T-cell components have a predominantly memory (CD45RA⁻) phenotype.