(A) Representative fluorescence histogram profiles of the expression of the GPI-anchored membrane protein CD48 (solid peaks) by normal peripheral blood T cells, B cells, and NK cells. Negative control antibody staining is shown by the clear histogram peaks. No GPI-deficient cells were detected amongst normal lymphocytes. (B) Representative staining profiles of CD48 expression by T cells, B cells, and NK cells from three patients with PNH. Individual histograms show clear bimodal distributions, with GPI-deficient and GPI⁺ populations readily discernible in all cases. Two particular features are noteworthy: (1) The lymphocytes from case PNH063 show a partial GPI-deficiency. This is similar to their partially deficient (type II) RBCs. (2) In two of the three patients the proportion of GPI-deficent NK cells is much higher than the proportions of B and T cells. (C) For comparison, typical CD59 histogram profiles of lymphocyte subpopulations for case PNH072 are shown. Again, the proportion of NK cells that are GPI-deficient exceeds that of B and T cells.