Expression of decay‐accelerating factor and CD59 in lymphocyte subsets of healthy individuals and paroxysmal nocturnal hemoglobinuria patients

The expression of phosphatidylinositol (PI)‐anchored complement‐regulatory membrane proteins on circulating blood cells has been well clarified; however, the PI proteins on lymphocyte subsets have not been fully analyzed yet. We examined the expression of decay‐accelerating factor (DAF) and CD59 on the T lymphocytes (CD2−, CD3+, CD4−, and CD8−) and CD20+ B lymphocytes in ten healthy volunteers and 12 paroxysmal nocturnal hemoglobinuria (PNH) patients by cytofluorometry. In healthy controls, each subset of lymphocytes showed a small population of cells weakly positive and a large population of cells strongly positive for DAF and CD59, while erythrocytes showed a single population of cells positive for the PI proteins. The two‐population expression of DAF was most distinctive in CD8− T cells among the subsets. In PNH, each subset of lymphocytes showed a moderately higher population of cells weakly positive and a smaller population of cells strongly positive for the membrane proteins compared with those in the healthy controls. Moreover, in some PNH cases, a negative population for the proteins was found in all subsets. Thus the analysis of PI‐anchored proteins on lymphocyte subsets (especially CD8− T cells) was considered to be of diagnostic value in PNH patients who receive blood transfusion after hemolytic attack of affected erythrocytes. Furthermore, the two‐population expression of PI proteins in normal lymphocytes suggests that membrane PI protein would be a new subset marker of lymphocytes.