Paroxysmal nocturnal hemoglobinuria erythrocytes are of two distinct types: positive or negative for acetylcholinesterase.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired disorder. Erythrocytes isolated from PNH patients show increased sensitivity to complement and decreased acetylcholinesterase (AChE) activity. In this study, indirect immunofluorescence analysis of a monoclonal antibody specific for a surface epitope of human erythrocyte AChE is used to quantitate the content of this enzyme at the single-cell level. Flow-cytofluorimetric analysis of erythrocytes from normal donors indicates that all erythrocytes contain detectable levels of the surface epitope with a strong correlation between cell size and enzyme content. In contrast, erythrocytes from PNH patients show two distinct populations of erythrocytes; namely, those containing a normal content of AChE and a second population containing no detectable AChE. The AChE-negative population of cells is quantitatively complement-sensitive. These data support suggestions that PNH is a clonal disorder resulting in two distinct types of circulating erythrocytes. The abnormal clone produces cells that are both surface-AChE-negative and complement-sensitive. In addition, the method described provides an attractive alternative for the diagnosis and quantitative evaluation of abnormal erythrocytes in PNH patients.