FLOW CYTOMETRIC ANALYSIS OF HOMOLOGOUS RESTRICTION FACTOR 20KD (HRF20) EXPRESSION ON PROGENY CELLS DURING DIFFERENTIATION FROM HEMATOPOIETIC PROGENITORS IN PAROXYSMAL-NOCTURNAL HEMOGLOBINURIA

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired clonal disor der with a deficiency of glycosyl-phosphatidylinositol (GPI) anchored proteins, Homologous restriction factor 20KD (HRF20, CD59) is a GPI-an chored and major complement-regulatory protein which plays a key role in the haemolytic mechanism of PNH, We examined the differentiation st age at which the PNH abnormality occurs, by means of now cytometric an alysis of HRF20 expression, Non-phagocytic mononuclear marrow cells we re labelled with anti-HRF20 monoclonal antibody and sorted into either HRF20-negative or -positive fractions, The sorted cells were cultured in methylcellulose and their progeny in the colonies or bursts were a nalysed for HRF20 expression. All colonies and bursts from HRF20-negat ive fractions remained negative, whereas those from HRF20-positive fra ctions were either positive or negative, The possibility of a sorting error was excluded, because the secondary colonies from the HRF20 posi tive primary colonies consisted of both positive and negative progeny, These results suggest that there are several stages during differenti ation from early progenitors to mature cells, at which the PNH abnorma lity becomes manifest.