FLAER (Proaerolysin)

FLAER is a unique protein that binds tightly and specifically to mammalian glycol-phosphatidylinositol (GPI) anchored proteins on the cell surface. In healthy individuals, FLAER binds to nearly all GPI-expressing human lymphocytes, monocytes, and granulocytes. However, in patients with Paroxysmal Nocturnal Hemoglobinuria (PNH), white blood cells lose the expression of GPI-anchored cell-surface proteins, resulting in FLAER failing to bind to lymphocytes, monocytes, and granulocytes (1) .
Detection of PNH clones can be achieved through flow cytometry using fluorescently labeled antibodies to other GPI-linked proteins such as CD59 and CD55. However, these antibodies have low binding affinity to GPI-anchored surface antigens, often leading to false-negative results. Due to FLAER's high binding affinity to the GPI anchor itself, only PNH cells, which lack the GPI-anchored surface protein, will be negative. This provides confirmatory results for the presence of PNH clones (2) .