Flow cytometric analysis of erythrocytes in paroxysmal nocturnal hemoglobinuria reveals superiority of CD59 as a diagnostic marker compared to CD55.
BACKGROUND
Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal stem cell disorder characterized by complement-mediated hemolysis due to reduced expression of glycosyl phosphatidylinositol-anchored complement deactivating proteins such as CD55 and CD59 on RBC. Flow cytometric analysis of CD55 and CD59 expression by RBC is a reliable tool for the diagnosis of PNH.


OBJECTIVE
Detection and quantification of PNH clone and comparison of the relative role of CD55 and CD59 expression by RBC in the diagnosis of PNH.


METHODS
Flow cytometric analysis of RBC was performed in blood samples of 239 patients by direct immunofluorescence using monoclonal anti-CD55 and anti-CD59 antibodies. CD55 and CD59 expressions by RBC were compared in 54 cases in which PNH clones were detected.


RESULTS
Out of 54 cases, 85% and 72% revealed CD59 and CD55 negative populations, respectively. Various combinations of type II and III erythrocytes could be identified in all cases having CD59 deficient RBC. In contrast, distinct populations of CD55-deficient RBC were seen in only 33% cases. In the remaining (67%) cases, CD55 negative RBC caused sloping of the ascending limb of the histogram resulting in difficulties in interpretation. Fifteen percent cases had false CD55-deficient RBC and in 23% cases anti-CD55 antibody failed to identify PNH clones which were detected by CD59.


CONCLUSIONS
CD59 is a better marker for the diagnosis of PNH. Although CD55 negativity supported the diagnosis of PNH in cases with CD59-deficient RBC, its role as an independent diagnostic marker for PNH is questionable due to its lower sensitivity and specificity.
Hematopathology and Flow Cytometry sections, Super Religare Laboratories, Mumbai, India.
Prashant
P
Tembhare
Manisha
M
Ramani
Keerti
K
Syed
Amar Das
AD
Gupta
D000293:Adolescent; D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal; D015415:Biomarkers / Q000097:blood; D018958:CD55 Antigens / Q000032:analysis*; D018957:CD59 Antigens / Q000032:analysis*; D004912:Erythrocytes / Q000737:chemistry*; D005260:Female; D005434:Flow Cytometry / Q000379:methods; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D006457:Hemoglobinuria, Paroxysmal / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D055815:Young Adult
D000911:Antibodies, Monoclonal; D015415:Biomarkers; D018958:CD55 Antigens; D018957:CD59 Antigens; C051590:CD59 protein, human