AA results from an autoimmune attack on stem cells. Paroxysmal nocturnal hemoglobinuria (PNH) can arise de novo or evolve from AA. PNH is caused by a PIG-4 gene mutation resulting in loss of glycosylphosphatidylinositol (GPI) anchored protein s. We developed 2 novel assays to detect PNH cells using the pore-forming toxin, aerolys n (Brodsky et al, Blood 1999;93:1749-56). The GPI-anchor is the receptor for aerolysii; hence, PNH cells are resistant to the lytic properties of the toxin. A red cell assay in whii h cells are stained with anti-CD59 before and after exposure with aerolysin was shown to detect 0.004% PNH cells. Fluorescent proaerolysin varient (FLAER) binds the GP[1-anchor without forming channels. The FLAER assay directly assesses the biochemical consequence of PIGA mutations, global loss of GPl-anchors, rather than the absence of individual surrogate proteins, and can reliably detect 0.5% PNH cells. The improved sensitivity of these aerolysin-based assays was used to examine the relationship between AA and PNH. Red cells from 23 newly diagnosed, untreated AA patients (pts), 10 PNH pts, 11 MDS pts, 6 normals (N) and 9 disease controls (DC) were studied with anti-CD59 before and after aerolysin exposure. Although all PNH pts were positive in the red cell assay, none of the MDS, N, or DC pts were positive before or after enrichment in aerolysin. In contrast, although only 1/23 AA pts had detectable PNH red cells before exposure to aerolysin, 14 (61 %) had detectable PNH red cells after enrichment in aerolysin. We also used FLAER to detect PNH granulocytes in 18 newly diagnosed, untreated AA pts, 8 PNH pts, 9 MDS pts, 5 N, and 9 DC. All PNH pts had 60% GPI-anchor deficient granulocytes; none of the N, MDS or DC subjects had GPI-deficient granulocytes. However, 12 of 18 AA pts (67%) had GPI-anchor deficient granulocytes with FLAER. Concordance between the 2 assays exceeded 98%. Clonality is an early event in AA and suggests that AA and PNH represent different responses to stem cell insults. The same stem cell insult could lead to either a predominant autoimmune attack (AA) and/or a clonal disorder (PNH or MDS). Over time, the slowly proliferating clone (PNH, MDS) could become dominant. In some patients, stem cell injury may result in the simultaneous appearance of both autoimmune marrow suppression and clonality (PNH/AA overlap or hypoplastic MDS). Aerolysin-based assays should be useful in determining the clinical significance of occult PNH populations in AA over time.
|Original language||English (US)|
|Issue number||11 PART I|
|State||Published - Dec 1 2000|
ASJC Scopus subject areas
- Cell Biology