Affected erythrocytes of patients with paroxysmal nocturnal hemoglobinuria are deficient in the complement regulatory protein, decay accelerating factor.

Abstract

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired-defect of bone marrow stem cells in which the affected clones produce erythrocytes (also granulocytes and platelets) with membranes that are abnormally sensitive to complement-mediated lysis. Abnormal erythrocytes (E) from patients with PNH (PNH-E) are 3-5 times more sensitive (type II PNH-E) or 15-25 times more sensitive (type Im PNH-E) to lysis in vitro by human complement than normal -E from unaffected individuals and the functionally normal E that arise from unaffected clones in PNH patients (type I PNH-E). After complement activation by either the classical or alternative pathway, abnormal amounts of C3b are deposited on the membranes of PNH-E compared with normal E, suggesting that the PNH-E membrane cannot regulate the events responsible for C3b deposition. Two proteins that decrease the stability of the classical and alternative pathway C3 convertases on target cells have been isolated from normal human E stroma: the 70,000 Mr decay accelerating factor of stroma (DAF) and the 250,000 Mr C3b receptor (C3bR pathway (8, 9), by the alternative pathway (10, 11), or by acid treatment of C5 that results in subsequent formation of the lytic complex of complement proteins, C5-9 (12, 13). The relative contribution of each of these pathways to the lysis of PNH-E in vivo is not known.With equivalent amounts of isohemagglutinin sensitization, normal E, type II PNH-E, and type III PNH-E activate the same amount of C1 and bind equivalent amounts of C4b, but 6 times more membrane-bound C3b is deposited on PNH-E than on normal E (14). The classical C3 convertase, C4b,2a, loses its ability to cleave C3 enzymatically and deposit C3b when the C2a subunit "spontaneously" dissociates from the membrane-bound C4b subunit (15, 16). The increased ratio of C3b/ C4b bound to PNH-E suggests that these cells may lack a regulatory mechanism for C3 convertase activity.Two proteins that regulate complement C3 convertases on target cells have been isolated from the membranes of normal E: the 70,000 M, decay accelerating factor of stroma (DAF) (17, 18) and the 250,000 Mr C3b receptor (C3bR) (19,20). When DAF and the C3bR are solubilized and isolated, each can cause the accelerated decay of both membrane-bound classical (C4b,2a) and properdin-stabilized alternative complement (C3b, Bb) C3 convertases; DAF has preferential activity for the C4b,2a convertase and C3bR for the C3b,Bb convertase (18). The availability of an antiserum to each of these moieties allowed the direct determination of their presence or absence on PNH-E. MATERIALS AND METHODSThe following reagents were-obtained as noted: acrylamide, bisacrylamide, temed, 2-mercaptoethanol, NaDodSO4, hydroxyapatite, and nitrocellulose paper from Iodogen (1,3,4,

Decreased expression of FcγRIII mRNA in leukemic granulocytes

“…This protein is also a Pltailed protein like the Fc?'RIII. The lowered expression of these two Pldinked proteins in CML seems to follow the trend that is observed with respect to the decreased expression of Pl-linked proteins, leukocyte alkaline phosphatase, acetylcholine esterase, FcyRIII and dccay acceleration factor in PNH patients [13][14][15][16]. In the latter disorder however, the lowered expression of these proteins is believed to be associ~te£ -,,.…”

A functional SNP in the regulatory region of the decay-accelerating factor gene associates with extraocular muscle pareses in myasthenia gravis

“…40,41 Moreover, a few rare individuals have been identified as having the Cromer phenotype of blood group antigens (INAB), in whom polymorphisms within the DAF gene result in low or no DAF expression. 42 These individuals are otherwise well, although some have developed inflammatory bowel disease.…”

Prostaglandin E2 Regulates the Complement Inhibitor CD55/Decay-accelerating Factor in Colorectal Cancer

“…Conversely, loss of DAF expression has been linked to paroxysmal nocturnal hemoglobinuria, a condition characterized by complement-mediated hemolysis through autologous complement attack (53,54). Hyperacute rejection in xenografts is mediated in part through reduced activity of complement regulatory proteins, including CD59, membrane cofactor protein, and DAF (55).…”