Reactive Lysis Research Articles

40 years of heart transplantation and the DFG‐Transregio Research Group Xenotransplantation

40 years of heart transplantation and the DFG‐Transregio Research Group Xenotransplantation

Complement inhibition by human vitronectin involves non-heparin binding domains.

Vitronectin (complement S-protein), a multifunctional glycoprotein, inhibits complement-mediated cytolysis at two identified stages of terminal complement complex (TCC) formation: blocking of C5b-7 membrane binding, and prevention of C9 polymerization. However, the functional domain(s) of vitronectin involved in these reactions remains incompletely defined. In order to identify the complement inhibition site, a 12-kD heparin binding fragment and two other internal fragments (53 kD and 43 kD) of vitronectin were isolated after cyanogen bromide (CNBr) treatment of the native molecule. Potent inhibition of guinea pig erythrocyte (GPE) reactive lysis was demonstrated with native vitronectin, total CNBr digest and the 53-kD and 43-kD fragments, but only very poorly by the heparin binding 12-kD peptide. Similarly, the 43-kD fragment blocked the binding of C5b-7 to immobilized vitronectin, whereas the 12-kD fragment had no effect. These data localize the C5b-7 binding site to a 43-kD internal region. Further characterization of the fragments was carried out in an assay which detected C9 polymerization in the presence of C5b-8. Polymerized material was separated by PAGE, detected by autoradiography and quantified after excision from the gels. Results showed that polymerization did not occur in the presence of the 53-kD and 43-kD fragments. However, the 12-kD heparin binding fragment had no effect. It is proposed that prevention of C5b-8-induced C9 polymerization resides at a site in an internal region of the vitronectin molecule.

Thyroid follicular cell function after non-lethal complement membrane attack

Terminal complement complexes have been identified around thyroid follicles in Graves' disease and Hashimoto's thyroiditis, and the concentrations of such complexes are increased in the sera of these patients, suggesting a role for complement activation and membrane attack complexes (MAC) in autoimmune thyroiditis. This has been investigated further using cultured human and rat thyroid cells. Thyrocytes were resistant to lysis by homologous complement, in contrast to the effects of heterologous (rabbit) complement. The formation of non-lethal amounts of MAC, using reactive lysis or classical pathway activation, significantly reduced cAMP production by these cells in response to thyroid-stimulating hormone (TSH) (P less than 0.01); similar effects were seen with thyroid-stimulating antibodies. Thyroid cells were able to recover rapidly from complement attack after washing and incubation for 30 min. Non-lethal MAC formation also resulted in reactive oxygen metabolite production, detected by luminol-dependent chemiluminescence in three out of five thyroid cell preparations tested. Ionomycin, but not TSH, also stimulated reactive oxygen metabolite production. These results suggest that repeated or continuous sub-lethal complement attack on thyroid cells may exacerbate hypothyroidism in Hashimoto's thyroiditis, or partially counter the effects of thyroid-stimulating antibodies in Graves' disease. Furthermore, the production of reactive oxygen metabolites in these circumstances could increase the intra-thyroidal inflammatory response; oxygen radical scavenging by anti-thyroid drugs (which are concentrated by thyrocytes) may account in part for the amelioration of thyroiditis observed with such treatment.

Expression of CD47, CD35, CD55 and CD59 on Red Cells from Patients with Warm Autoimmune Hemolytic Anemia.

Autoimmune hemolytic anemia (AIHA) is defined as an increased destruction of red cells (RBC) in the presence of anti-RBC autoantibodies. CD47 is an integrin-associated protein expressed on all cells including RBCs. Animal models show that CD47 deficiency contributes to accelerated development of AIHA, while CD35 (CR1- complement receptor 1), CD55 (decay accelerating factor), and CD59 (membrane inhibitor of reactive lysis) are complement inhibitory proteins. Using flow cytometry analysis, in this study we evaluated the expression of CD47, CD35, CD55, and CD59 on RBCs of patients with warm AIHA before any treatment had been initiated. The study population consisted of 12 patients with active AIHA [M:F = 6:6, median age: 32 yrs (3 – 73)], and 20 healthy controls [M:F = 9:11, median age: 36 yrs (25 – 71)]. Ten patients presented idiopathic AIHA while 2 subjects had secondary AIHA (systemic lupus erythematosus and non-Hodgkin's lymphoma). At presentation the median Hb level was 6.6 mg/dL (range: 2.9 to 10 mg/dL), and the median absolute reticulocyte count was 324 × 109/L (range: 215 to 756 × 109/L). At the time of the analyses, all 12 patients had a positive direct antiglobulin test (DAT), 12 (100%) had IgG on their RBCs, 5 (41.7%) had IgG plus C3, and none had C3 alone. The strength of agglutination of all positive DATs showed a strong reaction. The RBC eluates prepared by a dichloromethane technique from the cell samples were positive in all 12 patients, but the retrieved autoantibodies were pan-reactive showing no specific reactivity. The mean fluorescence intensity (MFI) of the expression of CD47, CD35 and CD55 on RBCs of AIHA patients and healthy individuals were not statistically different (CD47 = 464.4 and 464.4; CD35 = 186.8 and 194.3; CD55 = 396.9 and 381.1, respectively). Four patients with life-threatening AIHA were treated with high dose of steroids and RBC transfusions, but 3 patients evolved to death. Two patients who died presented low CD55 expression on their RBCs at diagnosis. AIHA patients showed significant lower CD59 expression on RBCs than healthy controls (MFI = 512.3 ± 28.0 and 553.7 ± 36.6, P = .03). Although CD59 expression in patients that evolved to remission was not significantly different from healthy controls (MFI = 538.5 ± 14.4 and 553.7 ± 36.6), the expression of CD59 on RBCs of 3 AHAI patients who died were significantly lower than that seen on RBCs of healthy controls (MFI = 433.6 ± 69.6 and 553.7 ± 36.6, P = .0001). Although experimental studies have suggested that CD47 has a profound influence on the severity of AIHA in mice, our preliminary data on 12 patients with AIHA did not demonstrate difference on the expression of CD47 on RBCs of patients with warm AIHA or healthy indibiduals. On the other hand, complement regulatory proteins (CD35, CD55, and CD59) may play an important role in protecting RBC destruction through the activation of complement. Our results suggest that patients with life-threatening warm AIHA may present significant CD59 deficiency on their RBCs that may increase the susceptibility of cells to complement-mediated lysis resulting in severe clinical hemolysis.

Paroxysmal Nocturnal Hemoglobinemia: A Molecular Definition of the Clinical Biology of the Disorder

Paroxysmal nocturnal hemoglobinemia (PNH), a hematopoietic stem cell disorder, arises from a somatic mutation of the phosphatidylinositol glycan-class A (PIG-A) gene. The gene product is required in the biosynthesis of a glycosylphosphatidylinositol (GPI) structure and serves as an anchor for a group of membrane proteins. The PNH cells are characterized by a total or partial lack of the GPI-anchored membrane proteins. Without this structure, intravascular hemolysis occurs due to the inability to regulate the lytic and cellstimulatory activities of complement on the membrane surface of hematopoietic cells. Two proteins, CD55-decay accelerating factor and CD59-membrane inhibitor of reactive lysis, are known to be tethered to the cell membrane by the GPI-anchor. Additionally, platelets lacking CD59 may cause venous thrombosis with possible Budd-Chiari syndrome. The development of PNH requires a hypoplastic bone marrow, somatic mutation restricted to the PIG-A gene in the stem cell, and clonal expansion of the hematopoietic stem cell pool. Received 11.9.05 | Revisions Received 12.7.05 | Accepted 12.7.05

Recombinant C345C and Factor I Modules of Complement Components C5 and C7 Inhibit C7 Incorporation into the Complement Membrane Attack Complex

Complement component C5 binds to components C6 and C7 in reversible reactions that are distinct from the essentially nonreversible associations that form during assembly of the complement membrane attack complex (MAC). We previously reported that the approximately 150-aa residue C345C domain (also known as NTR) of C5 mediates these reversible reactions, and that the corresponding recombinant module (rC5-C345C) binds directly to the tandem pair of approximately 75-residue factor I modules from C7 (C7-FIMs). We suggested from these and other observations that binding of the C345C module of C5 to the FIMs of C7, but not C6, is also essential for MAC assembly itself. The present report describes a novel method for assembling a complex that appears to closely resemble the MAC on the sensor chip of a surface plasmon resonance instrument using the complement-reactive lysis mechanism. This method provides the ability to monitor individually the incorporation of C7, C8, and C9 into the complex. Using this method, we found that C7 binds to surface-bound C5b,6 with a K(d) of approximately 3 pM, and that micromolar concentrations of either rC5-C345C or rC7-FIMs inhibit this early step in MAC formation. We also found that similar concentrations of either module inhibited complement-mediated erythrocyte lysis by both the reactive lysis and classical pathway mechanisms. These results demonstrate that the interaction between the C345C domain of C5 and the FIMs of C7, which mediates reversible binding of C5 to C7 in solution, also plays an essential role in MAC formation and complement lytic activity.

In vitro RBC exposure to Plasmodium falciparum has no effect on RBC antigen expression.

Severe malarial anaemia is a leading cause of death in African children younger than 3 years of age who are infected with Plasmodium falciparum. The pathogenesis of this anaemia is not understood. The purpose of this study was to determine if P. falciparum induces changes in RBC membranes that contribute to the immune destruction of RBCs. RBCs were collected from healthy subjects and tested using standard haemagglutination assays for 45 antigens representing 21 blood group systems/collections before and after exposure to P. falciparum, strain FVO. Lectins were used to determine whether crypt or neoantigens were expressed on the RBC membrane. Polybrene was used to detect changes in sialic acid. RBCs were cultured in vitro with and without the parasite, and blinded serologic studies were completed. CD35 (complement receptor 1), CD55 (decay-accelerating factor), CD59 (membrane inhibitor of reactive lysis) and CD47 (integrin-associated protein) flow cytometric assays were compared for infected and uninfected RBCs. The percentage of parasitaemia was determined using Giemsa-stained thin blood films. Two (Ch, Lub) of the 45 antigens had differing strengths of agglutination between infected and uninfected RBCs, but these differences were resolved with a second source of antisera. Forty-three antigens showed no significant differences in the strength of agglutination between the infected and uninfected RBCs. Lectin and polybrene testing showed no differences. CD35, CD55, CD59 and CD47 levels showed no significant differences. P. falciparum does not appear to alter the expression of classified immunogenic antigens on the RBC membrane in this in vitro system. The pathogenesis of the haemolytic episode that occurs in these children remains unclear.

Flowcytometric detection of PNH defect and response to therapy in aplastic anemia patients.

Clonal hemopoietic stem cell disorders, characterized by features of bone marrow failure, include aplastic anemia (AA) and paroxysmal nocturnal hemoglobinuria (PNH) [1]. These diseases differ in the etiopathogenesis and clinical presentations, although treatment options for both still remain a clinician’s nightmare. Damashek, way back in 1960s, first appreciated the common link between AA and PNH i.e., one disorder can evolve into the other. The ‘PNH defect’, whether de novo or secondary (arising in the background of other hematological disorders like AA) is characterized by deficiency or complete lack of more than 20 different membrane proteins, which are covalently attached to the cell membrane via a glycosyl phosphatidyl inositol (GPI) anchor [2]. The absence of GPI anchored complement regulating proteins such as membrane inhibitor of reactive lysis (MIRL or CD 59) and decay accelerating factor (DAF or CD55) is responsible for the phenotype of the disease and same feature is used for diagnostic purposes as well [2]. There is scarcity of data in the literature regarding the frequency and prognostic implications of PNH defect in AA patients [2–4]. Here we elaborate upon our experience on this subject, published earlier as a preliminary communication [4].

A gel microtyping system for diagnosis of paroxysmal nocturnal hemoglobinuria

Abstract Paroxysmal nocturnal hemoglobinuria (PNH), an acquired stem cell defect, is underdiagnosed because of its atypical symptoms in some patients and because available methods, which are time consuming and complicated, are not widely used. The hemolysis of PNH red blood cells (RBCs) is attributed to their enhanced susceptibility to complement lysis caused by a deficiency in glycosylsphos-phatidylinositol (GPI)-anchored complement regulatory membrane proteins, especially membrane inhibitor of reactive lysis (MIRL [CD59]). We evaluated the diagnostic value of a simple hemagglutination test using the gel microtyping system by comparing it with lytic tests (the Ham test and the sucrose lysis test) and with flow cytometry (FC) assessment of expression of GPI-anchored proteins (CD59 and CD55). Examining 51 blood samples from 48 patients, we found that the gel test is useful as a screening test for PNH diagnosis and can replace the Ham test and the sucrose lysis test. The threshold of the gel test is about 10 percent of defective RBCs detected by FC. It should, however, be supplemented with FC so as to analyze precisely the defective RBCs and granulocytes in patients with positive gel test results, and, in case of negative results, to detect a small clone of defective cells in atypical cases. Due to the simplicity of the gel test, its wide use can facilitate the diagnosis of PNH. Immunohematology 2002;18:9–12.

Complement-regulatory protein expression and activation of complement cascade on erythrocytes from patients with rheumatoid arthritis (RA).

It has been previously reported that the expression of the complement receptor, CR1, on erythrocytes is reduced in patients with RA and that the reduced expression of CR1 is related to disease activity. In this study we investigate the role of other regulatory proteins, i.e. decay-accelerating factor (DAF) and CD59 (membrane inhibitor of reactive lysis), in the pathogenesis of RA by checking the expression of DAF and CD59 on erythrocytes of RA patients to establish whether reduced expression of DAF and CD59 on erythrocytes could be related to increased ability of erythrocytes to activate complement in RA. Flow cytometry was used to measure the expression of DAF and CD59 on erythrocytes from RA patients as well as the deposition of C3 fragments occurring in vivo or after in vitro complement activation. Significantly reduced expression of DAF and CD59 was observed on erythrocytes of RA patients. A significant inverse relationship was observed between DAF expression and in vitro complement activation, whereas no significant relationship between CD59 and complement activation was observed. Finally, we demonstrated an inverse relationship between CH50 activity and DAF expression. Thus, determination of DAF on erythrocytes can emerge as an additional tool in the assessment of extent of complement activation in RA.

Tears contain the complement regulator CD59 as well as decay-accelerating factor (DAF).

Previous studies have shown that DAF (or CD55), a cell surface inhibitor of autologous C3 activation, is present in tears and that > 90% of the C3 convertase regulatory activity in tear fluid resides in this protein (Lass JH et al., Invest Ophth Vis Sci 1990; 31:1136-48). This study investigated whether (i) the membrane cofactor protein (MCP or CD46), an additional factor that regulates C3 activation, and (ii) the membrane inhibitor of reactive lysis (MIRL or CD59), a cell surface regulator that acts to prevent formation of the membrane attack complex, are also present in tears, and if so, are functional. Two-site immunoradiometric assays showed that MCP is present in tears at low levels (42 + 8 ng/ml, n = 8) while CD59 is present at levels (222 + 78 ng/ml, n = 14) comparable to those of DAF (325 + 289 ng/ml, n = 12). The concentrations of CD59 (i) were increased two-fold or more in closed eye tears, and (ii) were decreased in reflex tears. Western blotting showed that CD59 protein in tears migrates with an apparent mol. wt similar to membrane CD59 protein. Phenyl-Sepharose adsorption and Triton X-114 partitioning of tear CD59 as well as of tear DAF however, showed that both proteins are devoid of GPI anchors. Assays using cobra venom factor-activated human serum and guinea pig erythrocytes showed that CD59 is functionally active in inhibiting autologous C5b-9-mediated lysis and, under constitutive conditions, accounts for > 85% of the C9 inhibitory activity in tear fluid.

Interactions of IgM ABO antibodies and complement with methoxy-PEG-modified human RBCs.

RBCs modified with cyanuric chloride activated methoxy-PEG (CmPEG; 5000 Da) are less immunogenic than untreated RBCs, and their use thus may reduce the risk of alloimmunization in chronically transfused patients. To further examine the potential utility of CmPEG-RBCs, the effects of derivatization on an arm of the immune system that plays an important role in transfusion rejection-the complement system--were determined. When CmPEG-RBCs were incubated in autologous or heterologous ABO-matched serum, no classical or alternative pathway consumption was found, no C3a was generated, no cell-bound C3b or C9 was detected, and no cell lysis occurred. Cell-bound complement regulation was normal for CmPEG-RBCs, as determined by acidified serum or reactive lysis assays. CmPEG-RBCs differed from control RBCs only when incubated in ABO-mismatched serum. In that case, CmPEG modification failed to protect against ABO antibody-dependent complement-mediated lysis. Indeed, cell lysis was actually enhanced at CmPEG concentrations >1.0 mM. The enhanced lysis of CmPEG-RBCs in ABO-mismatched serum correlated with increased IgM binding and C3a generation and elevated C3b and C9 membrane deposition. While PEG modification effectively blocks non-ABO antigens, these data show that ABO matching is still required. Once ABO-matched, these modified RBCs retain great potential for the prevention of alloimmunization.

Streptococcal inhibitor of complement (SIC) inhibits the membrane attack complex by preventing uptake of C567 onto cell membranes.

Streptococcal inhibitor of complement (SIC) was first described in 1996 as a putative inhibitor of the membrane attack complex of complement (MAC). SIC is a 31 000 MW protein secreted in large quantities by the virulent Streptococcus pyogenes strains M1 and M57, and is encoded by a gene which is extremely variable. In order to study further the interactions of SIC with the MAC, we have made a recombinant form of SIC (rSIC) in Escherichia coli and purified native M1 SIC which was used to raise a polyclonal antibody. SIC prevented reactive lysis of guinea pig erythrocytes by the MAC at a stage prior to C5b67 complexes binding to cell membranes, presumably by blocking the transiently expressed membrane insertion site on C7. The ability of SIC and clusterin (another putative fluid phase complement inhibitor) to inhibit complement lysis was compared, and found to be equally efficient. In parallel, by enzyme-linked immunosorbent assay both SIC and rSIC bound strongly to C5b67 and C5b678 complexes and to a lesser extent C5b-9, but only weakly to individual complement components. The implications of these data for virulence of SIC-positive streptococci are discussed, in light of the fact that Gram-positive organisms are already protected against complement lysis by the presence of their peptidoglycan cell walls. We speculate that MAC inhibition may not be the sole function of SIC.

Expression of complement regulatory proteins on erythrocytes from patients with idiopathic focal segmental glomerulosclerosis

SUMMARY:Focal segmental glomerulosclerosis (FSGS) is a heterogeneous group of disorders with respect to aetiology, morphology, clinical course and response to treatment. The present study assessed the expression of complement receptor 1 (CR1), decay accelerating factor (DAF) and membrane inhibitor of reactive lysis (CD59) on the erythrocytes of FSGS patients using flow cytometry compared with their expression on the erythrocytes of minimal change nephrotic syndrome (MCNS) patients. Significantly reduced expression of CR1, DAF and CD59 was observed on the erythrocytes of FSGS patients compared with the reduced expression of CR1 and enhanced expression of DAF on the erythrocytes of MCNS patients. A significant inverse relationship was demonstrated between CR1 expression and proteinuria levels in FSGS patients (r = 0.55, P < 0.01). A follow‐up study of 12 patients with FSGS after immunosuppressive therapy showed that the levels of complement regulatory proteins are significantly increased when the disease goes into remission. However, in patients not responding to immunosuppressive therapy, levels of these proteins remained low. MCNS patients showed significant increases in CR1 and decreases in DAF expression during remission of the disease.

Genetic and environmental effects in paroxysmal nocturnal hemoglobinuria: this little PIG-A goes “Why? Why? Why?”

Genetic and environmental effects in paroxysmal nocturnal hemoglobinuria: this little PIG-A goes “Why? Why? Why?”

Expression of complement regulatory proteins in diffuse proliferative glomerulonephritis.

This study assessed the expression of complement receptor 1 (CR1), decay accelerating factor (DAF) and membrane inhibitor of reactive lysis (CD59) on the erythrocytes and glomerulus of diffuse proliferative glomerulonephritis (DPGN) of systemic lupus erythematosus (SLE) patients using flow cytometry and immunofluorescence techniques to elucidate their role in the pathogenesis of DPGN. Expression of CR1 on the erythrocytes and glomerulus of DPGN patients was reduced compared with expression in normal subjects. However, expression of DAF and CD59 was increased on both erythrocytes and glomerulus of DPGN patients, suggesting the generation of a protective response against complement-mediated injury.

Production and functional characterization of a soluble recombinant form of mouse CD59.

This report describes the engineering, expression, purification and functional characterization of a soluble recombinant form of murine CD59 (srMoCD59). We report the expression in Chinese hamster ovary (CHO) cells of a modified mouse CD59 cDNA that had been truncated at D-74, resulting in the loss of the glycosylphosphatidyl inositol (GPI) anchor, and containing six additional C-terminal histidines. The expressed srMoCD59 was purified from tissue culture supernatant by means of its poly-histidine tag using immobilized metal affinity chromatography. In comparison with CD59 on mouse erythrocytes, the srMoCD59 had a reduced molecular weight (18-20 000 as compared with 20-28 000 for GPI-anchored srMoCD59). The terminal complement inhibitory capacity of this soluble recombinant protein was assessed using two methods: a cobra venom factor (CVF)-triggered 'reactive-lysis' system and a C5b-7 site assay. In both assays, srMoCD59 inhibited lysis by the sera from all three species tested in the rank order mouse > rat >> human. The amount of srMoCD59 required to produce 50% inhibition of lysis in the C5b-7 site assay, using purified terminal components to develop lysis, was 10-fold less than that required in the same assay when EDTA serum was used as a source of C8 and C9, or in the CVF reactive lysis system. These data indicate that the presence of serum markedly interfered with the activity of srMoCD59 and have important implications for the use of recombinant soluble CD59 analogues as therapeutic agents in complement-mediated diseases.

Release of complement regulatory proteins from ocular surface cells in infections

Purpose. The decay accelerating factor (DAF or CD55) and the membrane inhibitor of reactive lysis (MIRL or CD59), two complement regulatory proteins that protect self cells from autologous complement-mediated injury, are attached to corneal and cqonjunctival epithelial cells by glycosylphos-phatidylinositol (GPI) anchors. We sought to 1) determine the frequency with which bacteria recovered from patients with infections of the eye elaborate factors that can remove these surface proteins from ocular cells, 2) determine the spectrum of bacteria from other sites that have similar effects, and 3) establish the time interval required for reconstitution of the two regulators. Methods. Culture supernatants of 18 ocular isolates [ P. aeruginosa (n = 3), S. marcescens (n = 1), S. epidermidis (n = 9), and S. aureus (n = 5)], and > 100 other clinical specimens isolated in the hospital's microbiology laboratory [ P. mirabilis (n = 1), S. aureus (n = 65), S. epidermidis (n = 24), B. cereus (n = 12), H. influenzae (n = 15), and Enterobacter sp. (n = 21)] were incubated at 37°C for various times with conjunctival epithelial cells, conjunctival fibroblasts or HeLa cells and the release of DAF and CD59 proteins from the surfaces of the cells analyzed by 2-site immunoradiometric assays and by Western blotting. The kinetics of recovery of DAF and CD59 expression on the cells was measured by flow cytometry. Results. DAF and/or CD59 release from the cell monolayers varied from < 5% to > 99% at as much as a 1:81 dilution of the supernatant from some bacteria. On conjunctival epithelial cells, more than 8 hr was required for 44% recovery of DAF expression and for 50% recovery of CD59 expression. Conclusions. Bacteria produce phospholipases and/or other enzymes which can efficiently remove DAF and CD59 from ocular cell surfaces. This phenomenon may correlate with their in vivo pathogenicity.

Paroxysmal Nocturnal Hemoglobinuria (Membrane Defect, Pathogenesis, Aplastic Anemia, Diagnosis)

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal disorder in which intravascular hemolysis results from the somatic mutation of the totipotent stem cells causing an intrinsic defect in red cell membrane. PNH cells lack glycosylphosphatidylinositol (GPI) anchored membrane proteins. Of these proteins absence of CD 59 (MIRL--membrane inhibitor of reactive lysis, protectin) and CD 55 (DAF--decay accelerating factor) makes the PNH cells abnormally sensitive to the lytic action of complement. The defect appears to be in the somatic mutation of the X-linked PIG-A (phosphatidylinositolglycan A class) gene which participate in an early step of GPI-anchor synthesis. PNH is characterized by recurrent life threatening venous thromboses and an intimate association with aplastic anemia (AA). It seems that PNH always coexists with bone marrow failure (BMF) (37). The possible explanation may be that some GPI-anchored proteins may be a critical target recognized by immune effector cells. PNH clones not possessing these critical GPI-anchored proteins will survive because they are selectively resistant to the autoimmune assault that eliminates most normal clones. The flow cytometry of erythrocytes using anti-CD 59 and anti-CD 59 and anti-CD 55 of granulocytes has been now introduced as a very sensitive and quantitative method of PNH diagnosis able to detect PNH cells even in normal individuals (1,54). Thus it seems now clear that we must make distinction between the detection of very occasional PNH cells in patients with BMF and PNH as a clinicohematological entity. Unfortunately, we do not know the minimal content of PNH cells required to produce clinical signs of PNH (38).

Interferon-α2a effects on complement activation and regulation in MS patients

To evaluate the treatment effect of recombinant interferon-alpha2a (rIFN-alpha2a) on complement activation and regulation in MS patients. Plasma levels of the complement activation products C3bc and terminal complement complex (TCC) and serum levels of the complement regulatory proteins, complement receptor 1, CR1 (CD35) and the membrane inhibitor of reactive lysis, protectin (CD59), were determined by enzyme-linked immunosorbent assay (ELISA) in MS patients treated with IFN-alpha2a (14 patients) or placebo (7 patients). The level of soluble CD35 decreased while the level of TCC and to a lesser degree C3bc increased in the IFN-alpha2a treated patients during the initial part of the treatment. There was also a concomitant reduction of leukocytes in the same patients. The results indicate that complement is activated during the initial phase of rIFN-alpha2a treatment. This could partly be due to a concomitant reduction in soluble CD35.