Decay-accelerating Factor Levels Research Articles

Profiling Human CD55 Transgene Performance Assist in Selecting Best Suited Specimens and Tissues for Swine Organ Xenotransplantation.

Simple SummaryThe unbalance between availability and needs of human organs has drawn researchers’ attention to xenotransplantation as an option to cope with this shortage. Pig organs have received substantial attention for being comparable to human’s; nevertheless, compatibility constrains still block clinical applications. Transgenesis of human complement regulatory proteins, including the CD55 gene and its product the decay-accelerating factor (DAF), has been proposed to overcome xenorejection. This line of research has obtained interesting results along the years; however, most works assessing the impact of this strategy for xenotransplantation are limited to analyzing gene expression and assessing resistance to conventional serum challenge hemolysis assays, which provide somewhat reduced information prior to surgery. In this work, we tried to expand the analysis of the hCD55 transgene performance beyond common practice and into a better molecular understanding of its impact in xenotransplantation. We determined hCD55 gene expression, as well as hDAF protein presence, in different organs from five transgenic pigs, comparing readings from organs worthy for transplantation and other non-valuable organs and tissues. We also assessed the ability of transgenic cells, compared to non-transgenic, to withstand hemolysis and cytolysis. Finally, we made an effort to establish potential correlations between the hCD55 mRNA and hDAF protein levels detected.Xenotransplantation of pig organs receives substantial attention for being comparable to human’s. However, compatibility constraints involving hyper-acute rejection (HAR) still block clinical applications. Transgenesis of human complement regulatory proteins has been proposed to overcome xenorejection. Pigs expressing human-CD55 have been widely tested in experimental surgery. Still, no standardized method has been developed to determine tissue expression of human decay-accelerating factor (DAF), hCD55’s product, or to predict the ability to overpass HAR. Here we describe objective procedures addressing this need. Organs and tissues from five hCD55 transgenic pigs were collected and classified according to their xenotransplantation value. The ability to overcome HAR was assessed by classical complement pathway hemolysis assays. Quantitative PCR mRNA expression and Western blot protein level studies were performed. Real-time cytotoxicity assays (RTCA) on fibroblast cultures exposed to baboon and human sera informed on longer-term rejection dynamics. While greater hCD55/DAF expression correlated with better performance, the results obtained varied among specimens. Interestingly, the individual with highest mRNA and protein levels showed positive feedback for hCD55 transcript after challenge with human and baboon sera. Moreover, hCD55 expression correlated to DAF levels in the liver, lung and intestine, but not in the heart. Moreover, we found significant correlations among valuable and non-valuable tissues. In sum, the methodology proposed allows us to characterize the hCD55 transgene functioning and performance. Moreover, the correlations found could allow us to predict hCD55/DAF expression in surrogate tissues, thus eliminating the need for direct biopsies, resulting in preservation of organ integrity before xenotransplantation.

The Role of Human Decay-Accelerating Factor in the Pathogenesis of Preterm Labor

Complement activation is thought to contribute to the pathogenesis of preterm labor (PTL). Decay-accelerating factor (DAF) is a natural complement pathway inhibitor. Our hypothesis was that DAF expression on maternal white blood cells (WBCs) in women with preterm labor is elevated compared with women with no preterm labor. Our secondary objective was to determine if differences in upregulation of DAF levels correlated with clinical outcomes. Serial blood samples were obtained from 30 patients with a clinical diagnosis of PTL and a control group of 30 pregnant individuals (same gestational age range) to determine DAF expression in peripheral WBCs in both groups. DAF expression was higher in women with PTL (less than 37 weeks) compared with the control group without PTL. Subjects with PTL who delivered before 34 weeks had less DAF expression and different kinetics of expression compared with those carrying pregnancies beyond 34 weeks. These data suggest that women with a clinical diagnosis of preterm labor have increased DAF expression on peripheral WBCs. Furthermore, it appears that failure to elevate DAF expression is associated with a risk of early premature delivery.

Role of DAF in Protecting against T-Cell Autoreactivity that Leads to Experimental Autoimmune Uveitis

To investigate the role of decay-accelerating factor (DAF), a cell surface complement regulator that recently has been linked to T-cell responses and autoimmunity in the pathogenesis of experimental autoimmune uveitis (EAU). EAU was induced in wild-type (WT) and Daf1(-/-) mice, and their disease severities, IRBP specific Th1/Th17 responses, and cytokine expression profiles were compared. In a test of the efficacy of treatment with soluble mouse DAF protein, EAU was induced in disease-susceptible B10.RIII mice, and they were treated with 0.5 mg soluble DAF protein or equal volume of PBS IP every other day. Retinal histology and IRBP-specific T-cell responses were compared after 14 days. Both EAU incidence and histopathology scores were significantly greater in Daf1(-/-) mice. There was a >10-fold greater mononuclear cell influx into the retina together with severe vasculitic lesions, retinal folding, and photoreceptor cell layer destruction. There were 5- to 7-fold greater Th1 and 3- to 4-fold greater Th17 responses against IRBP in Daf1(-/-) mice with EAU, and they expressed significantly elevated levels of GM-CSF, IL-2, IL-3, and IFN-gamma. WT B10.RIII mice that received soluble DAF protein treatments exhibited decreased IRBP-specific Th1/Th17 responses and were protected from retinal injury compared with the mice that received PBS treatments. DAF significantly influences IRBP-specific Th1 and Th17 responses and disease severity in EAU. Systemic upregulation of DAF levels could be used to suppress retinal antigen(s)-specific autoimmunity to treat autoimmune posterior uveitis.

The Role of Decay-accelerating Factor as a Receptor for Helicobacter pylori and a Mediator of Gastric Inflammation

Persistent gastritis induced by Helicobacter pylori is the strongest known risk factor for peptic ulcer disease and distal gastric adenocarcinoma, a process for which adherence of H. pylori to gastric epithelial cells is critical. Decay-accelerating factor (DAF), a protein that protects epithelial cells from complement-mediated lysis, also functions as a receptor for several microbial pathogens. In this study, we investigated whether H. pylori utilizes DAF as a receptor and the role of DAF within H. pylori-infected gastric mucosa. In vitro studies showed that H. pylori adhered avidly to Chinese hamster ovary cells expressing human DAF but not to vector controls. In H. pylori, disruption of the virulence factors vacA, cagA, and cagE did not alter adherence, but deletion of DAF complement control protein (CCP) domains 1-4 or the heavily O-glycosylated serine-threonine-rich COOH-terminal domain reduced binding. In cultured gastric epithelial cells, H. pylori induced transcriptional up-regulation of DAF, and genetic deficiency of DAF attenuated the development of inflammation among H. pylori-infected mice. These results indicate that DAF may regulate H. pylori-epithelial cell interactions relevant to pathogenesis.

Recombinant EPO therapy increases erythrocyte expression of complement regulatory proteins

Background: One of the complications of hemodialysis (HD) therapy is anemia caused by erythropoietin (EPO) deficiency. Recombinant EPO (rEPO) has been used routinely as a supplemental treatment. Erythrocyte expression of the complement regulatory proteins decay accelerating factor (DAF) and CD59 restricts complement activation and inhibits hemolysis. We hypothesized that the efficacy of rEPO treatment may be caused in part by the ability of rEPO to increase erythrocyte expression of DAF and CD59. Methods: DAF, CD59, and complement receptor 1 (CR1) levels were analyzed for a group of 95 HD patients and compared with those of a control group. To evaluate effects of discontinuation of rEPO therapy, rEPO therapy was stopped for 12 HD patients until hematocrits decreased to less than 25%. DAF and CD59 levels then were reanalyzed. Results: In the 95 HD patients, three factors correlated significantly: DAF and CD59 (r = 0.642), DAF and CR1 (r = 0.503), and CD59 and CR1 (r = 0.324), whereas no correlations were found in the group of 42 healthy controls. In the experiment in which rEPO therapy was discontinued, 8 of 12 patients reached the defined level of anemia 4 to 7 weeks after rEPO treatment had been withheld. Both DAF and CD59 levels decreased significantly after discontinuation of rEPO therapy (P < 0.01). DAF and CD59 levels increased in all 8 patients after rEPO treatment was reinitiated (P < 0.01), and CR1 levels increased in 5 of 8 patients. Four of 12 patients showed no evidence of anemia after discontinuation of rEPO treatment. In these patients, DAF, CD59, and CR1 levels did not change before or after withholding rEPO therapy. Conclusion: One of the mechanisms mediating the efficacy of EPO therapy is increased DAF and CD59 expression. Am J Kidney Dis 41:179-185. © 2003 by the National Kidney Foundation Inc.

Decay-accelerating factor (DAF) in stool specimens as a marker of disease activity in patients with ulcerative colitis (UC).

Colonic epithelial cells of patients with UC express DAF in relation to the severity of mucosal inflammation. The aim of this study was to determine whether this factor in stool could be used as a marker of disease activity in UC patients. Stool DAF was measured by use of an immunoassay in 181 stool specimens obtained from 55 patients with UC of various levels of disease activity. Stool DAF concentrations in patients whose UC was active (0.0-785.6 ng/g stool; median 47.1 ng/g; n = 115) were significantly higher than concentrations in patients whose disease was inactive (0.0-48.6 ng/g; median 0.0 ng/g; n = 66) (P < 0.0001). Values in active UC patients also were higher than those in control patients with diarrhoea (0.0-30.0 ng/g; median 0.0 ng/g; n = 26) (P < 0.0001) and in control subjects without apparent colorectal disease (0-20.4 ng/g; median 0.0 ng/g; n = 44) (P < 0.0001). The elevated levels of stool DAF obtained from UC patients in relapse declined markedly in specimens collected after the disease went into remission following medical therapy. Stool DAF levels correlated with the severity of endoscopic and histological findings and the degree of DAF expression on the colonic epithelia. Our results suggest that the measurement of stool DAF is useful as a non-invasive means of monitoring intestinal disease activity in patients with UC.

Evaluation of urinary decay accelerating factor and CD59 in renal damage

Decay accelerating factor (DAF) and CD59 (protectin) are complement regulatory proteins that can be detected in soluble form in urine. We studied the relationship between renal disease and the mechanisms involved in the urinary excretion of complement regulatory proteins. Urine samples were obtained from 143 patients with renal disease and 61 individuals with normal renal function, who served as control subjects. As a model of limited tubular injury, we also studied the urine of 5 patients who were being treated with cisplatin for lung cancer; samples were collected before administration of the chemotherapeutic agents (day 0) and every morning during the observation period (15 days). Urinary DAF, CD59, and SC5b-9 (a complement component) were measured by enzyme-linked immunosorbent assay, using monoclonal antibodies. In the patients with renal disease, urinary DAF and CD59 levels were higher than in healthy control subjects (P<0.001). The correlations between urinary DAF and CD59 levels were significant in patients with renal disease and healthy individuals (P<0.001). Urinary SC5b-9 was not correlated with either urinary DAF or CD59 in patients with IgA nephropathy. In the patients with lung cancer, urinary DAF and CD59 were elevated after the administration of cisplatin. This was accompanied by an increase in the secretion of urinaryN-acetyl-β-d-glucosaminidase and β2-microglobulin, both of which are markers for tubular injury. These results suggest that elevated levels of urinary DAF and CD59 are related to renal disease, as well as to the limited tubular injury associated with cisplatin treatment.

Dr(a-) polymorphism of decay accelerating factor. Biochemical, functional, and molecular characterization and production of allele-specific transfectants.

The Dra antigen belongs to the Cromer-related blood group system, a series of antigens on decay accelerating factor (DAF), a glycosyl-phosphatidylinositol-anchored membrane protein that protects host cells from complement-mediated damage. We studied the rare inherited Dr(a-) phenotype to ascertain the associated biochemical and functional changes in DAF and to characterize the basis for this polymorphism. Radioimmunoassay assay and flow cytometric analysis of Dr(a-) erythrocytes demonstrated 40% of normal surface expression of DAF but normal levels of several other glycosyl-phosphatidylinositol-anchored proteins, distinguishing this phenotype from that of paroxysmal nocturnal hemoglobinuria. Western blots confirmed this reduced DAF expression and indicated a slightly faster mobility of the molecule on SDS-PAGE. Despite the reduced DAF expression, Dr(a-) erythrocytes functioned normally in the complement lysis sensitivity assay. Utilization of the polymerase chain reaction to amplify mononuclear cell genomic DNA from three unrelated Dr(a-) individuals demonstrated that a point mutation underlies the Dr(a-) phenotype: a C to T change in nucleotide 649 resulting in a serine165 to leucine change. This defines the Drb allele of DAF, which can be distinguished from Dra by a Taq I restriction fragment length polymorphism. We created transfected Chinese hamster ovary cell lines expressing either the Dra or the Drb allelic form of DAF. These allele-specific transfectants were tested by inhibition of hemagglutination or flow cytometry and confirmed the specificity of anti-Dra alloantisera. The allele-specific transfectants could form the basis of a new serological approach to immunohematology.

Phorbol esters increase synthesis of decay-accelerating factor, a phosphatidylinositol-anchored surface protein, in human endothelial cells.

A number of cell-surface proteins are anchored by a phosphatidylinositol (PI)-glycan moiety. These proteins can be released by PI-specific phospholipases C (PI-PLC). Decay-accelerating factor (DAF) is such a cell-surface protein that protects cells from inadvertent complement attack by binding to and inactivating C3 and C5 convertases. We have studied the regulation of DAF synthesis in human umbilical vein endothelial cells (HUVEC), a cell that has the highest level of surface DAF among those human cells that have been studied. HUVEC DAF was measured by immunoradiometric assay of detergent extracts and of cell supernatants after treatment of cells with a bacterial (Bacillus thuringiensis) PI-PLC. Eighty percent of the HUVEC DAF (4 to 8 x 10(5) molecules/cell) was released by exogenously added PI-PLC, indicating that it is predominantly PI-anchored. The level of PI-PLC-sensitive HUVEC DAF was increased three- to fourfold by overnight treatment of cultures with the protein kinase C activators, PMA (1 to 10 nM), phorbol-12,13-dibutyrate (10 to 100 nM), and teleocidin A (1 to 10 nM) under conditions where cell number, protein, and lactate dehydrogenase remain unchanged. This DAF synthesis was blocked by the protein kinase C inhibitor K-252a in a dose-dependent manner (ED50 = 0.06 microM). The biologically inactive phorbols, 4-alpha-phorbol-12 myristate-13-acetate (1 microM) and 4-alpha-phorbol-12, 13-didecanoate (1 microM) did not increase DAF levels. The newly expressed DAF in PMA-stimulated cells was still largely PI-anchored. In contrast, another PI-anchored protein, alkaline phosphatase, was not altered by PMA treatment, demonstrating that the PMA effect is not uniform among all surface proteins. The increased expression of DAF only was evident 8 h after PMA addition and was blocked by the RNA and protein synthesis inhibitors, actinomycin D and cycloheximide, indicating that both transcription and translation are required for DAF synthesis induced by phorbol esters. It is concluded that protein kinase C activators cause selective induction of endothelial cell DAF and that DAF synthesis involves protein kinase C activation.

Heightened complement sensitivity of acquired immunodeficiency syndrome lymphocytes related to diminished expression of decay-accelerating factor.

Although the human immunodeficiency virus can induce cytopathic changes in human lymphocytes in vitro, the mechanism(s) underlying progressive lymphopenia in patients with AIDS and AIDS-related complex has not been elucidated. To investigate this issue, peripheral blood lymphocytes of AIDS and AIDS-related complex patients and healthy control subjects were examined for their ability to resist homologous complement-mediated lysis. Upon sensitization with monoclonal antibodies to major histocompatibility complex class I antigen, as much as 48% lysis of patients' cells was observed in as little as a 1:32 dilution of human serum compared to 18 +/- 8% (mean +/- SD) lysis of controls' cells even in a 1:8 dilution of human serum. To investigate the mechanism of the abnormal complement sensitivity, AIDS and AIDS-related complex cells were analyzed for expression of decay-accelerating factor (DAF), a complement regulatory protein that functions intrinsically in blood cell membranes to prevent complement activation on their surfaces. Flow cytometric assays using anti-DAF monoclonal antibodies demonstrated that patients' lymphocytes and monocytes were DAF-deficient, in contrast to their polymorphonuclear leukocytes, which showed normal DAF levels. Expression of DAF was diminished on CD4+ as well as CD8+ T-lymphocyte subpopulations as opposed to expression of CD3, which was comparable in patients and controls. Incubation of normal lymphocytes with anti-DAF monoclonal antibodies or phosphatidylinositol-specific phospholipase C, an enzyme that cleaves DAF, enhanced lysis. Conversely, reconstitution of patients' cells with exogenous DAF reduced their lysis. The findings of heightened complement sensitivity and DAF deficiency of patients' lymphocytes in vitro suggest the possibility that the DAF deficit may contribute to the progressive lymphopenia of AIDS in vivo.

Decay‐accelerating factor (DAF) on the blood cell membranes in patients with paroxysmal nocturnal haemoglobinuria (PNH): measurement by enzyme‐linked immunosorbent assay (ELISA)

We developed a quantitative enzyme-linked immunosorbent assay (ELISA) for decay-accelerating factor (DAF) on blood cell membranes using monoclonal anti-DAF antibodies. DAF is an integral membrane protein of several blood cells. It regulates the C3 and C5 convertase of the classical and alternative pathways of complement activation. It is partially or completely deficient in the membranes of blood cells of patients with paroxysmal nocturnal haemoglobinuria (PNH). The ELISA we developed for DAF measurement indicated a reliable range of measurement from 2.25 to 11.25 ng of DAF. In particular, ELISA proved to be a technically simple method and its sensitivity was enhanced by using avidin-biotin complex. In this study, DAF levels in extracts of erythrocytes from 30 healthy donors and in extracts of PMN and platelets from 15 healthy donors were measured by ELISA. The DAF content of blood cells from eight patients with PNH and erythrocytes from 13 patients with anaemia were also measured. The DAF levels of normal erythrocytes, PMN and platelets were 3110 +/- 960, 28,000 +/- 13,900 and 3100 +/- 1370 (mean +/- SD) molecules/cell, respectively. In general, the DAF content of PNH cells was below the normal range, although it was within the normal range in some cases of PNH. The DAF levels of PNH-I and -II erythrocytes were estimated from the ratio of PNH-I, -II and -III erythrocytes. And, in four cases of PNH, the DAF levels of PNH-I erythrocytes separated by acidified serum lysis were measured by ELISA. In most cases of PNH, DAF was found to be partially deficient in PNH-I and PNH-II erythrocytes.

Identification of the complement decay-accelerating factor (DAF) on epithelium and glandular cells and in body fluids.

Decay-accelerating factor (DAF) is a 70 kD membrane regulatory protein that prevents the activation of autologous complement on cell surfaces. Using immunohistochemical methods and a radioimmunometric assay based on mAbs to DAF, we found large amounts of membrane-associated DAF antigen on the epithelial surface of cornea, conjunctiva, oral and gastrointestinal mucosa, exocrine glands, renal tubules, ureter and bladder, cervical and uterine mucosa, and pleural, pericardial and synovial serosa. Additionally, we detected soluble DAF antigen in plasma, tears, saliva, and urine, as well as in synovial and cerebrospinal fluids. While plasma, tear, and saliva DAF are larger than erythrocyte (Ehu) membrane DAF by Western blot analysis, urine DAF is slightly smaller (67,000) in Mr. Unlike purified Ehu DAF, however, urine DAF is unable to incorporate into the membrane of red cells. Although its inhibitory activity on the complement enzyme C3-convertase is lower than that of Ehu DAF, it is comparable to that of serum C4 binding protein (C4bp). Biosynthetic studies using cultured foreskin epithelium and Hela cells disclosed DAF levels (approximately 2 X 10(5) molecules/cell) exceeding those on blood cells. In addition, these studies revealed the synthesis of two DAF species, one with apparent Mr corresponding to that of epithelial cell membrane DAF and the other to urine DAF, suggesting that the urine DAF variant arises from adjacent epithelium. The function of DAF in body fluids is unknown, but the observation that urine DAF has C4bp-(or factor H-)like activity shows that it could inhibit the fluid phase activation of the cascade.

Distribution of decay-accelerating factor in the peripheral blood of normal individuals and patients with paroxysmal nocturnal hemoglobinuria.

Decay-accelerating factor (DAF) is a 70,000 Mr protein that has been isolated from the membrane of red cells. The function of DAF is to inhibit the assembly of amplifying enzymes of the complement cascade on the cell surface, thereby protecting them from damage by autologous complement. We raised monoclonal antibodies to DAF and used them to study its distribution in cells from the peripheral blood of normal individuals and of patients with paroxysmal nocturnal hemoglobinuria (PNH), a disease characterized by the unusual susceptibility of red cells to the hemolytic activity of complement. The results of immunoradiometric assays and of fluorescence-activated cell sorter analysis showed that DAF was present not only on red cells but was widely distributed on the surface membrane of platelets, neutrophils, monocytes, and B and T lymphocytes. By Western blotting, we observed small but consistent differences in the Mr of DAF from the membranes of various cell types. Quantitative studies showed that phagocytes and B lymphocytes, which presumably enter more frequently in contact with immune complexes and other potential activators of complement, had the highest DAF levels. As previously reported by others, the red cells from PNH patients were DAF deficient. When the patients' red cells were incubated in acidified serum (Ham test), only the DAF-deficient cells were lysed. In addition, we detected defects in DAF expression on platelets and all types of leukocytes. The observed patterns of DAF deficiency in these patients were consistent with the concept that the PNH cells were of monoclonal origin. In one patient, abnormal and normal cells were found only in the erythroid, myeloid, and megakaryocytic lineages. In two other patients, the lymphocytes were also DAF deficient, suggesting that a mutation occurred in a totipotent stem cell. It appears, therefore, that the lesion leading to PNH can occur at various stages in the differentiation of hematopoietic cells.