Isolation and characterization of a membrane protein from rat erythrocytes which inhibits lysis by the membrane attack complex of rat complement

Anti-C5a complementary peptide mitigates zymosan-induced severe peritonitis with fibrotic encapsulation in rats pretreated with methylglyoxal

In a previous study of fungal peritoneal injury in peritoneal dialysis patients, complement (C)-dependent pathological changes were developed in zymosan (Zy)-induced peritonitis by peritoneal scraping. However, the injuries were limited to the parietal peritoneum and did not show any fibrous encapsulation of the visceral peritoneum, which differs from human encapsular peritoneal sclerosis (EPS). We investigated peritoneal injury in a rat model of Zy-induced peritonitis pretreated with methylglyoxal (MGO) instead of scraping (Zy/MGO peritonitis) to clarify the role of C in the process of fibrous encapsulation of the visceral peritoneum. Therapeutic effects of an anti-C5a complementary peptide, AcPepA, on peritonitis were also studied. In Zy/MGO peritonitis, peritoneal thickness, fibrin exudation, accumulation of inflammatory cells, and deposition of C3b and C5b-9 with loss of membrane C regulators were increased along the peritoneum until day 5. On day 14, fibrous encapsulation of the visceral peritoneum was observed, resembling human EPS. Peritoneal injuries and fibrous changes were significantly improved with AcPepA treatment, even when AcPepA was administered following injection of Zy in Zy/MGO peritonitis. The data show that C5a might play a role in the development of encapsulation-like changes in the visceral peritoneum in Zy/MGO peritonitis. AcPepA might have therapeutic effects in fungal infection-induced peritoneal injury by preventing subsequent development of peritoneal encapsulation.

Molecular cell biology of complement membrane attack

The membrane attack complex (MAC) is the pore-forming toxin of the complement system, a relatively early evolutionary acquisition that confers upon complement the capacity to directly kill pathogens. The MAC is more than just a bactericidal missile, having the capacity when formed on self-cells to initiate a host of cell activation events that can have profound consequences for tissue homeostasis in the face of infection or injury. Although the capacity of complement to directly kill pathogens has been recognised for over a century, and the pore-forming killing mechanism for at least 50 years, there remains considerable uncertainty regarding precisely how MAC mediates its killing and cell activation activities. A recent burst of new information on MAC structure provides context and opportunity to re-assess the ways in which MAC kills bacteria and modulates cell functions. In this brief review we will describe key aspects of MAC evolution, function and structure and seek to use the new structural information to better explain how the MAC works.

Depression of Complement Regulatory Factors in Rat and Human Renal Grafts Is Associated with the Progress of Acute T-Cell Mediated Rejection

Background

The association of complement with the progression of acute T cell mediated rejection (ATCMR) is not well understood. We investigated the production of complement components and the expression of complement regulatory proteins (Cregs) in acute T-cell mediated rejection using rat and human renal allografts.

Methods

We prepared rat allograft and syngeneic graft models of renal transplantation. The expression of Complement components and Cregs was assessed in the rat grafts using quantitative real-time PCR (qRT-PCR) and immunofluorescent staining. We also administered anti-Crry and anti-CD59 antibodies to the rat allograft model. Further, we assessed the relationship between the expression of membrane cofactor protein (MCP) by immunohistochemical staining in human renal grafts and their clinical course.

Results

qRT-PCR results showed that the expression of Cregs, CD59 and rodent-specific complement regulator complement receptor 1-related gene/protein-y (Crry), was diminished in the rat allograft model especially on day 5 after transplantation in comparison with the syngeneic model. In contrast, the expression of complement components and receptors: C3, C3a receptor, C5a receptor, Factor B, C9, C1q, was increased, but not the expression of C4 and C5, indicating a possible activation of the alternative pathway. When anti-Crry and anti-CD59 mAbs were administered to the allograft, the survival period for each group was shortened. In the human ATCMR cases, the group with higher MCP expression in the grafts showed improved serum creatinine levels after the ATCMR treatment as well as a better 5-year graft survival rate.

Conclusions

We conclude that the expression of Cregs in allografts is connected with ATCMR. Our results suggest that controlling complement activation in renal grafts can be a new strategy for the treatment of ATCMR.

Rat adipose tissue-derived stem cells attenuate peritoneal injuries in rat zymosan-induced peritonitis accompanied by complement activation

BACKGROUND AIMS

In patients receiving peritoneal dialysis, fungal or yeast peritonitis has a poor prognosis. In rat peritoneum with mechanical scraping, severe peritonitis can be induced by zymosan, a component of yeast (Zy/scraping peritonitis). Administration of rat adipose tissue-derived stromal cells (ASCs) potentially can improve several tissue injuries. The present study investigated whether rat ASCs could improve peritoneal inflammation in Zy/scraping peritonitis.

METHODS

Rat ASCs were injected intraperitoneally on a daily basis in rats with Zy/scraping peritonitis.

RESULTS

Peritoneal inflammation accompanied by accumulation of inflammatory cells and complement deposition was suppressed by day 5 after injection of rat ASCs. The peritoneal mesothelial layer in Zy/scraping peritonitis with rat ASC treatment was restored compared with the peritoneal mesothelial layer without rat ASC treatment. Injected rat ASCs co-existed with mesothelial cells in the sub-peritoneal layer. In vitro assays showed increased cellular proliferation of rat mesothelial cells combined with rat ASCs by co-culture assays, confirming that fluid factors from rat ASCs might play some role in facilitating the recovery of rat mesothelial cells. Hepatocyte growth factor was released from rat ASCs, and administration of recombinant hepatocyte growth factor increased rat mesothelial cell proliferation.

CONCLUSIONS

Because the peritoneal mesothelium shows strong expression of membrane complement regulators such as Crry, CD55 and CD59, restoration of the mesothelial cell layer by rat ASCs might prevent deposition of complement activation products and ameliorate peritoneal injuries. This study suggests the therapeutic possibilities of intraperitoneal rat ASC injection to suppress peritoneal inflammation by restoring the mesothelial layer and decreasing complement activation in fungal or yeast peritonitis.

Anti-C5a complementary peptide ameliorates acute peritoneal injury induced by neutralization of Crry and CD59

In peritoneal dialysis (PD) therapy, physical stresses such as exposure to peritoneal dialysate, catheter trauma, and peritonitis may induce peritoneal injury that can prevent continued long-term PD therapy. Therefore, protection of the peritoneum is an important target to enable long-term PD therapy in patients with end-stage renal disease. We previously showed that neutralization of the membrane complement regulators (CRegs) Crry and CD59 in rat peritoneum provokes development of acute peritoneal injury due to uncontrolled complement activation. C5a is a key effecter molecule of the complement system released during acute inflammation. Control of C5a has been proposed as a strategy to suppress inflammatory reactions and, because peritoneal injury is accompanied by inflammation, we hypothesized that C5a targeted therapy might be an effective way to suppress peritoneal injury. In the present study we used an established acute peritonitis model induced by neutralization of CRegs to investigate the effects on acute peritoneal injury of inhibiting C5a. Intravenous administration of an anti-C5a complementary peptide (AcPepA) up to 4 h after induction of injury significantly and dose-dependently prevented accumulation of inflammatory cells and reduced tissue damage in the model, accompanied by decreased C3b deposition. We show that C5a contributed to the development of peritoneal injury. Our results suggest that C5a is a target for preventing or treating peritoneal injury in patients undergoing prolonged PD therapy or with infectious complications.

Membrane complement regulators protect against fibrin exudation increases in a severe peritoneal inflammation model in rats

Peritonitis and the rare sequela of encapsulating peritoneal sclerosis (EPS) are serious problems in patients on peritoneal dialysis therapy. Chronic and persistent peritoneal injuries may be a risk factor of EPS. We previously reported that a chronic, proliferative peritonitis developed when zymosan was administered intraperitoneally following scraping injury of rat peritoneum (Mizuno M, Ito Y, Hepburn N, Mizuno T, Noda Y, Yuzawa Y, Harris CL, Morgan BP, Matsuo S. J Immunol 183: 1403–1412, 2009). Peritoneal membrane complement regulators (CRegs), especially Crry and CD59, protected from injury by inhibiting local complement activation, suggesting that CRegs play important roles in maintaining homeostasis in rat peritoneum. Here, we investigated roles of complement in the development of EPS by neutralizing CReg function with monoclonal antibodies (MAbs). Proliferative peritonitis was induced by scraping the peritoneum, followed by daily intraperitoneal administration of zymosan. When either Crry or CD59 alone was neutralized by MAb, the tissue injuries were not significantly changed compared with rats without neutralizing MAb. When both Crry and CD59 were neutralized in this model, severe fibrin exudation was observed on the peritoneal surface on day 5, accompanied by inflammatory cell infiltration, resembling the early stages of development of EPS. Dense peritoneal deposition of C3 fragments and membrane attack complex were observed, along with the fibrin exudates. Intravenous administration of cobra venom factor, which profoundly activates complement, further enhanced these pathological changes. Our results show that complement activation in injured peritoneum drives peritoneal inflammation, and that enhancement of complement activation by inhibiting CReg and/or enhancing systemic activation contributes to the initiation of EPS; therefore, anti-complement agents might be of therapeutic value in humans for the treatment of EPS.

Zymosan, but Not Lipopolysaccharide, Triggers Severe and Progressive Peritoneal Injury Accompanied by Complement Activation in a Rat Peritonitis Model

Fungal peritonitis is an important complication in peritoneal dialysis patients; either continuous or recurrent peritonitis may enhance peritoneal damage. Even when the peritoneal dialysis catheter is removed in patients with fungal peritonitis, peritoneal fibrosis can progress and evolve into encapsular peritoneal sclerosis. It is unclear why fungal infections are worse than bacterial in these respects. Zymosan is a cell wall component of yeast that strongly activates the complement system. In this study, we compared the effects of zymosan and bacterial LPS on peritoneal inflammation in a rat peritoneal injury model induced by mechanical scraping. Intraperitoneal administration of zymosan, but not LPS or vehicle, caused markedly enhanced peritonitis with massive infiltration of cells and deposition of complement activation products C3b and membrane attack complex on day 5. In rats administered zymosan and sacrificed on days 18 or 36, peritoneal inflammation persisted with accumulation of ED-1-positive cells, small deposits of C3b and membrane attack complex, exudation of fibrinogen, and capillary proliferation in subperitoneal tissues. When zymosan was administered daily for 5 days after peritoneal scrape, there was even greater peritoneal inflammation with peritoneal thickening, inflammatory cell accumulation, and complement deposition. Inhibition of systemic complement by pretreatment with cobra venom factor or local inhibition by i.p. administration of the recombinant complement regulator Crry-Ig reduced peritoneal inflammation in zymosan-treated rats. Our results show that yeast components augment inflammation in the injured peritoneum by causing complement activation within the peritoneal cavity. Local anticomplement therapy may therefore protect from peritoneal damage during fungal infection of the peritoneum.

The crystal structure of cobra venom factor, a cofactor for C3- and C5-convertase CVFBb

Cobra venom factor (CVF) is a functional analog of human complement component C3b, the active fragment of C3. Similar to C3b, in human and mammalian serum, CVF binds factor B, which is then cleaved by factor D, giving rise to the CVFBb complex that targets the same scissile bond in C3 as the authentic complement convertases C4bC2a and C3bBb. Unlike the latter, CVFBb is a stable complex and an efficient C5 convertase. We solved the crystal structure of CVF, isolated from Naja naja kouthia venom, at 2.6 A resolution. The CVF crystal structure, an intermediate between C3b and C3c, lacks the TED domain and has the CUB domain in an identical position to that seen in C3b. The similarly positioned CUB and slightly displaced C345c domains of CVF could play a vital role in the formation of C3 convertases by providing important primary binding sites for factor B.

Development of an in vivo gene mutation assay using the endogenous Pig-A gene: I. Flow cytometric detection of CD59-negative peripheral red blood cells and CD48-negative spleen T-cells from the rat

The product of the phosphatidylinositol glycan complementation group A gene (Pig-A) is involved in the synthesis of glycosylphosphatidylinositol (GPI) anchors that link various protein markers to the surface of several types of mammalian cells, including hematopoietic cells. Previous observations indicate that Pig-A mutation results in the lack of GPI synthesis and the absence of GPI-anchored proteins on the cell surface. As a first step in designing a rapid assay for measuring Pig-A mutation in the rat, we developed flow cytometry (FCM) strategies for detecting GPI-negative cells in rat peripheral blood and spleen. Anti-CD59 was used to detect GPI-anchored proteins on red blood cells (RBCs), and anti-CD48 was used to detect GPI-anchored proteins on spleen T-cells. The spontaneous frequency of CD59-negative RBCs in five male F344 rats ranged from 1 x 10(-6) to 27 x 10(-6). In contrast, treatment of five rats with three doses of 40 mg/kg N-ethyl-N-nitrosourea (ENU) increased the frequency of CD59-negative RBCs to 183 x 10(-6) to 249 x 10(-6) at 2 weeks and to 329 x 10(-6) to 413 x 10(-6) at 4 weeks after dosing. In the same 4-week posttreatment rats, the frequency of CD48-negative T-cells was 11 x 10(-6) to 16 x 10(-6) in control rats and 194 x 10(-6) to 473 x 10(-6) in ENU-treated rats. The frequencies of GPI-deficient cells were similar for RBCs and spleen T-cells. These results indicate that FCM detection of GPI-linked markers may form the basis for a rapid in vivo mutation assay. Although RBCs may be useful for a minimally invasive assay, T-cells are a promising tissue for both detecting GPI-deficient cells and confirming that Pig-A gene mutation is the cause of the phenotype.

Monoclonal antibodies to rat leukocyte surface antigens, MHC antigens, and immunoglobulins

The CD nomenclature used for human-leukocyte surface antigens is now being widely applied to naming their homologs in other species. This appendix catalogs those CD antigens that have been clearly defined in the rat. There are also many other antigens defined in the rat, but only those for which good biochemical data are available, such as amino acid sequences, are given here. The most commonly used antibodies are summarized.

Isolation and functional assay of the membrane complement inhibitors CD55 (DAF) and CD59 (MIRL)

The complement system is the primary effector of humoral immunity. Because of its enormous destructive capacity, mechanisms for confining the activity of the system to the desired target and elaborate safeguards for protecting self against complement-mediated injury have evolved. Human cells, particularly those found at sites of inflammation (e.g., hematopoietic and endothelial cells), express highly specialized membrane constituents that act independently or in concert with plasma regulatory proteins to inhibit the functional activity of complement. Decay-accelerating factor (DAF), or CD55, directly inhibits the formation and stability of the amplification C3 and C5 convertases of both the classical and the alternative pathways. Failure of a cell to regulate the amplification C3 and C5 convertases allows the generation of the potentially cytolytic membrane attack complex (MAC), or C5b-9 (consisting of the complement components C5b, C6, C7, C8, and C9). The primary cellular regulator of the MAC is the membrane inhibitor of reactive lysis (MIRL), or CD59, which restricts complement-mediated lysis by blocking assembly of the MAC (primarily at the stage of C9 binding and polymerization). This unit provides a basic protocol for isolating CD55 and CD59, along with two support protocols describing separate functional assays for CD59 and CD55.

A protein toxin from the sea anemone Phyllodiscus semoni targets the kidney and causes a severe renal injury with predominant glomerular endothelial damage

Envenomation by the sea anemone Phyllodiscus semoni causes fulminant dermatitis and, rarely, acute renal failure in humans. Here, we investigated whether the venom extracted from the nematocysts (PsTX-T) was nephrotoxic when administered intravenously in rats and whether PsTX-T induced activation of the complement system. Although small dose of PsTX-T induced acute tubular necrosis in rats resembling pathology seen in patients, kidneys displayed glomerular injury with glomerular endothelial damage, thrombus formation, mesangiolysis, and partial rupture of glomerular basement membrane, accompanied by severe tubular necrosis at 24 hours after administration of 0.03 mg of PsTX-T per animal, similar to the glomerular findings typical of severe hemolytic uremic syndrome. The early stage injury was accompanied by specific PsTX-T binding, massive complement C3b, and membrane attack complex deposition in glomeruli in the regions of injury and decreased glomerular expression of complement regulators. A pathogenic role for complement was confirmed by demonstrating that systemic complement inhibition reduced renal injury. The isolated nephrotoxic component, a 115-kd protein toxin (PsTX-115), was shown to cause identical renal pathology. The demonstration that PsTX-T and PsTX-115 were highly nephrotoxic acting via induction of complement activation suggests that inhibition of complement might be used to prevent acute renal damage following envenomation by P. semoni.

Suppression of complement regulatory proteins (CRPs) exacerbates experimental autoimmune anterior uveitis (EAAU)

This study was undertaken to explore the role of complement regulatory proteins (CRPs) in experimental autoimmune anterior uveitis (EAAU). We observed that the levels of CRPs, Crry and CD59, in the eyes of Lewis rats increased during EAAU and remained elevated when the disease resolved. The in vivo role of these CRPs in EAAU was explored using neutralizing mAbs, antisense oligodeoxynucleotides (AS-ODNs), and small interfering RNAs against rat Crry and CD59. Suppression of Crry in vivo at days 9, 14, or 19 by neutralizing mAb or AS-ODNs resulted in the early onset of disease, the exacerbation of intraocular inflammation, and delayed resolution. Suppression of CD59 was only effective when the Abs and ODNs were given before the onset of disease. The most profound effect on the disease was observed when a mixture of Crry and CD59 mAbs or AS-ODNs was administered. A similar effect was observed with a combination of Crry and CD59 small interfering RNA. There was no permanent histologic damage to ocular tissue after the inflammation cleared in these animals. Increased complement activation as determined by increased deposition of C3, C3 activation fragments, and membrane attack complex was observed in the eyes of Lewis rats when the function and/or expression of Crry and CD59 was suppressed. Thus, our results suggest that various ocular tissues up-regulate the expression of Crry and CD59 to avoid self-injury during autoimmune uveitis and that these CRPs play an active role in the resolution of EAAU by down-regulating complement activation in vivo.

Characterisation of the complement susceptibility of the rat aortic smooth muscle cell line A7r5

Complement (C) activation is thought to contribute to the initiation and progression of atherosclerosis. Proliferation of smooth muscle cells plays an important role in atherosclerotic plaque formation. Our aim was to investigate the suitability of the rat aortic smooth muscle cell line A7r5 as an in vitro model to study C-induced events in smooth muscle cells. A7r5 cells abundantly expressed membrane bound C-regulators (CReg) Crry and CD59 as assessed by flow-cytometry, but no DAF or MCP was detected. Using RT-PCR in addition to Crry and CD59, also mRNA for rat DAF but not for MCP was detected. Flow-cytometry of cells removed by EDTA instead of trypsin demonstrated that A7r5 did express cell surface DAF. Upon prolonged culturing under either logarithmic growing conditions or under conditions where cells were kept over-confluent, two different sub cell lines were obtained, one which had lost the expression of CD59, while the other showed increased expression of DAF and Crry. The change in expression of these CReg resulted in a change in C-susceptibility. Incubation of the A7r5 cells with human serum induced membrane attack complex dependent proliferation. Transfection with human CD59 efficiently protected the cells from C-mediated killing and C-induced cell proliferation. Our results show that A7r5 cells can be used as an in vitro model for C-induced events, but care has to be taken to use the cells at an early stage of passaging as they readily change their phenotype.

Spermatogenic cells distal to the blood-testis barrier in rats lack C3 convertase regulators and may be at risk of complement-mediated injury

On most tissues, multiple membrane complement regulators (CReg) protect self-cells from damage by complement. An exception is the brain, where the blood-brain barrier provides a protected environment within which cells survive with little or no protection from complement. The testis has a functionally similar structure, the blood-testis barrier (BTB). Here, we have investigated the expression of C3/C5 convertase CReg and C3 in the normal rat testis at different ages and different spermatogenetic stages, as well as in rats in which spermatogenesis and the BTB were impaired due to a developmental deficit. Immature testis, prior to BTB formation at puberty, displayed broad expression of the ubiquitous rodent CReg Crry on all elements and no expression of CD46 or CD55. Within days of BTB formation, CReg expression was dramatically altered; Crry was expressed only in the spermatogenetic cells external to the BTB in basal layers of adult seminal epithelium. Spermatogenic cells immediately distal to the BTB at first expressed no C3/C5 convertase regulators but later acquired expression of CD46 and CD55. Staining for C3 was widespread pre-puberty, but absent distal to the BTB in mature rats. In rats with defects in spermatogenesis and BTB integrity, expression patterns of CReg and C3 resembled those in pre-pubertal normals. The relative paucity of CReg and absence of C3 synthesis distal to the BTB suggest the presence of a complement-protected environment analogous to that described in the brain, and suggest also that cells enclosed by the BTB may be susceptible to complement damage when the barrier is breached.

Complement inhibitors targeted to the proximal tubule prevent injury in experimental nephrotic syndrome and demonstrate a key role for C5b-9

In glomerular diseases of diverse etiologies, dysfunction of the glomerular barrier to protein passage results in proteinuria, and proteinuria is considered an independent risk factor that plays a direct role in inflammation, interstitial fibrosis, and renal failure. The mechanism by which proteinuria leads to nephrotoxic injury is unclear, but a role for complement in mediating interstitial damage appears likely. We describe a strategy for Ag-specific targeting of complement inhibitors using a single chain Ab fragment and show that complement inhibitors targeted to the tubular epithelium protect against tubulointerstitial injury and renal dysfunction in a rat model of puromycin-induced nephrosis. The targeting of systemically administered complement inhibitors markedly enhanced their efficacy and obviated the need to systemically inhibit complement, thus reducing the risk of compromising host defense and immune homeostasis. Targeted inhibition of complement activation by Crry, and of membrane attack complex (MAC) formation by CD59 was equally therapeutic, demonstrating that the MAC plays a key role in proteinuria-induced tubulointerstitial injury. CD59 activity was dependent on its being targeted to the site of complement activation, and this is the first report of specific inhibition of the MAC in vivo after systemic administration of inhibitor. The data establish the MAC is a valid target for pharmaceutical intervention in proteinuric disorders and provide an approach to investigate the role of the MAC in complement-dependent disease under clinically relevant conditions.

Generation of a recombinant, membrane-targeted form of the complement regulator CD59: activity in vitro and in vivo

Inappropriate activation of complement contributes to pathology in diverse inflammatory diseases. Soluble recombinant forms of the natural cell membrane regulators of complement are effective in animal models and some human diseases. However, their use is limited for reasons related to cost, short half lives, and propensity to cause unwanted systemic effects. Some of these limitations may be overcome by use of bacterial expression systems, specific targeting moieties, and judicious choice of regulator. Here we describe the application of these strategies to the generation of a membrane-targeted form of CD59. A recombinant soluble form of rat CD59, comprising the first 71 residues of the mature protein and missing the membrane-anchoring signal, was expressed in bacteria, purified, and refolded in a fully active form. The protein was coupled through its carboxyl terminus to a short, synthetic address tag that confers membrane binding activity. Attachment of the membrane address tag markedly increased complement-inhibitory activity assessed in vitro in hemolysis assays. Intra-articular administration of the tagged agent markedly suppressed disease in a model of rheumatoid arthritis in Lewis rats. This novel type of agent, termed sCD59-APT542, offers for the first time the prospect of efficient and specific inhibition of membrane attack complex activity in vivo.

Characterization of the mouse analogues of CD59 using novel monoclonal antibodies: tissue distribution and functional comparison

CD59, the sole membrane regulator of the membrane attack complex of complement, is broadly and abundantly expressed in man and other mammals. In mouse, CD59 is encoded by two homologous genes. The expression patterns and functional roles of the proteins encoded by these genes, mCD59a and mCD59b, have not been well characterized. Here we describe the generation of monoclonal and polyclonal antibodies detecting specifically mCD59a and mCD59b. These reagents have been used to study function and to ascertain the cell and tissue distributions of mCD59a and mCD59b. mCD59a was broadly distributed on endothelia, erythrocytes, platelets, and on numerous other cell types in organs, a distribution pattern resembling that of CD59 in other species. In marked contrast, expression of mCD59b was restricted to germ cell elements in the testis and mature spermatozoa. Both mCD59a and CD59b inhibited human and rodent complement with similar efficiency. These findings demonstrate that the broadly distributed mCD59a is the key regulator of the terminal complement pathway in mice whereas CD59b, expressed only in testis and on sperm, probably plays other roles in vivo.

Decay-accelerating factor expression in the rat kidney is restricted to the apical surface of podocytes

BACKGROUND

Decay-accelerating factor (DAF) has inhibitory activity toward complement C3 and C5 convertases. DAF is present in human glomeruli and on cultured human glomerular visceral epithelial cells (GEC). We studied the distribution and function of rat DAF.

METHODS

Function-neutralizing antibodies (Abs) were raised against DAF. The distribution of DAF in vivo was determined by immunoelectron microscopy. Functional studies were performed in cultured GEC and following IV injection of anti-DAF Abs into rats.

RESULTS

DAF was present exclusively on the apical surfaces of GEC, and was not present on the basal surfaces of GEC, nor other glomerular or kidney cells. DAF was functionally active on cultured GEC, and served to limit complement activation in concert with CD59, an inhibitor of C5b-9 formation. Upon injection into normal rats, anti-DAF F(ab')2 Abs bound to GEC in vivo, yet there was no evidence for complement activation and animals did not develop abnormal albuminuria. Anti-megalin complement-activating IgG Abs were "planted" on GEC, which activated complement as evidenced by the presence of C3d on GEC. Attempts to inhibit DAF function with anti-DAF Abs did not affect the quantity of complement activation by these anti-megalin Abs, nor did it lead to development of abnormal albuminuria. In contrast, in the puromycin aminonucleoside model of GEC injury and proteinuria, anti-DAF Abs slowed the recovery from renal failure that occurs in this model.

CONCLUSION

In cultured rat GEC, DAF is an effective complement regulator. In vivo, DAF is present on GEC apical surfaces. Yet, it appears that DAF is not essential to prevent complement activation from occurring under normal circumstances and in those cases in which complement-activating Abs are present on the basal surfaces of GEC in vivo. However, in proteinuric conditions, DAF appears to be protective to GEC.

Rat T cells express neither CD55 nor CD59 and are dependent on Crry for protection from homologous complement

All human blood cells express decay-accelerating factor (DAF, CD55), CD59, and, with the exception of erythrocytes, membrane cofactor protein (MCP, CD46) to protect themselves from damage by the constant low-level activation of complement in serum. In rats and mice MCP is expressed only in testis, whereas DAF and CD59 are broadly distributed. Rats and mice also express a unique complement regulator, Crry. Previously we have shown that DAF was absent from at least 75% of rat T cells. To further investigate this surprising finding, we assessed the expression levels of DAF, CD59 and Crry on all blood cell types in the rat. We found that Crry was abundantly expressed on all blood cells. CD59 was expressed abundantly on erythrocytes and granulocytes but was absent from all T cellsand platelets and a minority of B cells and NK cells. Double staining and depletion studies showed that T cells in all rat strains tested were DAF-CD59-. Neutralization of Crry using a blocking monoclonal antibody rendered T cells susceptible to lysis by homologous complement, indicating that Crry was solely responsible for protecting DAF-CD59- T cells from complement damage in the rat.

Blockage of complement regulators in the conjunctiva and within the eye leads to massive inflammation and iritis

The open environment of the eye is continuously subject to an influx of foreign agents that can activate complement. Decay-accelerating factor (DAF), membrane cofactor protein (MCP) and CD59 are regulators that protect self-cells from autologous complement activation on their surfaces. They are expressed in the eye at unusually high levels but their physiological importance in this site is unstudied. In the rat, a structural analogue termed 5I2 antigen (5I2 Ag) has actions overlapping DAF and MCP. In this investigation, we injected F(ab')2 fragments of 5I2 mAb into the conjunctiva and aqueous humor, in the latter case with and without concomitant blockage of CD59. Massive neutrophilic infiltration of the stroma and iris resulted upon blocking 5I2 Ag activity. Frank necrosis of the iris occurred upon concomitant intraocular blockage of CD59. C3b was identified immunohistochemically, and minimal effects were seen in complement-depleted animals and in those treated with non-relevant antibody. The finding that blockage of 5I2 Ag function in periocular tissues and within the eye causes intense conjunctival inflammation and iritis demonstrates the importance of intrinsic complement regulators in protecting ocular tissues from spontaneous or bystander attack by autologous complement.

Interaction between host complement and mosquito-midgut-stage Plasmodium berghei

After ingestion by mosquitoes, gametocytes of malaria parasites become activated and form extracellular gametes that are no longer protected by the red blood cell membrane against immune effectors of host blood. We have studied the action of complement on Plasmodium developmental stages in the mosquito blood meal using the rodent malaria parasite Plasmodium berghei and rat complement as a model. We have shown that in the mosquito midgut, rat complement components necessary to initiate the alternative pathway (factor B, factor D, and C3) as well as C5 are present for several hours following ingestion of P. berghei-infected rat blood. In culture, 30 to 50% of mosquito midgut stages of P. berghei survived complement exposure during the first 3 h of development. Subsequently, parasites became increasingly sensitive to complement lysis. To investigate the mechanisms involved in their protection, we tested for C3 deposition on parasite surfaces and whether host CD59 (a potent inhibitor of the complement membrane attack complex present on red blood cells) was taken up by gametes while emerging from the host cell. Between 0.5 and 22 h, 90% of Pbs21-positive parasites were positive for C3. While rat red and white blood cells stained positive for CD59, Pbs21-positive parasites were negative for CD59. In addition, exposure of parasites to rat complement in the presence of anti-rat CD59 antibodies did not increase lysis. These data suggest that parasite or host molecules other than CD59 are responsible for the protection of malaria parasites against complement-mediated lysis. Ongoing research aims to identify these molecules.

Membrane complement regulatory proteins: insight from animal studies and relevance to human diseases

The complement system plays an important role in host defense. However, if not properly regulated, activated complement can also cause significant damage to host tissues. To prevent complement-mediated autologous tissue damage, host cells express a number of membrane-bound complement regulatory proteins. These include decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46) and CD59. Recent studies of membrane complement regulatory proteins from various animal species have revealed similarities as well as significant differences from the corresponding human proteins. In this review, we summarize recent advances in this area and contrast the structure, function and tissue distribution of membrane complement regulatory proteins in human and nonprimate mammalian species. We also discuss how the characterization of the animal proteins has provided important clues and might continue to show relevance to the pathogenesis and therapeutics of a number of human diseases.

GluR3 autoantibodies destroy neural cells in a complement-dependent manner modulated by complement regulatory proteins

GluR3 autoantibodies have been implicated in the development of Rasmussen's encephalitis, a rare neurodegenerative disease of humans characterized by epilepsy and degeneration of a single cerebral hemisphere. GluR3 autoantibodies are found in some Rasmussen's encephalitis patients, and GluR3 antibodies raised in rabbits destroy cultured cortical cells in a complement-dependent manner. In this study, the cellular targets of anti-GluR3 antisera-mediated cytotoxicity were examined in mixed primary neuronal-glial cultures of rat cortex. Unexpectedly, astrocytes were the principal target of the cytotoxic effects as assessed by immunohistochemistry and lactate dehydrogenase activity; neurons were destroyed to a lesser extent. Astrocyte vulnerability was rescued by transfection with complement regulatory proteins, and neuronal resistance was defeated by impairing complement regulatory protein function. Astrocyte death may occur in Rasmussen's encephalitis, and destruction of this cell type may play a critical role in the progression of this disorder. The present findings suggest complement regulatory protein expression may in part determine the nature and severity of Rasmussen's encephalitis and other complement-dependent nervous system diseases and thus underscore the need for a systematic investigation of the expression of all known complement regulatory proteins in healthy and diseased nervous system tissues.

Chronic low level complement activation within the eye is controlled by intraocular complement regulatory proteins

PURPOSE

To explore the role of the complement system and complement regulatory proteins in an immune-privileged organ, the eye.

METHODS

Eyes of normal Lewis rats were analyzed for the expression of complement regulatory proteins, membrane cofactor protein (MCP), decay-acceleration factor (DAF), membrane inhibitor of reactive lysis (MIRL, CD59), and cell surface regulator of complement (Crry), using immunohistochemistry, Western blot analysis, and reverse transcription-polymerase chain reaction (RT-PCR). Zymosan, a known activator of the alternative pathway of complement system was injected into the anterior chamber of the eye of Lewis rats. Animals were also injected intracamerally with 5 microl (25 microg) of neutralizing monoclonal antibody (mAb) against rat Crry (5I2) or CD59 (6D1) in an attempt to develop antibody induced anterior uveitis; control animals received 5 microl of sterile phosphate-buffered saline (PBS), OX-18 (25 microg), G-16-510E3 (25 microg), or MOPC-21 (25 microg). The role of complement system in antibody-induced uveitis was explored by intraperitoneal injection of 35 U cobra venom factor (CVF), 24 hours before antibody injection. Immunohistochemical staining and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with Western blot analysis were used to detect the presence of membrane attack complex (MAC) and C3 activation products, respectively, in normal and antibody-injected rat eyes.

RESULTS

Complement activation product MAC was present in the normal rat eye, and intraocular injection of zymosan induced severe anterior uveitis. The complement regulatory proteins, MCP, DAF, CD59, and Crry, were identified in the normal rat eye. Soluble forms of Crry and CD59 were also detected in normal rat aqueous humor. Severe anterior uveitis developed in Lewis rats injected with a neutralizing mAb against Crry, with increased formation of C3 split products. Systemic complement depletion by CVF prevented the induction of anterior uveitis by anti-Crry mAb. Intracameral injection of anti-rat CD59 (6D1), anti-rat MHC class I antigen (OX-18), anti-rat Ig (G-16-510E3), or MOPC-21 caused no inflammatory reaction.

CONCLUSIONS

The results suggest that the complement system is continuously active at a low level in the normal eye and is tightly regulated by intraocular complement regulatory proteins.

GluR3 autoantibodies destroy neural cells in a complement-dependent manner modulated by complement regulatory proteins

GluR3 autoantibodies have been implicated in the development of Rasmussen's encephalitis, a rare neurodegenerative disease of humans characterized by epilepsy and degeneration of a single cerebral hemisphere. GluR3 autoantibodies are found in some Rasmussen's encephalitis patients, and GluR3 antibodies raised in rabbits destroy cultured cortical cells in a complement-dependent manner. In this study, the cellular targets of anti-GluR3 antisera-mediated cytotoxicity were examined in mixed primary neuronal-glial cultures of rat cortex. Unexpectedly, astrocytes were the principal target of the cytotoxic effects as assessed by immunohistochemistry and lactate dehydrogenase activity; neurons were destroyed to a lesser extent. Astrocyte vulnerability was rescued by transfection with complement regulatory proteins, and neuronal resistance was defeated by impairing complement regulatory protein function. Astrocyte death may occur in Rasmussen's encephalitis, and destruction of this cell type may play a critical role in the progression of this disorder. The present findings suggest complement regulatory protein expression may in part determine the nature and severity of Rasmussen's encephalitis and other complement-dependent nervous system diseases and thus underscore the need for a systematic investigation of the expression of all known complement regulatory proteins in healthy and diseased nervous system tissues.

CD59 protects rat kidney from complement mediated injury in collaboration with crry

BACKGROUND

As previously reported, the membrane-bound complement regulator at the C3 level (Crry/p65) is important in maintaining normal integrity of the kidney in rats. However, the role of a complement regulator at the C8/9 level (CD59) is not clear, especially when activation of complement occurs at the C3 level. The aim of this work was to elucidate the in vivo role of CD59 under C3 activating conditions.

METHODS

Two monoclonal antibodies, 5I2 and 6D1, were used to suppress the function of Crry and CD59, respectively. In order to activate alternative the pathway of complement, the left kidney was perfused with 5I2 and/or 6D1 and was recirculated.

RESULTS

In the kidneys perfused with 5I2 alone, deposition of C3 and membrane attack complex (MAC) was observed in the peritubular capillaries, vasa recta, and tubular basement membranes. Cast formation, tubular dilation and degeneration, and cellular infiltration were observed at days 1 and 4, and they recovered by day 7. Further suppression of CD59 by 6D1 significantly enhanced the deposition of MAC and worsened the already exacerbated tubulointerstitial injury. These effects of 6D1 were dose dependent. Perfusion with 6D1 alone did not induce histologic damage or MAC deposition in the tubulointerstitium.

CONCLUSIONS

In rats, CD59 maintains normal integrity of the kidney in collaboration with Crry in rats against complement-mediated damage in vivo.

Identification of mutations in rat CD59 that increase the complement regulatory activity

Formation of the membrane attack complex (MAC) of complement on host cells is inhibited by the glycosylphosphatidylinositol- (GPI-) anchored glycoprotein CD59. Published data on the active site of human CD59 are confusing. To clarify these data, we set out to elucidate the active site of a nonprimate CD59 molecule by site-directed mutagenesis. We also undertook to investigate a region of potential species selectivity, and to this end rat CD59 was chosen for all mutations. Our investigations confirmed the proposal that the active site of CD59 is the major hydrophobic groove, with mutations Y36A, W40A, and L54A ablating complement inhibitory function of CD59. Other mutations reducing the function of rat CD59 were I56E, D24A, and D24R. Importantly, mutations at one residue increased the function of rat CD59. The K48E mutation significantly increased function against human rat or rabbit serum, whereas the K48A mutation increased function against human serum alone. A similar mutation in human CD59 (N48E) had no effect on activity against human or rat serum but completely abolished all activity against rabbit serum. These findings suggest that the alpha-helix of human CD59, adjacent to the hydrophobic groove, influences the interaction between human CD59 and rabbit C8, C9, or both.

High-resolution FRET microscopy of cholera toxin B-subunit and GPI-anchored proteins in cell plasma membranes

"Lipid rafts" enriched in glycosphingolipids (GSL), GPI-anchored proteins, and cholesterol have been proposed as functional microdomains in cell membranes. However, evidence supporting their existence has been indirect and controversial. In the past year, two studies used fluorescence resonance energy transfer (FRET) microscopy to probe for the presence of lipid rafts; rafts here would be defined as membrane domains containing clustered GPI-anchored proteins at the cell surface. The results of these studies, each based on a single protein, gave conflicting views of rafts. To address the source of this discrepancy, we have now used FRET to study three different GPI-anchored proteins and a GSL endogenous to several different cell types. FRET was detected between molecules of the GSL GM1 labeled with cholera toxin B-subunit and between antibody-labeled GPI-anchored proteins, showing these raft markers are in submicrometer proximity in the plasma membrane. However, in most cases FRET correlated with the surface density of the lipid raft marker, a result inconsistent with significant clustering in microdomains. We conclude that in the plasma membrane, lipid rafts either exist only as transiently stabilized structures or, if stable, comprise at most a minor fraction of the cell surface.

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.

Comparison of the suppressive effects of soluble CR1 and C5a receptor antagonist in acute arthritis induced in rats by blocking of CD59

We investigated the effects of suppression of complement activation at C3 level and inhibition of C5a on acute synovitis in rats. Acute synovitis was induced in Wistar rats by intra-articular (i.a.) injection into one knee of 0.3 mg of MoAb 6D1 (anti-rat CD59 antibody). In the treatment groups, soluble CR1 (sCR1) or C5a receptor (C5aR) antagonist was administered intra-articularly or intravenously and effects on the course of the acute synovitis were monitored. Synovitis induced by 6D1 was characterized by joint swelling, thickening of synovial tissue, cellular infiltration and deposition of membrane attack complex (MAC) on the synovial surface. Neither inflammatory change nor MAC deposition was found in rats which received an i.a. injection of sCR1 to suppress complement activity in the joint. Intra-articular injection of sCR1 did not reduce plasma complement activity. Intravenous administration of sCR1 suppressed plasma complement activity but had no effect on the course of the arthritis and synovitis with MAC deposition was observed. Neither i.a. nor i.v. injection of C5aR antagonist had any suppressive effects on inflammatory change or MAC deposition in synovium. The data show that inflammatory change induced by 6D1 was mediated by local complement activation and was not accompanied by systemic complement activation. C5a generation was not responsible for the observed inflammation, suggesting that other complement activation products, possibly MAC, mediate the inflammatory change observed in this model of acute synovitis in rats.

Production and functional analysis of rat CD59 and chimeric CD59-Crry as active soluble proteins in Pichia pastoris

Crry (CR1-related gene/protein) is a rodent complement regulator that inhibits C3 convertases. CD59 is a conserved protein inhibitor active towards C8 and C9. We have previously produced rat Crry as a recombinant soluble (rs) protein in Pichia pastoris. In this study we produced functionally active rat rsCD59 and a chimeric rsCD59-Crry protein in P. pastoris. The GPI anchor addition site of rat CD59 (Asn-79) was replaced either by a stop codon to produce rsCD59, or with the sequence of the first five short consensus repeats of Crry to produce rsCD59-Crry. Proteins were generated by fermentation and purified by affinity chromatography on an anti-CD59 column. In a standard classical pathway haemolysis assay, all three rs proteins had inhibitory activity, with 50% inhibition at 0.5 microM (rsCrry and rsCD59-Crry) and 4.4 microM (rsCD59). In an assay examining inhibition of C5b-9, in which C5b-7 was first formed, followed by purified C8 and C9, rsCD59 and rsCD59-Crry were active with 50% inhibition at 0.8 microM (rsCD59-Crry) and 1.3 microM (rsCD59). The degree of inhibition was independent of whether the C8 and C9 were of rat or human origin. Therefore, we have produced rsCD59 and rsCD59-Crry in P. pastoris. The rsCD59 retains its inhibitory activity towards C5b-9, while rsCD59-Crry appears to have the combined activities of Crry and CD59. In a haemolytic assay, the inclusion of CD59 to Crry is of no additional benefit to Crry, which may illustrate the overall importance of the C3 convertase step. Yet, inclusion of Crry to CD59 increases the potency of CD59 towards C5b-9.

Development of Adenovirus Vectors Encoding Rat Complement Regulators for Use in Therapy in Rodent Models of Inflammatory Diseases

C activation has been implicated in the pathogenesis of numerous inflammatory human diseases and disease models. A therapy based on C inhibition might therefore be of benefit to reduce inflammation and ameliorate disease. C inhibition in vivo can be accomplished by the delivery of soluble recombinant C regulators either systemically or directly to a target site, but effects are transitory. We have developed a strategy for the efficient delivery of the membrane-bound rat C inhibitors, CD59, Crry, and decay-accelerating factor (DAF), using replication-deficient adenovirus vectors with the intention of treating rat models of disease in which C is implicated. The adenovirus recombinants(RAd), RAdCD59, RAdCrry, and RAdDAF, respectively, have been tested for expression and function of the transgene in vitro. Infection of human fetal foreskin fibroblasts resulted in high levels of expression of each of the rat inhibitors. The constructs were also tested for inhibition of rat C-mediated cell lysis and C3b deposition. In a cell lysis assay, each inhibited to varying degrees of efficiency in the order RAdCD59 = RAdDAF > RAdCrry. In a C3b deposition assay, RAdDAF caused a greater reduction in C3b deposition than RAdCrry and RAdCD59 was ineffective. These agents, individually or in combination, provide the tools for testing the effects of prolonged inhibition of C at a target site on the progress of experimental models of disease.

Role of complement regulatory membrane proteins in ischaemia-reperfusion injury of rat gastric mucosa

BACKGROUND

The role of complement in ischaemia-reperfusion injury has not been well investigated. 5I2 is a monoclonal antibody (mAb) directed against a rat membrane inhibitor of the C3 convertase step, which is the rat counterpart of mouse Crry/p65. 6D1 is a mAb against rat CD59 which inhibits the formation of membrane attack complexes.

METHODS

We visualized the tissue distribution of these membrane inhibitors in rat gastrointestinal tract by immunohistochemical staining with the appropriate mAb. Then, we tested the hypothesis that complement regulatory proteins protect rat gastric mucosa against ischaemia-reperfusion stress by using these mAbs. Gastric mucosal integrity was continuously monitored by measuring the blood-to-lumen clearance of [51Cr]-labelled ethylenediaminetetraacetic acid (EDTA) under control conditions, during ischaemia and after reperfusion.

RESULTS

Rat 6D1 and 5I2 antigens were both widely distributed and predominantly expressed on smooth muscle and endothelial cells in gastrointestinal tracts. Blockade of complement regulatory proteins with 5I2 and 6D1 mAbs resulted in a significant increase in [51Cr]-EDTA clearance after reperfusion.

CONCLUSIONS

These findings support the hypothesis that endogenous complement regulatory proteins may act as important protective factors against ischaemia-reperfusion stress in rat gastric mucosa.

Tissue distribution of the rat analogue of decay-accelerating factor

In humans, decay-accelerating factor (DAF) is a widely distributed, cell-bound inhibitor of the complement activation enzymes and plays a key role in regulating complement activation, preventing the generation of anaphylotoxins and opsonins, and protecting against complement-mediated lysis. Rodent analogues of DAF have recently been identified, providing a new avenue for the analysis of function. Rat DAF was cloned in our laboratory. Here we describe the generation of monoclonal antibodies (mAbs) against rat DAF, using transfected cells as immunogen, and their use in the analysis of the distribution of DAF in the rat by flow cytometry, Western blot analysis and immunohistochemistry. One of the mAbs was found to block the complement inhibitory function of rat DAF, offering the prospect of neutralization of DAF function in vivo. The antibodies have also been used for purification of DAF from rat erythrocytes by affinity chromatography. Rat DAF purified in this manner was similar in molecular mass to human DAF. The purified protein incorporated into lipid membranes, confirming the presence of a glycolipid anchor, and incorporated protein strongly inhibited the rat C3 convertase. Rat DAF was strongly expressed on endothelia throughout the animal and was also present in most tissues and organs. DAF expression was weak or absent in the brain and on circulating and spleen-resident T cells. Strong DAF expression observed in the kidney was restricted to the glomerulus and Bowman's capsule. DAF expression in the testis was found only in association with the later stages of spermatogenesis.

Inhibition of a Membrane Complement Regulatory Protein by a Monoclonal Antibody Induces Acute Lethal Shock in Rats Primed with Lipopolysaccharide

Rats pretreated with traces of LPS developed acute fatal shock syndrome after i.v. administration of a mAb that inhibits the function of a membrane complement regulatory molecule. Such a shock was not observed after the administration of large amounts of LPS instead of the mAb following LPS pretreatment. The lethal response did not occur in rats depleted of either leukocytes or complement, and a C5a receptor antagonist was found to inhibit the reaction. Furthermore, LPS-treated rats did not suffer fatal shock following the injection of cobra venom factor, which activates complement in the fluid phase so extensively as to exhaust complement capacity. Therefore, complement activation on cell membranes is a requirement for this type of acute reaction.

Protection of human breast cancer cells from complement-mediated lysis by expression of heterologous CD59

CD59, decay accelerating factor (DAF) and membrane cofactor protein (MCP) are widely expressed cell surface glycoproteins that protect host cells from the effects of homologous complement attack. Complement inhibitory activity of these proteins is species-selective. We show that the human breast cancer cell line MCF7 is relatively resistant to lysis by human complement, but is effectively lysed by rat or mouse complement. CD59, DAF and MCP were all shown to be expressed by MCF7. The species-selective nature of CD59 activity was used to demonstrate directly the effectiveness of CD59 at protecting cancer cells from complement-mediated lysis. cDNAs encoding rat and mouse CD59 were separately transfected into MCF7 cells, and cell populations expressing high levels of the rodent CD59 were isolated by cell sorting. Data show that rat and mouse CD59 were highly effective at protecting transfected MCF7 cells from lysis by rat and mouse complement, respectively. Data further reveal that rat CD59 is not effective against mouse complement, whereas mouse CD59 is effective against both mouse and rat complement. These studies establish a model system for relevant in vivo studies aimed at determining the effect of complement regulation on tumourigenesis, and show that for effective immunotherapy using complement-activating anti-tumour antibodies, the neutralization of CD59 and/or other complement inhibitory molecules will probably be required.

Molecular Cloning and Functional Characterization of the Rat Analogue of Human Decay-Accelerating Factor (CD55)

We report here the cloning of cDNAs encoding two forms of the rat analogue of human decay-accelerating factor (DAF; CD55). Screening of a rat kidney cDNA library using a mouse DAF probe identified a partial cDNA encoding the 3′ end of rat DAF. The 5′ end of the cDNA was cloned using the rapid amplification of cDNA ends (RACE) technique. A second form of rat DAF was identified using 3′RACE. Cloning and sequencing of full length cDNAs for both forms showed that they were identical up to nucleotide 1143 except for a 51-bp insert in the ST-rich region of the second form. After nucleotide 1143, the two sequences diverged; the cDNA cloned from the library encoded a unique 112-amino acid “tail,” whereas the second form, identified by 3′RACE, encoded an 18-amino acid hydrophobic stretch, which was predicted to be a glycosylphosphatidylinositol (GPI) anchor addition signal. Expression in the NIH-3T3 mouse fibroblast cell line confirmed that the short tail did encode a GPI-addition signal, whereas the longer tail caused the protein to be secreted. Northern blot analysis identified two distinct transcripts for the GPI form, as well as a variability in expression levels of the different transcripts in the panel of tissues screened. Southern blot analysis showed that both the GPI and secreted forms of rat DAF were expressed in a wide range of tissues. The GPI-linked form of rat DAF stably expressed in a murine fibroblast cell line reduced C3 deposition and conferred protection from lysis by rat serum.

Characterization in vitro and in vivo of the pig analogue of human CD59 using new monoclonal antibodies

CD59 is the sole characterized regulator of the complement membrane attack complex in humans. It is very widely and abundantly distributed, being present on all circulating cells, endothelia and epithelia, and in most tissues. CD59 analogues in rodents are distributed similarly. Interest in complement regulation in the pig has developed out of the current enthusiasm to exploit this species as a donor in xenotransplantation of organs to humans. We have recently isolated and cloned the pig analogue of human CD59. We here report the development and characterization of monoclonal antibodies against pig CD59. We have used these antibodies to develop efficient methods for the purification of pig CD59 to homogeneity from erythrocyte membranes and have obtained new information on the structure and function of the purified protein. The antibodies were found to function well in immunohistochemistry and have been used to perform a comprehensive survey of the expression and distribution of pig CD59 on cells and in organs of normal pigs. Pig CD59, like human CD59, is broadly expressed but there are some striking differences in tissue distribution, notably the apparent lack of pig CD59 on circulating platelets and on a subset of leucocytes in blood and lymphoid organs. The reported findings have important implications for the current approaches to avoiding complement-mediated hyperacute rejection in pig-to-human xenografts.

Molecular Cloning and Functional Characterization of the Pig Analogue of CD59: Relevance to Xenotransplantation

In this work, we report the cloning of the cDNA for the porcine analogue of human CD59. Degenerate primers, derived from the N-terminal sequence of pig erythrocyte CD59, were used to obtain the corresponding cDNA sequence. From this sequence, gene-specific primers were designed and used to amplify the 3′ and 5′ ends of the cDNA using the rapid amplification of cDNA ends (RACE) method. The complete 768-bp cDNA so obtained consisted of a 84-bp 5′ untranslated region, a 26-amino-acid NH2-signal peptide, a 98-amino-acid coding region, including putative N-glycosylation sites and a glycosylphosphatidylinositol-anchoring signal, and a 312-bp 3′ untranslated region. The mature protein sequence was 48% identical to human CD59 at the amino acid level. Northern blot analysis revealed several distinct CD59 transcripts, and a variability in expression levels of the different transcripts in the panel of tissues screened. Stable expression of pig CD59 in a CD59-negative human cell line conferred protection against lysis by complement from pig and several other species. Separate expression of pig and human CD59 at similar levels in the same cell line allowed a direct functional comparison between these two analogues. Pig CD59 and human CD59 showed similar activity in inhibiting lysis by complement from all species tested; in particular, expressed pig CD59 efficiently inhibited lysis by human complement. The relevance of these data to current work in the engineering of pig organs for xenotransplantation is discussed.

Mapping the regions of the complement inhibitor CD59 responsible for its species selective activity

CD59 is a widely distributed membrane-bound glycoprotein that inhibits the formation of the cytolytic membrane attack complex (MAC) of complement on host cells. CD59 from different species varies in its capacity to inhibit heterologous complement, and this species selective function of CD59 contributes to the phenomenon of homologous restriction. Here, we demonstrate that human CD59 is not an effective inhibitor of rat complement, although rat CD59 inhibits rat and human complement equally well. By constructing human-rat CD59 chimeric proteins, we have mapped the residues important in conferring human CD59 species selectivity to two regions; 40-47 and 47-66 in the primary structure. Analysis of a model of the molecular surface of human CD59 revealed that residues 40-66 mapped to a region in the three-dimensional structure that surrounds residues previously identified as important for CD59 function.

Membrane attack complex of complement and 20 kDa homologous restriction factor (CD59) in myocardial infarction

In order to investigate the mechanism of deposition of the complement membrane attack complex (MAC) in cardiomyocytes in areas of human myocardial infarction, the 20 kDA homologous restriction factor of complement (HRF20; CD59) and complement components (Clq. C3d and MAC) were analysed immunohistochemically using specific antibodies. Myocardial tissues obtained at autopsy from nine patients who died of acute myocardial infarction were fixed in acetone and embedded in paraffin. The ages of the infarcts ranged from about 3.5 h to 12 days. In cases of myocardial infarction of 20 h or less, MAC deposition was shown in the infarcted cardiomyocytes without loss of HRF20. Where the duration was 4 days or more, the cardiomyocytes with MAC deposition in the infarcted areas also showed complete loss of HRF20. Outside the infarcts, HRF20 in the cardiomyocytes was well preserved without MAC deposition. The present study suggests that the initial MAC deposition in dead cardiomyocytes can occur as a result of degradation of plasma-membrane by a mechanism independent of complement-mediated injury to the membrane. Loss of HRF20 from dead cardiomyocytes may not be the initial cause of MAC deposition, but may accelerate the deposition process of MAC in later stages of infarction.

Expression of rat CD59: functional analysis confirms lack of species selectivity and reveals that glycosylation is not required for function

This study reports the expression and functional characterization of the rat analogue of the human complement regulatory molecule CD59. We here describe the expression in chinese hamster ovary (CHO) cells of rat CD59 and a modified rat CD59 in which an N-glycosylation site at Asn-16 has been deleted by point mutation. The complement-inhibiting capacity of these two forms of rat CD59 has been analysed and compared. Expressed rat CD59 efficiently inhibited complement lysis of CHO cells when rat serum was used as a source of complement and also inhibited lysis by complement from all other species tested, confirming that rat CD59 displayed little or no species restriction of activity. Blocking of expressed rat CD59 with a monoclonal antibody abrogated the inhibition of lysis for all sources of complement, confirming that the expressed molecule was responsible for the protection. The glycosylation mutant had a much reduced molecular weight on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) (12,000 MW as compared with 20,000-28,000 MW for unmutated), confirming that it was unglycosylated. However, the glycosylation mutant had complement-inhibitory activity which was at least as potent as that of the unmutated molecule, demonstrating that the large, N-linked carbohydrate moiety was not required for function.

The effects of functional suppression of a membrane-bound complement regulatory protein, CD59, in the synovial tissue in rats

OBJECTIVE

To investigate the roles of CD59 in the synovial tissue by functional suppression of CD59.

METHODS

Rats treated with cobra venom factor to deplete complement or untreated rats were injected intraarticularly with 0.3 mg of the F(ab')2 fraction of a monoclonal antibody, 6D1, that inhibits the function of rat CD59. The circumference of knee joints was measured, and histologic changes in the synovium were studied.

RESULTS

Joint swelling, thickening of the synovial tissues, infiltration of inflammatory cells into the synovium, and deposition of membrane attack complex (MAC) on the synovial surface were observed after intraarticular injection of 6D1. The inflammatory reaction reached its peak at 24 hours after injection, and finally subsided to normal within 3 days. It was suggested that functional suppression of CD59 in the synovium induced MAC formation followed by synovitis. Serum complement depletion did not completely suppress this reaction. This indicates that complement existing in the joint space is important for the formation of MAC on the synovial surface and for induction of synovitis.

CONCLUSION

The membrane-bound complement regulatory protein, CD59, plays a key role in the protection of joints against MAC-mediated synovial injury and in maintaining the normal integrity of the joint.

CD59 homologue regulates complement-dependent cytolysis of rat Schwann cells

Antibody (Ab) sensitized sciatic nerve Schwann cells (SchC) of 2-day-old rats (SchC/2d) were significantly more susceptible to cytolysis by both heterologous, guinea pig (GP), and homologous rat serum complement (40 +/- 3.8% and 21.2 +/- 3.1%, respectively) than SchC of 6-day-old rats (SchC/6d) (7.9 +/- 5.9% and 2.6 +/- 3.1%, respectively). To determine if resistance to complement (C)-mediated cytolysis correlated with expression of membrane proteins which regulate C activation, we used Western blot and FACS analysis. Binding of specific polyclonal Ab demonstrated similar concentrations of Crry, a regulator of C3 convertase formation, on plasma membranes of SchC 2d and 6d. During C activation, both C3b deposition and iC3b formation were greater on SchC/6d than on SchC/2d and the C3b deposition did not correlate with enhanced cytolysis. In contrast, 2.1-fold more rat CD59, a regulator of C8 and C9 incorporation into C5b-9, detected with Western blot on SchC/6d compared with SchC/2d was confirmed by FACS. Further, both rat and GP C8/C9 lysed SchC/2d expressing human C5b-7 (20.1 +/- 3.7 and 21.6 +/- 4.7%, respectively), while only GP C8/C9 caused cytolysis of 10.7 +/- 4.3% SchC/6d expressing hu C5b-7 and rat C8/C9 did not (0.5 +/- 0.5%). Preincubation of SchC/6d with an F(ab)2 fragment of an mAb to rCD59 with blocking capacity, increased cytolysis mediated by rat serum C more than 6-fold to 16.7 +/- 3.0% but only 1.7-fold (maximum cytolysis 37.4 +/- 11.2%) in SchC/2d. Our data suggest that expression of rat CD59 on SchC increased almost two-fold between postnatal days 2 and 6, and this increased expression on more terminally differentiated SchC is a significant factor in regulating terminal complement complex formation and limiting cytolysis of rat SchC by homologous serum complement.

Transfected CD59 protects mesangial cells from injury induced by antibody and complement

CD59 is a complement regulatory protein on the glomerular cells that inhibits C5b-9 assembly and insertion. We employed an overexpression strategy to determine the functional significance of CD59 in mesangial cells. We made a CD59 expression vector tagged with FLAG utilizing site-directed mutagenesis and PCR, which allows transfected CD59 to be distinguished from the constitutively expressed protein. In stable clones, overexpressed CD59 was clearly detected immunocytochemically both by anti-FLAG and anti-CD59 antibody in a granular pattern. The overexpression of CD59 was also confirmed by Western blotting. To determine if overexpression of CD59 by mesangial cells protected these cells from C5b-9 attack, we performed complement-mediated cell lysis assays. CD59-transfected mesangial cells demonstrated marked resistance to complement-mediated cell lysis which was reversed in the presence of antibody to CD59. We also investigated the role of CD59 in protecting cells from the effects of membrane insertion of sublytic quantities of C5b-9. Overexpressed CD59 suppressed production of superoxide, one of the inflammatory mediators induced by sublytic C5b-9 attack. These results demonstrate directly that transfected CD59 functions as a potent protector of mesangial cells against both lytic and sublytic attack by C5b-9. CD59 may be an important regulator of complement-mediated disease in the glomerular mesangium.