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PubMed2004

Human CD59 is a receptor for the cholesterol-dependent cytolysin intermedilysin.

Cholesterol is believed to serve as the common receptor for the cholesterol-dependent cytolysins (CDCs). One member of this toxin family, Streptococcus intermedius intermedilysin (ILY), exhibits a narrow spectrum of cellular specificity that is seemingly inconsistent with this premise. We show here that ILY, via its domain 4 structure, binds to the glycosyl-phosphatidylinositol-linked membrane protein human CD59 (huCD59). CD59 is an inhibitor of the membrane attack complex of human complement. ILY specifically binds to huCD59 via residues that are the binding site for the C8alpha and C9 complement proteins. These studies provide a new model for the mechanism of cellular recognition by a CDC.

Animals↗
PubMed2000

Fresh porcine cardiac valves are not rejected in primates.

OBJECTIVE: Transplanted porcine hearts are hyperacutely rejected by human immunoglobulin M antibodies against a porcine vascular endothelial molecule, galactose alpha-1,3-galactose, with ensuing human complement activation and membrane attack complex deposition. It is unclear, however, whether porcine valve endothelium triggers a similar immune response. We sought to investigate whether fresh porcine valves implanted into primates are rejected. METHODS: Wild-type porcine hearts before (n = 6) and after (n = 3) heterotopic transplantation into baboons underwent sectioning and were examined by hematoxylin and eosin staining and immunohistochemistry for galactose alpha-1,3-galactose, primate immunoglobulin M, and membrane attack complex. RESULTS: Examination of untransplanted porcine hearts showed that although cardiac microvascular endothelium strongly expressed the galactose alpha-1, 3-galactose antigen, galactose alpha-1,3-galactose was not detected on the endothelium of porcine aortic and pulmonary valves. Porcine hearts transplanted into baboon recipients were hyperacutely rejected 60 to 80 minutes after implantation. Despite dramatic tissue damage associated with extensive immunoglobulin M and membrane attack complex binding on the microvascular endothelium, the aortic and pulmonary valves were entirely spared. Valves remained morphologically intact at explant and showed no signs of immunoglobulin M- and membrane attack complex-mediated damage. CONCLUSIONS: The absence of galactose alpha-1,3-galactose expression may protect unfixed porcine valves from xenograft rejection in primates. Further investigation of viable porcine valves appears warranted.

Animals↗
PubMed1993

Meningococcal disease in patients with late complement component deficiency: studies in the U.S.S.R.

The purpose of this study was to examine the occurrence of late complement component deficiency (LCCD) states in the USSR. Thirty deficient individuals were detected: 27 with C8 beta and 3 with C7 deficiency. Among individuals with a first episode of meningococcal infection, about 1% had LCCD, whereas among patients with recurrent bacterial meningitis the prevalence of LCCD rose to approximately 50%. This corresponds to a prevalence for LCCD of approximately 12 per 100,000 in the general population. The individuals with LCCD identified in this study experienced about 77 episodes of meningococcal disease and acute bacterial meningitis. Mathematical analysis of the morbidity from meningococcal disease in individuals with LCCD demonstrated that the probability of disease did not change with the age of the patient and was not affected by prior episodes of infection. This finding suggest that in contrast to the situation in the general population, prior infection fails to protect the deficient individual from recurrent disease. In comparison to complement-sufficient persons, the course of disease in individuals with LCCD is less severe, as shown by a reduction in the number of episodes of endotoxic shock and mortality as well as their more rapid recovery. These findings suggest that exuberant complement activation and concomitant formation of membrane attack complexes during meningococcal infection in complement-sufficient patients plays an important role in the activation and injury of peripheral blood cells and endothelial cells during endotoxic shock.

Adolescent↗
PubMed2002

Myopathy with antibodies to the signal recognition particle: clinical and pathological features.

OBJECTIVES: To study myopathies with serum antibodies to the signal recognition particle (SRP), an unusual, myositis specific antibody associated syndrome that has not been well characterised pathologically. METHODS: Clinical, laboratory, and myopathological features were evaluated in seven consecutive patients with a myopathy and serum anti-SRP antibodies, identified over three years. The anti-SRP myopathy was compared with myopathology in other types of inflammatory and immune myopathies. RESULTS: The patients with anti-SRP antibodies developed weakness at ages ranging from 32 to 70 years. Onset was seasonal (August to January). Weakness became severe and disability developed rapidly over a period of months. Muscle pain and fatigue were present in some patients. No patient had a dermatomyositis-like rash. Serum creatine kinase was very high (3000 to 25 000 IU/l). Muscle biopsies showed an active myopathy, including muscle fibre necrosis and regeneration. There was prominent endomysial fibrosis, but little or no inflammation. Endomysial capillaries were enlarged, reduced in number, and associated with deposits of the terminal components of complement (C5b-9, membrane attack complex). Strength improved in several patients after corticosteroid treatment. CONCLUSIONS: Myopathies associated with anti-SRP antibodies may produce severe and rapidly progressive weakness and disability. Muscle biopsies show active myopathy with pathological changes in endomysial capillaries but little inflammation. Corticosteroid treatment early in the course of the illness is often followed by improvement in strength. In patients with rapidly progressive myopathies and a high serum creatine kinase but little inflammation on muscle biopsy, measurement of anti-SRP antibodies and pathological examination of muscle, including evaluation of endomysial capillaries, may provide useful information on diagnosis and treatment.

Adult↗
PubMed1999

Selective blockade of membrane attack complex formation during simulated extracorporeal circulation inhibits platelet but not leukocyte activation.

OBJECTIVE: Complement activation is induced by cardiopulmonary bypass, and previous work found that late complement components (C5a, C5b-9) contribute to neutrophil and platelet activation during bypass. In the present study, we blocked C5b-9 formation during extracorporeal recirculation of whole blood to assess whether the membrane attack complex was responsible for both platelet and leukocyte activation. METHODS: In a simulated extracorporeal model that activates complement (C3a and sC5b-9), platelets (CD62P expression, leukocyte-platelet conjugate formation), and leukocytes (increased CD11b expression and neutrophil elastase), we examined an anti-human C8 monoclonal antibody that inhibits C5b-9 generation for its effects on cellular activation. RESULTS: Anti-C8 significantly inhibited sC5b-9 formation but did not block C3a generation. Anti-C8 also significantly inhibited the increase in platelet CD62P and monocyte-platelet conjugate formation seen with control circulation. Moreover, compared with control circulation, in which the number of circulating platelets fell by 45%, addition of anti-C8 completely preserved platelet counts. In contrast to blockade of both C5a and sC5b-9 during simulated extracorporeal circulation, neutrophil activation was not inhibited by anti-C8. However, circulating neutrophil and monocyte counts were preserved by addition of anti-C8 to the extracorporeal circuit. CONCLUSIONS: The membrane attack complex, C5b-9, is the major complement determinant of platelet activation during extracorporeal circulation, whereas C5b-9 blockade has little effect on neutrophil activation. These data also suggest a role for platelet activation or C5b-9 (or both) in the loss of monocytes and neutrophils to the extracorporeal circuit.

Antibodies, Monoclonal↗
PubMed1986

Complement component C9 in Graves' disease.

C9, the terminal component of complement, is the key part of the membrane attack complex formed as a result of complement activation; it has also been reported to be an acute phase protein. Its potential role in Graves' disease has been studied by measuring plasma C9 concentrations using an automated two-site immunoradiometric assay employing monoclonal antibodies, whose binding to thyroid tissue has also been investigated. The plasma C9 concentration in patients with hyperthyroid Graves' disease (86.3 +/- 21.6 mg/l, mean +/- SD; n = 49) was significantly increased (P less than 0.001) compared with normal subjects (60.4 +/- 13.4 mg/l; n = 48). In contrast, the plasma concentration of C-reactive protein, a marker of the acute phase response, was not significantly different between the two groups. The plasma C9 concentration in patients with hyperthyroid Graves' disease decreased significantly (P less than 0.01) after treatment with antithyroid drugs (carbimazole or methimazole; n = 14), but not after radioactive iodine (131I) treatment (n = 18). Immunohistochemical staining demonstrated that monoclonal antibody to C9 bound to the basement membranes of thyroid follicular cells of Graves' thyroid tissue but not to normal thyroid tissue. Radiolabelled monoclonal antibody to C9 bound to membrane fragments prepared from thyroid glands from two patients with Graves' disease. We conclude that C9, and by implication the membrane attack complex, may be involved in the pathogenesis of Graves' disease.

Adult↗
PubMed1991

Measurement of SC5b-9 in urine in patients with the nephrotic syndrome.

In passive or active Heymann nephritis (HN) in the rat, the immune complexes that form in the glomerular subepithelial space result in complement activation and the urinary (U) excretion of S protein-membrane attack complex (SC5b-9, MAC). Because of the similarities between HN in rats and membranous nephropathy (MN) in humans, it has been suggested that measurement of SC5b-9 in urine (UMAC) could be useful in assessing the immunologic activity of MN in patients. The present study was undertaken in normal individuals and in patients with nephrotic syndrome to determine: 1) the conditions of urine collection and preservation needed for accurate measurement of UMAC for clinical purposes; and 2) whether UMAC levels are a sensitive and/or specific test for MN. In studies conducted on urine specimens from patients with increased UMAC levels, we found that UMAC in freshly voided urine was stable for at least three hours at 37 degrees C, with or without the addition of the enzyme inhibitors that were used to stabilize UMAC levels in the studies of HN in the rat. Urine pH, leukocytes and erythrocytes, over the ranges usually encountered, did not influence UMAC levels. However, freezing urine at -70 degrees C artifactually raised UMAC levels (1500 +/- 550 to 1800 +/- 580 SE ng/ml, P less than 0.001 by paired t-test). Normal urine contained low UMAC levels: 80 +/- 3 ng/mg urinary creatinine (UCr). By contrast, patients with glomerulopathies tended to have elevated UMAC levels: 18 of 38 patients had levels that ranged from 200 to 20,000 ng/mg UCr.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2005

Mechanisms of immune-deposit formation and the mediation of immune renal injury.

The passive trapping of preformed immune complexes is responsible for some forms of glomerulonephritis that are associated with mesangial or subendothelial deposits. The biochemical characteristics of circulating antigens play important roles in determining the biologic activity of immune complexes in these cases. Examples of circulating immune complex diseases include the classic acute and chronic serum sickness models in rabbits, and human lupus nephritis. Immune deposits also form "in situ". In situ immune deposit formation may occur at subepithelial, subendothelial, and mesangial sites. In situ immune-complex formation has been most frequently studied in the Heymann nephritis models of membranous nephropathy with subepithelial immune deposits. While the autoantigenic target in Heymann nephritis has been identified as megalin, the pathogenic antigenic target in human membranous nephropathy had been unknown until the recent identification of neutral endopeptidase as one target. It is likely that there is no universal antigen in human membranous nephropathy. Immune complexes can damage glomerular structures by attracting circulating inflammatory cells or activating resident glomerular cells to release vasoactive substances, cytokines, and activators of coagulation. However, the principal mediator of immune complex-mediated glomerular injury is the complement system, especially C5b-9 membrane attack complex formation. C5b-9 inserts in sublytic quantities into the membranes of glomerular cells, where it produces cell activation, converting normal cells into resident inflammatory effector cells that cause injury. Excessive activation of the complement system is normally prevented by a series of circulating and cell-bound complement regulatory proteins. Genetic deficiencies or mutations of these proteins can lead to the spontaneous development of glomerular disease. The identification of specific antigens in human disease may lead to the development of fundamental therapies. Particularly promising future therapeutic approaches include selective immunosuppression and interference in complement activation and C5b-9-mediated cell injury.

Animals↗
PubMed1998

Identity of the residues responsible for the species-restricted complement inhibitory function of human CD59.

The membrane-anchored glycoprotein CD59 inhibits assembly of the C5b-9 membrane attack complex (MAC) of human complement. This inhibitory function of CD59 is markedly selective for MAC assembled from human complement components C8 and C9, and CD59 shows little inhibitory function toward MAC assembled from rabbit and many other non-primate species. We have used this species selectivity of CD59 to identify the residues regulating its complement inhibitory function: cDNA of rabbit CD59 was cloned and used to express human/rabbit CD59 chimeras in murine SV-T2 cells. Plasma membrane expression of each CD59 chimera was quantified by use of a 5'-TAG peptide epitope, and each construct was tested for its ability to inhibit assembly of functional MAC from human versus rabbit C8 and C9. These experiments revealed that the species selectivity of CD59 is entirely determined by sequence contained between residues 42 and 58 of the human CD59 polypeptide, whereas chimeric substitution outside this peptide segment has little effect on the MAC inhibitory function of CD59. Substitution of human CD59 residues 42-58 into rabbit CD59 resulted in a molecule that was functionally indistinguishable from native human CD59, whereas the complementary construct (corresponding residues of rabbit CD59 substituted into human CD59) was functionally indistinguishable from rabbit CD59. Based on the solved solution structure of CD59, these data suggest that selectivity for human C8 and C9 resides in a cluster of closely spaced side chains on the surface of CD59 contributed by His44, Asn48, Asp49, Thr51, Thr52, Arg55, and Glu58 of the polypeptide.

Amino Acid Sequence↗
PubMed1993

Complement activation during CAPD.

Complement activation was monitored in 20 CAPD patients and 20 normal individuals using markers of the alternative (Bb fragment), classical (C4d fragment), common (iC3b) and terminal pathways (SC5b-9, the soluble form of the membrane attack complex, MAC), together with C3, C4 and factor B. CAPD plasma SC5b-9 was higher than normal although this was not due to increased complement activation in the plasma. The calculated cleavage for C3, C4 and factor B to iC3b, C4d and Bb respectively, due to spontaneous activation, was similar in both groups. C3, C4 and factor B in dialysate were less than 1% of plasma concentration, consistent with vascular leakage, whereas iC3b, Bb and SC5b-9 were at higher concentrations, suggesting generation in the peritoneum by the alternative pathway. 2.4% C4d is consistent with leakage of this small molecule but may indicate slight classical activation. It is concluded that complement activation occurs in the peritoneum during CAPD. MAC and the anaphylatoxins which are also generated may contribute to an increased risk of infection and other inflammatory complications.

Blood↗
PubMed1995

Protection of retroviral vector particles in human blood through complement inhibition.

The rapid inactivation of murine-derived retroviral vectors in human or nonhuman primate sera is largely attributed to the activity of complement mediated through the classical pathway. In this study, we have further investigated the relationship between the human complement cascade and retrovirus inactivation. Preincubation in normal human serum effectively inactivated LXSN retroviral vector particles, whereas the vector maintained the ability to transduce cells following incubation in sera deficient in either the C1, C2, C3, C5, C6, C8, or C9 human complement proteins. Preincubation of serum with monoclonal antibodies (mAbs) that functionally block specific complement components, including C5, C6, C8, and C9, successfully protected the LXSN vector from complement-mediated inactivation. Treatment of serum with cobra venom factor, which consumes terminal complement, also effectively protected the vector from inactivation. LXSN vector survival in serum corresponded inversely to the level of complement activity following treatment of serum with anti-C5 mAb as assessed in an erythrocyte hemolytic assay. Additionally, pretreatment of human whole blood with anti-C5 mAb effectively inhibited inactivation of the LXSN vector. Taken together, these data demonstrate that formation of the membrane attack complex (MAC, C5b-9) is required for the inactivation of the murine-based LXSN retroviral vector in human blood and that this process can be abrogated with the use of soluble complement inhibitors.

3T3 Cells↗
PubMed1999

Hyperacute rejection in the guinea pig-to-rat model without formation of the membrane attack complex.

The guinea pig (GP)-to-rat transplantation model has been widely used to study hyperacute rejection (HAR) of xenografts. In this model heart graft survival beyond 8 days has never been reported. In contrast, survival times of kidney and heart grafts up to 62 days have been reported in the discordant pig-to-primate model. It is not clear why it is so much more difficult to obtain long-term graft survival in the GP-to-rat model as compared to the pig-to-primate model. We hypothesized that mechanisms other than activation of complement may be involved in the rejection of guinea pig grafts by rat recipients. Therefore, we have studied in detail the rejection of GP aortic grafts by rat recipients, either PVG/c+ (complement competent, group 1), or PVG/c- (complement C6 deficient, group 2). PVG/c- rats are not able to form the membrane attack complex (MAC) of complement. Forty-four GP-to-rat aortic transplantations were performed successfully. Recipient rats were sacrificed at various intervals after transplantation (4, 24 and 48 h, and 7 and 28 days, three to six animals per time point per group). Twenty-four hours after transplantation the number of cells in the media was significantly decreased from 11.1 +/- 0.9 cells/mm2 to 3.1 +/- 2.8 cells/mm2 in group 1, whereas the number of medial cells in group 2 remained the same. The number of medial cells was significantly decreased in both groups at 48 h post-transplantation (group 1: 1.8 +/- 2.2 cells/mm2; group 2: 5.5 +/- 3.0 cells/mm2). At that time no infiltrating cells were apparent in the grafts of either two groups. Seven days after transplantation, the number of medial cells remained low in group 1 (1.8 +/- 2.9 cells/mm2) but was increased in group 2 (10.7 +/- 2.6 cells/mm2) as a consequence of infiltrating immune cells. These infiltrating cells consisted mainly of macrophages, but also T cells and NK cells. At 28 days after transplantation the grafts in both groups were completely reorganized and no distinction could be made between media and adventitia. These results show that rejection of GP grafts by rat recipients can occur in the absence of both MAC of complement and immune competent cells. This MAC and immune cells independent type of rejection has not been described before and may explain the difficulty in obtaining long-term graft survival in the GP-to-rat xenotransplantation model.

Acute Disease↗
PubMed2004

Critical protection from renal ischemia reperfusion injury by CD55 and CD59.

Renal ischemia-reperfusion injury (IRI) is a feature of ischemic acute renal failure and it impacts both short- and long-term graft survival after kidney transplantation. Complement activation has been implicated in renal IRI, but its mechanism of action is uncertain and the determinants of complement activation during IRI remain poorly understood. We engineered mice deficient in two membrane complement regulatory proteins, CD55 and CD59, and used them to investigate the role of these endogenous complement inhibitors in renal IRI. CD55-deficient (CD55(-/-)), but not CD59-deficient (CD59(-/-)), mice exhibited increased renal IRI as indicated by significantly elevated blood urea nitrogen levels, histological scores, and neutrophil infiltration. Remarkably, although CD59 deficiency alone was inconsequential, CD55/CD59 double deficiency greatly exacerbated IRI. Severe IRI in CD55(-/-)CD59(-/-) mice was accompanied by endothelial deposition of C3 and the membrane attack complex (MAC) and medullary capillary thrombosis. Complement depletion in CD55(-/-)CD59(-/-) mice with cobra venom factor prevented these effects. Thus, CD55 and CD59 act synergistically to inhibit complement-mediated renal IRI, and abrogation of their function leads to MAC-induced microvascular injury and dysfunction that may exacerbate the initial ischemic assault. Our findings suggest a rationale for anti-complement therapies aimed at preventing microvascular injury during ischemia reperfusion, and the CD55(-/-)CD59(-/-) mouse provides a useful animal model in this regard.

Animals↗
PubMed1982

Complement activation by isolated myelin: activation of the classical pathway in the absence of myelin-specific antibodies.

Many pathological conditions of the central nervous system involve damage to and removal of myelin membrane. Very little is known about initiation of this membrane damage and the mechanisms of disposal of the damaged tissue. We are interested in the interaction between complement (the components of complement are designated C1, C2, C3, etc.) and myelin membranes and the possible role of complement in amplifying myelin damage and in the disposal of damaged myelin in vivo, because activation of complement generates both membrane-attack complexes and opsonin(s). In this study, we found that isolated rat or human myelin consumes complement in the absence of specific antibodies. Activation of complement was demonstrated by showing C3 cleavage in fresh serum incubated with myelin. Incubation of central nervous system myelin with C2-deficient serum produced no C3 consumption and only minor factor B conversion, thus excluding the alternative pathway of activation. Involvement of the classical pathway was shown directly by the C1 fixation and transfer assay. Myelin incubated with C2-deficient serum or with purified C1 and then washed contained C1 activity that could lyse sheep erythrocytes sensitized with anti-Forssman IgM antibody and carrying C4, together with C2 and C3-C9. Membranes in brain tissues other than myelin (heavy membrane fraction obtained on sucrose density gradient centrifugation) were unable to activate C1.

Animals↗
PubMed2005

CD46 plays a key role in tailoring innate immune recognition of apoptotic and necrotic cells.

Complement is the canonical innate immune system involved in host defense and tissue repair with the clearance of cell debris. In contrast to the robust armory mounted against microbial nonself-pathogens, complement is selectively activated on altered self (i.e. apoptotic and necrotic cells) to instruct the safe demise by poorly characterized mechanisms. Our data shed new light on the role of complement C1q in sensing nucleic acids (NA) rapidly exposed on apoptotic Jurkat T cell membranes and in driving C3 opsonization but without the lytic membrane attack complex. DNA/RNase-treated apoptotic cells failed to activate complement. We found that several other apoptotic cell models, including senescent keratinocytes, ionophore-treated sperm cells, and CMK-derived platelets, stained for cleaved caspase 3 were rapidly losing the key complement regulator CD46. CD46 from nuclear and membrane stores was found to cluster into blebs and shed into microparticles together with NA, phosphatidylserine, C1q, and factor H. Classical and alternative pathways of complement were involved in the recognition of H2O2-treated necrotic cells. Membrane attack complex was detected on necrotic cells possibly as a result of CD46 and CD59 shedding into soluble forms. Our data highlight a novel and universal paradigm whereby the complement innate immune system is using two synergistic strategies with the recognition of altered self-NA and missing self-CD46 signals to instruct and tailor the efficient removal of apoptotic and necrotic cells in immunoprivileged sites.

Apoptosis↗
PubMed2006

Inhibition of classical complement activation attenuates liver ischaemia and reperfusion injury in a rat model.

Activation of the complement system contributes to the pathogenesis of ischaemia/reperfusion (I/R) injury. We evaluated inhibition of the classical pathway of complement using C1-inhibitor (C1-inh) in a model of 70% partial liver I/R injury in male Wistar rats (n = 35). C1-inh was administered at 100, 200 or 400 IU/kg bodyweight, 5 min before 60 min ischaemia (pre-I) or 5 min before 24 h reperfusion (end-I). One hundred IU/kg bodyweight significantly reduced the increase of plasma levels of activated C4 as compared to albumin-treated control rats and attenuated the increase of alanine aminotransferase (ALT). These effects were not better with higher doses of C1-inh. Administration of C1-inh pre-I resulted in lower ALT levels and higher bile secretion after 24 h of reperfusion than administration at end-I. Immunohistochemical assessment indicated that activated C3, the membrane attack complex C5b9 and C-reactive protein (CRP) colocalized in hepatocytes within midzonal areas, suggesting CRP is a mediator of I/R-induced, classical complement activation in rats. Pre-ischaemic administration of C1-inh is an effective pharmacological intervention to protect against liver I/R injury.

Alanine Transaminase↗
PubMed2006

Complement activation via alternative pathway is critical in the development of laser-induced choroidal neovascularization: role of factor B and factor H.

The objective of this study was to explore the role of classical, lectin, and alternative pathways of complement activation in laser-induced choroidal neovascularization (CNV). The classical and alternative pathways were blocked in C57BL/6 mice by small interfering RNAs (siRNA) directed against C1q and factor B, respectively. C4(-/-) mice developed CNV similar to their wild-type controls and inhibition of C1q by siRNA had no effect on the development of CNV. In contrast, CNV was significantly inhibited (p < 0.001) in C5(-/-) mice and C57BL/6 mice treated with factor B siRNA. Inhibition of the alternative pathway by factor B siRNA resulted in decreased levels of membrane attack complex and angiogenic factors-vascular endothelial growth factor and TGF-beta2. Furthermore, factor B was up-regulated in complement sufficient C57BL/6 mice at day 1 postlaser and remained elevated at day 7. Significantly reduced levels of factor H were observed at day 3 in these animals. In conclusion, our results demonstrate that activation of the factor B-dependent alternative pathway, but not the classical or lectin pathways, was essential for the development of CNV in mouse model of laser-induced CNV. Thus, specific blockade of the alternative pathway may represent a therapeutically relevant strategy for the inhibition of CNV.

Animals↗
PubMed1995

Human CD59 expressed in transgenic mouse hearts inhibits the activation of complement.

Porcine-to-human xenotransplantation offers a potential solution to the critical shortage of human organs. The major immunological barrier to xenotransplantation between these species is a rapid rejection process mediated by preformed natural antibodies and complement. Xenogeneic organ grafts are especially susceptible to complement mediated injury because complement regulatory proteins, which ordinarily protect cells from inadvertent injury during the activation of complement, function poorly in regulating activation of heterologous complement. Removal of xenoreactive antibodies or systemic inhibition of complement activity has been shown to prolong graft survival. As an alternative to the systemic inhibition of complement activity, we have established a model system using transgenic animals to test whether the expression of human membrane bound complement regulatory proteins on mouse endothelial cells can inhibit the activation of human complement. CD59, which acts at the terminal stage of complement activation by inhibiting the formation of the membrane attack complex, was used as a paradigm for this model. A CD59 construct containing the putative CD59 gene promoter linked to the CD59 coding region was used to demonstrate expression of the human CD59 protein in various tissues of transgenic mice, including endothelial cells in the heart. In addition, we show that the transgenic CD59 protein is biologically active as determined by the ability to inhibit the formation of membrane attack complex in transgenic mouse hearts perfused ex vivo with human plasma. These results demonstrate that expression of membrane bound complement regulatory proteins can achieve complement inhibition in a xenogeneic organ and suggest that this approach may be useful for successful xenotransplantation between discordant species.

Animals↗