Activity and activation of the complement system in patients being operated on for cancer of the colon

OBJECTIVE

To find out if there was any local activation of complement in the vicinity of a colonic cancer, and any fluctuation in the function of the complement system during operation.

DESIGN

Prospective study.

SETTING

One university and two district hospitals in Denmark.

SUBJECTS

29 selected patients undergoing emergency and elective operations for colonic cancer.

INTERVENTIONS

Measurements of systemic and local complement fixation capacity and complement activation in samples of serum or plasma taken before, during, and after operation.

MAIN OUTCOME MEASURES

Changes in complement fixation capacity and complement activation during operation.

RESULTS

Haemodilution during operation caused a significant reduction in the complement fixation capacity of serum and in the activation of the complement system as measured by generation of C3c. We were unable to confirm the presence of complement inhibitors during operation. Haemodilution caused a 30% reduction in fixation capacity of C3b (12/29 samples of serum had values more than 2SD below the mean of the reference range compared with 4/29 before operation). The activity of C4 was reduced by 25% during operation and the capacity of the complement system to fix C3b and C4b was restored to baseline nine days postoperatively. Concentration of C3d was significantly higher in serum from tumour venous blood compared with that from peripheral blood during operation.

CONCLUSION

The presence of complement activation products in the general circulation reflects local activation of the complement system in the vicinity of the tumour, but this may have been influenced by tissue necrosis or subclinical infection. Haemodilution causes a significant reduction in the capacity of the complement system during operation, whereas inhibitory factors associated with the cancer or operation and anaesthesia could not be demonstrated. We found no correlation between complement activity and clinical data.

Expression of the complement regulatory protein CD59 on human spermatozoa: characterization and role in gametic interaction

Protectin (CD59) is a complement regulatory protein which blocks the membrane attack complex during complement activation. CD59 was identified on the human sperm surface by means of H19, an IgG1 anti-protectin mouse monoclonal antibody. Using indirect immunofluorescence, flow cytometry and immunoperoxidase, CD59 was found to be present on the whole plasma membrane including the head and tail of fresh ejaculated, capacitated and acrosome-reacted spermatozoa. Immunoperoxidase staining of normal testicular sections indicated that this protein was already present on intraluminal germ cells. Analysis of this sperm protein by gel electrophoresis and immunoblotting revealed that its molecular weight of 20 kDa was comparable to that of CD59 expressed on peripheral blood cells (erythrocytes, lymphocytes) and that it was bound to the membrane through a glycophospholipid tail which could be released after treatment with phosphatidylinositol-specific phospholipase C. Associated to membrane cofactor protein (CD46) and decay accelerating factor (CD55) located in the acrosomal membranes, CD59 may participate to the protection of male gametes against complement-mediated damage as they travel through the female genital tract. Moreover CD59, known as an adhesion molecule involved in lymphocyte rosettes, may also participate in cell to cell adhesion during gametic interaction since H19 inhibited sperm binding and reduced the penetration rate and index during the hamster egg penetration test.

Role of CD59 in experimental glomerulonephritis in rats

CD59 is a molecule which is present on the host cell membranes and inhibits formation of membrane attack complex. A monoclonal antibody, 6D1, recognizes a rat analogue of human CD59. 6D1 inhibits function of rat CD59 and can enhance complement-mediated hemolysis in vitro. To assess the role of CD59 in complement-mediated glomerular injury, 6D1 was tested in a model of experimental glomerulonephritis induced by a lectin and its antibodies. The left kidney of a rat was perfused either with 200 micrograms of Lens culinaris hemagglutinin (LCH) plus 1 mg of 6D1 (IgG1 fraction) (Group I and III) or with LCH only (Group II) through a cannula placed in the left renal artery. All the perfusate was discarded from a cannula in the renal vein. The holes in the artery and vein were repaired by microsurgery and the blood circulation was re-established. Rats were injected either with 0.125 ml of rabbit anti-LCH serum (Group I and II), or with normal rabbit serum (Group III) via tail vein one minute after the recirculation. Fifteen minutes after injection, significant C9 deposition in the glomeruli was observed only in Group I, whereas C3 deposition in Group I and II were comparable. At Day 4, total glomerular cells, proliferating cells, glomerular expression of intercellular adhesion molecule-1 and fibrin deposition in Group I were all significantly increased when compared with Group II. At Day 7, number of total glomerular cells and leukocytes in the glomeruli of Group I were significantly higher than in Group II. The glomeruli in Group III appeared normal throughout experiments. These data indicate that the functional inhibition of a rat analogue of human CD59 worsens complement-mediated glomerular injury in vivo.

Decay-accelerating factor (CD55), a glycosylphosphatidylinositol-anchored complement regulatory protein, is a receptor for several echoviruses

Echoviruses are human pathogens belonging to the picornavirus family. Decay-accelerating factor (DAF) is a glycosylphosphatidylinositol (GPI)-anchored surface protein that protects cells from lysis by autologous complement. Anti-DAF monoclonal antibodies prevented echovirus 7 attachment to susceptible cells and protected cells from infection. HeLa cells specifically lost the capacity to bind echovirus 7 when treated with phosphatidylinositol-specific phospholipase C, an enzyme that releases GPI-anchored proteins from the cell surface, indicating that the virus receptor, like DAF, is a GPI-anchored protein. Although Chinese hamster ovary cells do not bind echovirus 7, transfectants expressing human DAF bound virus efficiently, and binding was prevented by pretreatment with an anti-DAF monoclonal antibody. Anti-DAF antibodies prevented infection by at least six echovirus serotypes. These results indicate that DAF is the receptor mediating attachment and infection by several echoviruses.

Time course of complement activation and inhibitor expression after ischemic injury of rat myocardium

Activation of the complement (C) system has been documented in both experimental and clinical studies of myocardial infarction, but the exact time course and mechanisms leading to C activation have remained unclear. Our earlier postmortem study on human beings showed that formation of the membrane attack complex (MAC) of C was associated with loss of CD59 (protectin), an important sarcolemmal regulator of MAC, from the infarcted area. The recent discovery of a rat analogue of CD59 has now allowed the first experimental evaluation of the temporal and spatial relationship between C component deposition and loss of CD59 in acute myocardial infarction (AMI). After ligating the left coronary artery in rats the earliest sign of C activation, focal deposition of C3, was observed at 2 hours. Deposition of the early (C1, C3) and late pathway (C8, C9) components in the AMI lesions occurred at 3 hours. Glycophosphoinositol-anchored rat CD59 was expressed in the sarcolemmal membranes of normal cardiomyocytes. In Western blot analysis extracts of normal rat heart CD59 appeared as a band of 21 kd of molecular weight under nonreducing conditions. Loss of CD59 in the AMI lesions was observed in association with deposits of MAC from day one onward. Our results show that C activation universally accompanies AMI in vivo. It is initiated within 2 hours after coronary artery obstruction via deposition of C3, which may be due to generation of the alternative pathway C3 convertase in the ischemic area. Deposition of C1 and late C components also starts during the early hours (2 to 4 hours) after ischemia. Subsequent loss of the protective CD59 antigen may initiate postinjury clearance of the irreversibly damaged tissue.

Structure and function of decay accelerating factor CD55

Studies of decay-accelerating factor (DAF) function and structure are reviewed. DAF was first recognized as a species restricting factor operating at the level of C3/C5 activation. Cloning of the gene indicates that DAF has four short consensus repeats of the type characteristic of the regulators of complement activation gene cluster family. The third short consensus repeat is responsible for DAF's complement regulatory activity and signaling. DAF, like other glycophosphatidylinositol (GPI) anchored proteins, is associated with tyrosine kinases, and these kinases are probably the signaling devices. The details of how DAF's GPI anchor in the outer leaflet of plasma membrane connects with the tyrosine kinases on the inner leaflet are not known. Although DAF does not have an essential role in controlling hemolysis of erythrocytes, it does have important role in regulating the deposition of C3 on nucleated cells. The therapeutic potential of DAF is discussed.

Upregulation of complement regulators MCP (CD46), DAF (CD55) and protectin (CD59) in arthritic joint disease

CD46, CD55 and CD59 are cell surface glycoproteins which are widely distributed on normal tissue, where they function in the prevention of complement-mediated damage. In this study we have investigated the altered expression of these molecules under inflammatory conditions both in vitro and in vivo. By using immunocytochemical techniques we demonstrated marked but disparate upregulation of these molecules in IL1-treated cartilage and in diseased cartilage from arthritic joints compared to normal cartilage in both humans and pigs. Expression of these proteins was restricted to the chondrocyte surface, and was also demonstrated on isolated chondrocytes grown in monolayer culture and stimulated with IL1. It is suggested that the elevated levels of these regulatory proteins may be necessary to ameliorate the multiple damaging effects of the inflammatory processes associated with destructive joint diseases.

Membrane defence against complement lysis: the structure and biological properties of CD59

The complement system is an important branch of the innate immune response, constituting a first line of defence against invading microorganisms which activate complement via both antibody-dependent and -independent mechanisms. Activation of complement leads to (a) a direct attack upon the activating cell surface by assembly of the pore-forming membrane attack complex (MAC), and (b) the generation of inflammatory mediators which target and recruit other branches of the immune system. However, uncontrolled complement activation can lead to widespread tissue damage in the host, since certain of the activation products, notably the fragment C3b and the C5b-7 complex, can bind nonspecifically to any nearby cell membranes. Therefore it is important that complement activation is tightly regulated. Our own cells express a number of membrane-bound control proteins which limit complement activation at the cell surface and prevent accidental complement-mediated damage. These include decay-accelerating factor, complement receptor 1 and membrane cofactor protein, all of which are active at the level of C3/C5 convertase formation. Until recently, cell surface control of MAC assembly had been attributed to a single 65-kD membrane protein called homologous restriction factor (alternatively named C8-binding protein and MAC-inhibiting protein). However a second MAC-inhibiting protein has since been discovered and it is now clear that this protein plays a major role in the control of membrane attack. This review charts the rapid progress made in elucidating the protein and gene structure, and the mechanism of action of this most recently discovered complement inhibitor, CD59.

The possible role of membrane complement regulators in vasculitis

Potentially, damage to endothelial cells of small vessel walls may be induced by the deposition of immune complexes and subsequent complement activation. The degree of deposition of C3b onto the endothelial cell surface under normal conditions is regulated by a number of membrane-bound regulators. Under inflammatory conditions various cytokines could potentially deregulate the expression and function of the membrane-bound complement inhibitors. Such a process could potentially increase the susceptibility of the endothelial cell layer to complement-mediated attack and provoke a vascular lesion.

Regulation of complement activity by vaccinia virus complement-control protein

A major protein secreted by vaccinia virus-infected cells has structural similarity to the super-family of complement-control proteins. This vaccinia complement-control protein (VCP) was studied to determine how it regulates complement activation. VCP was bound by C4b and C3b and served as a cofactor with factor I in cleaving these two molecules. VCP inhibited the formation and accelerated the decay of the classical C3 convertase. It also accelerated decay of the alternative pathway convertase, although higher concentrations were apparently needed. In vitro, therefore, VCP interfered with the classical and alternative complement pathways at several steps. In vivo, this interference may increase the virulence of vaccinia virus by enabling it to escape attack by the host's complement system.

Relative roles of decay-accelerating factor, membrane cofactor protein, and CD59 in the protection of human endothelial cells against complement-mediated lysis

Human umbilical vein endothelial cells (HUVEC) were found by Western blot analysis to express three membrane-bound C regulatory proteins, decay-accelerating factor (DAF), membrane cofactor protein (MCP) and CD59. DAF was detected on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a 70-kDa molecule under nonreducing conditions in 2% deoxycholate extracts of HUVEC, MCP as a 63-kDa protein and CD59 as a 20-kDa molecule. Northern blot analysis revealed the presence of two species of mRNA expressed in HUVEC, which hybridized to a cDNA probe specific for DAF, with sizes of about 2.0 kb and 2.7 kb. MCP mRNA was detected at 4.2 kb and a CD59 cDNA probe hybridized with three mRNA species with sizes of about 800, 1400 and 2000 bp. DAF and CD59 were released from the surface of HUVEC by phosphatidylinositol-phospholipase C, demonstrating that both are attached to the cell membrane by means of a glycolipid anchor. The relative contribution of DAF, MCP and CD59 in regulating the sensitivity to lysis of HUVEC by autologous complement was determined by incubation of sensitized endothelial cells with F(ab')2 fragments of polyclonal antibodies raised against these proteins. The susceptibility of sensitized cells to lysis by homologous complement was markedly increased in the presence of F(ab')2 anti-CD59 and to a lesser, but significant, extent in the presence of F(ab')2 anti-DAF. F(ab')2 anti-MCP did not significantly alter the susceptibility of HUVEC to complement-mediated lysis.

The complement system in human reproduction

Regulation of the complement system in reproduction is unique inasmuch as reproductive tissues represent the only condition where allogeneic interactions occur naturally. Both allogeneic extraembryonic membranes and semen that contact and interact with maternal cells and tissues must avert complement-mediated damage to ensure reproductive success. Several regulators of complement activation exist. Membrane cofactor protein (MCP) and decay accelerating factor (DAF) inactivate C3 and C5 convertases on cell surfaces. In addition, CD59 inhibits the membrane attack complex (MAC) of the complement cascade. Strong expression of these membrane glycoproteins by trophoblast and amniotic epithelium has been observed. MCP, DAF, and CD59 likely safeguard extraembryonic tissues from complement damage originating from maternal and fetal blood or amniotic fluid. Different reproductive tract fluids vary in complement levels. With the exception of ovarian follicular fluid, these levels are generally much less than those in blood. Endometrial and cervical content of C3 appear to be regulated by hormones. These observations suggest that the effects of complement activation may vary in reproductive tissues. MCP is absent from the surfaces of oocytes. Sperm express MCP and DAF in discrete areas that would not be associated with the known complement-regulatory functions of these proteins. Seminal plasma contains MCP and the MAC inhibitor SP-40,40 but not DAF.SP-40,40 may exemplify how complement-regulatory proteins perform alternative functions as it interacts with molecules other than complement components. We have reviewed aspects of the complement system that relate to allogeneic interactions in reproduction and that suggest fruitful areas for further research.

Presence of human chromosome 1 with expression of human decay-accelerating factor (DAF) prevents lysis of mouse/human hybrid cells by human complement

Xenogeneic organs transplanted to phylogenetically distant species are subject to rapid destruction mediated by complement. In humans, the complement activation is regulated by several proteins encoded by a series of closely linked genes (RCA locus) located on chromosome 1. The mouse/human hybrid cell line B10 was found to have retained human chromosome 1. FACS analysis confirmed that RCA products such as decay-accelerating factor (DAF) were expressed on the membrane surface of B10 cells. When exposed to human or rabbit complement in the presence of 'naturally occurring' human anti-mouse antibodies these cells were not lysed by human complement but were killed by rabbit complement. This effect could be abrogated by addition of anti-DAF monoclonal antibody (IC6). The results offer potential for genetic manipulation of the human complement regulatory products in animals to overcome xenograft hyperacute rejection.

Role of human decay-accelerating factor in the evasion of Schistosoma mansoni from the complement-mediated killing in vitro

Decay-accelerating factor (DAF) is a 70-kD membrane glycoprotein that prevents complement (C)-mediated hemolysis by blocking the assembly or accelerating the decay of C3 convertase. Purified DAF is known to incorporate into the membrane of DAF-deficient cells, inhibiting lysis. Since Schistosoma mansoni is a blood-dwelling parasite, we investigated whether DAF can be transferred from human erythrocytes to the worm and protect it against C-mediated killing in vitro. We have found that schistosomula (schla) incubated with normal human erythrocytes (N-HuE), but not with DAF-deficient erythrocytes, become resistant to C damage in vitro. Protected parasites acquire a 70-kD surface protein which can be immunoprecipitated by anti-DAF antibodies. The acquired resistance is abrogated by treatment of N-HuE-incubated parasites with anti-DAF antibody. These results indicate that, in vitro, N-HuE DAF can be transferred to schla, and suggest its participation in preventing their C-mediated killing. This could represent an important strategy of parasites to evade the host's immune response in vivo.

Molecular basis of the enhanced susceptibility of the erythrocytes of paroxysmal nocturnal hemoglobinuria to hemolysis in acidified serum

When incubated in acidified serum, the erythrocytes of paroxysmal nocturnal hemoglobinuria (PNH) are hemolyzed through activation of the alternative pathway of complement (APC), but normal erythrocytes are resistant to this process. PNH cells are deficient in decay-accelerating factor (DAF), a complement regulatory protein that inhibits the activity of both the classical and the alternative pathways. However, deficiency of DAF alone does not account entirely for the aberrant effects of acidified serum on PNH cells. Recently, we have shown that PNH erythrocytes are also deficient in another complement control protein called membrane inhibitor of reactive lysis (MIRL) that restricts complement-mediated lysis by blocking formation of the membrane attack complex (MAC). To determine the effects of the DAF and MIRL on susceptibility to acidified serum lysis, PNH cells were repleted with the purified proteins. DAF partially inhibited acidified serum lysis by blocking the activity of the amplification C3 convertase. MIRL inhibited acidified serum lysis both by blocking the activity of the MAC and by inhibiting the activity the C3 convertase. When DAF function was blocked with antibody, normal erythrocytes became partially susceptible to acidified serum lysis. By blocking MIRL, cells were made completely susceptible to lysis, and control of C3 convertase activity was partially lost. When both DAF and MIRL were blocked, the capacity of normal erythrocytes to control the activity of the APC and the MAC was destroyed, and the cells hemolyzed even in unacidified serum. These studies demonstrate that DAF and MIRL act in concert to control susceptibility to acidified serum lysis; of the two proteins, MIRL is the more important. In addition to its regulatory effects on the MAC, MIRL also influences the activity of the C3 convertase of the APC. Further, in the absence of DAF and MIRL, the plasma regulators (factor H and factor I) lack the capacity to control membrane-associated activation of the APC.

Phospholipid-anchored and transmembrane versions of either decay-accelerating factor or membrane cofactor protein show equal efficiency in protection from complement-mediated cell damage

Decay-accelerating factor (DAF) is a glycosyl-phosphatidylinositol (GPI)-anchored membrane protein that protects cells from complement-mediated damage by regulation of the C3 convertase. To investigate the role of the GPI anchor in the function of DAF, the cDNA encoding human DAF was expressed by transfection in Chinese hamster ovary (CHO) cells. Testing of these DAF transfectants in an antibody plus human complement-mediated cytotoxicity assay demonstrated that DAF protects these cells from cytotoxicity, and that the level of protection increases with expression of surface DAF. A cDNA construct encoding a transmembrane version of DAF (DAF-TM) protects CHO transfectants from cytotoxicity with equal efficiency to DAF. This DAF-TM construct used the TM and cytoplasmic domains of membrane cofactor protein (MCP); an alternate TM version of DAF constructed with the TM and cytoplasmic domains of HLA-B44 showed equivalent protection. The protection from cytotoxicity involved a decrease in the deposition of C3 on the cell, consistent with the effect of DAF on the C3 convertase. A second pair of anchor variants, MCP and a GPI-anchored construct, MCP-PI, were also equivalent in their complement protection. The equivalent function of GPI-anchored and TM versions of a protein was not expected based on the hypothesized increased lateral mobility of GPI-anchored proteins, which should confer a functional advantage in contacting ligand, in this case, C3b or C4b, on the cell surface. These data suggest either that GPI-anchored and TM versions of a protein have equal lateral mobility in the membrane, or else that increased lateral mobility is not advantageous to DAF or MCP in carrying out their complement inhibitory roles. Furthermore, DAF and MCP demonstrated approximately equal protection of cells from complement-mediated cytotoxicity, suggesting that DAF and MCP provide overlapping levels of protection to cells against damage mediated by the complement system.

Induction of the paroxysmal nocturnal hemoglobinuria phenotype in normal human erythrocytes: effects of 2-aminoethylisothiouronium bromide on membrane proteins that regulate complement

To investigate the mechanism by which treatment of normal human erythrocytes with the sulfhydryl reagent 2-aminoethylisothiouronium bromide (AET) induces susceptibility to complement mediated lysis, the effects of AET on the structural and functional integrity of decay accelerating factor (DAF), membrane inhibitor of reactive lysis (MIRL), and complement receptor type 1 (CR1) were examined. Following treatment with AET, erythrocyte MIRL and CR1 were no longer recognized in situ by antibodies, and antibody binding to DAF was diminished by approximately 50%. These studies indicated that the structural integrity of the three complement regulatory proteins was either partially (DAF) or completely (MIRL and CR1) disrupted by AET. Subsequent experiments showed that functional inactivation paralleled the structural disruption. Treatment of normal erythrocytes with AET induced susceptibility to cobra venom factor-initiated hemolysis, indicating that the functional activity of MIRL had been destroyed. The capacity of erythrocyte CR1 to serve as a cofactor for factor I-mediated cleavage of iC3b to C3c and C3dg was lost following treatment with AET. C3 convertase activity increase markedly following treatment of erythrocytes with AET, but convertase activity on AET cells was approximately 50% less than that observed when DAF function on normal cells was completely inhibited by antibody. Susceptibility of AET cells to acidified serum lysis was shown to be due primarily to inactivation of MIRL. Unexpectedly, in acidified serum the activity of the amplification C3 convertase of the APC was found to be controlled by MIRL as well as by DAF. These studies show that AET induces susceptibility to complement-mediated lysis by disrupting the structural and functional integrity of membrane constituents that regulate the activity of both the C3 convertases and the membrane attack complex of complement.

Reduced activity of DAF on complement enzymes bound to alternative pathway activators. Similarity with Factor H

Attachment of C3b to activators of the alternative pathway of complement results in a decrease in regulatory activity expressed by Factor H. Decay-accelerating factor (DAF) and Factor H were found to exhibit quantitatively similar decreases in regulatory activity toward the C3 convertase (C3b,Bb) bound to activators, such as zymosan (Zym) and rabbit erythrocytes (ER), compared to non-activators, such as sheep (ES) and bovine (EB) erythrocytes. Purified DAF and Factor H, in 0.1% NP-40, were assayed by measuring the amount required to release 50% of the radiolabelled Bb in 10 min from C3b,Bb on Zym or cross-linked erythrocytes. The relative effectiveness (i.e. the restriction index, RI) of DAF for accelerating the decay of C3b,Bb on the various particles was: ES (1.0), ER (0.04) and Zym (0.03). The RI for Factor H was: ES (1.0), ER (0.04) and Zym (0.07). The rate of decay of C3b,Bb induced by DAF and Factor H showed similar restriction. The results suggest that the regulatory properties of DAF are reduced if the cells on which it resides become activators of the alternative pathway as a result of transformation, virus infection or surface alteration. These findings may explain reports of dysfunctional DAF on alternative pathway-activating cells.

The influence of membrane components on regulation of alternative pathway activation by decay-accelerating factor

Decay-accelerating factor (DAF) is a C regulatory protein which functions in membranes to inhibit autologous C activation on cell surfaces. A liposome model was used to study the mechanism of DAF action and examine the effects of membrane-bound glycophorin and LPS on the regulatory activity of DAF. Liposomes were incubated in MgEGTA-treated human serum and activation of the alternative pathway measured by C3b binding. Liposomes composed of phosphatidylcholine, phosphatidylethanolamine, and cholesterol activated the alternative pathway in proportion to their content of PE. Incorporation of 10(-7) mol/mol phospholipid of either human E or HeLa cell-derived DAF inhibited C activation by liposomes containing 40% phosphatidylethanolamine by 50%, an efficiency comparable to that observed in intact E. HeLa DAF that had been treated with phosphatidylinositol-specific phospholipase C to remove its glycolipid anchor had no effect on C activation by liposomes at concentrations as high as 10(-5) mol/mol phospholipid. Incorporation of DAF into liposomes prepared with bound C3b inhibited the deposition of additional C3b by C3bBbP. However, the incorporated DAF increased the amount of Bb generated from B in the presence of D indicating that accelerated decay of the convertase was the primary effect of DAF. Similarly, treatment of intact human E with anti-DAF decreased the amount of Bb generated by the alternative pathway convertase. To study the effects of other membrane components on DAF activity, liposomes were prepared with purified human glycophorin A or LPS. In glycophorin liposomes the presence of PE was required to activate the alternative pathway and DAF inhibited this activation. In contrast, LPS liposomes bound C3b independently of PE and the incorporation of DAF had no effect. These results demonstrate that within a membrane, DAF's inhibitory activity on the alternative pathway C3 convertase is mediated independently of other membrane proteins, that in this model the major activity of DAF is to accelerate convertase decay, and that the presence of other membrane molecules that may serve as C3 acceptors can circumvent DAF function.