Complement resistance of tumor cells: basal and induced mechanisms

Clinical and experimental studies have suggested that complement may play a role in tumor cytotoxicity. However, the efficiency of complement-mediated tumor cell lysis is hampered by various protective mechanisms, which may be divided into two categories: basal and induced mechanisms. The basal mechanisms are spontaneously expressed in cells without a need for prior activation, whereas the induced mechanisms develop in cells subjected to stimulation with cytokines, hormones, drugs or with sublytic doses of complement and other pore-formers. Membrane-associated complement regulatory proteins, such as CD55 (DAF, Decay-Accelerating Factor), CD46 (MCP, Membrane Cofactor Protein), CD35 (CR1, Complement Receptor type 1) and CD59, which serve as an important mechanism of self protection and render autologous cells insensitive to the action of complement. appear to be over-expressed on certain tumors. Furthermore, tumor cells secrete several soluble complement inhibitors. Tumor cells may also express proteases that degrade complement proteins, such as C3, or ecto-protein kinases which can phosphorylate complement components, such as C9. Besides this basal resistance, nucleated cells resist, to some extent, complement damage by removing the membrane attack complexes (MAC) from their surface. Several biochemical pathways, including protein phosphorylation, activation of G-proteins and turnover of phosphoinositides have been implicated in resistance to complement. Calcium ion influx and activation of protein kinase C (PKC) and of mitogen-activated protein kinase (MAPK) have also been demonstrated to be associated with the complement-induced enhanced resistance to lysis. The complete elucidation of the molecular mechanisms involved in basal and induced tumor cell resistance will enable the development of strategies for interfering with these evasion mechanisms and the use of the cytotoxic complement system against tumor cells.

Neutrophil priming by cytokines and vitamin D binding protein (Gc-globulin): impact on C5a-mediated chemotaxis, degranulation and respiratory burst

At the site of acute inflammation, leukocytes are confronted with multiple mediators which are expected to modulate each other with respect to cell responses to the individual ligand. Previous contact of neutrophils with pro-inflammatory cytokines, such as TNF-alpha or GM-CSF, or with the vitamin D binding protein (Gc-globulin) leads to the alteration of either multiple or rather distinct C5a-mediated neutrophil functions. Gc-globulin, the transport protein for 25-(OH)-D3, serves selectively as a cochemotactic factor for C5a/Ca(des)Arg. In contrast, TNF-alpha and GM-CSF, previously shown to modulate FMLP-induced neutrophil responses, are able to reduce C5a-mediated neutrophil chemotaxis, but augment their degranulation and respiratory burst activity. Cytokine priming was shown to be accompanied by a down-regulation of C5a receptors (CD88) whereas vitamin D binding protein had no impact on the level of neutrophil C5a receptors. C5a itself diminishes chemotaxis as well as degranulation and oxidative burst in response to a second dose of the same ligand (homologous desensitization). A similar effect, termed heterologous desensitization, occurs, if cell responses to a given mediator (e.g. to C5a) are reduced or even abolished upon the activation of another receptor of the same G-protein coupled chemoattractant receptor subfamily (e.g. receptors for FMLP or IL-8). In concert with C5a, certain molecules may either augment chemotaxis or shift neutrophil effector functions from migration to exocytosis, an essential step within the sequence of events in a coordinated inflammatory response.

Neutralization of complement regulatory proteins augments lysis of breast carcinoma cells targeted with rhumAb anti-HER2

The capacity of recombinant human monoclonal anti-p185HER2 IgG (rhumAb anti-HER2) to activate human complement was investigated. Complement activation by rhumAb anti-HER2 on various human breast carcinoma cell lines resulted in deposition of complement proteins on these cells. Complement activation was also observed in a solid-phase binding assay, in which purified p185HER2 was immobilized onto a microtiter plate. rhumAb anti-HER2 induced some complement-mediated tumor cell lysis by rabbit complement, but not by human complement. Analysis of membrane complement regulatory proteins (mCRP) on breast carcinoma cells revealed a heterogenous expression of CD46, CD55 and CD59. After blocking the mCRP activity with specific antibodies, rhumAb anti-HER2 induced about 15% lysis of p185HER2-expressing tumor cells. Tumor cell sensitization with rabbit polyclonal anti-tumor antiserum following mCRP neutralization, augmented cell lysis from 10 to 80%. Expression of mCRP was upregulated by treatment with PMA, and correlated with increased protection of the tumor cells from complement lysis. These results suggest that humanized antibodies like rhumAb anti-HER2 promote complement activation leading to tumor cell phagocytosis and cell-mediated cytotoxicity. They further demonstrate that a successful tumor immunotherapeutical approach, based on antibody and complement treatment, requires mCRP neutralization.

C1 inhibitor in anti-inflammatory therapy: from animal experiment to clinical application

Potentially life-threatening consequences due to severe inflammatory tissue destruction are often closely associated with an excessive activation of the complement system. Various clinical disorders, including capillary leak syndrome, septic shock, multiple organ failure and hyperacute graft rejection are at least in part driven by an overactivated complement system. Therapeutic support of complement regulation appears to be a logical approach to reduce undesirable inflammatory reactions. C1 inhibitor, a multifunctional regulator of all major kinin-generating protein cascade systems, is frequently observed to be reduced in patients suffering from severe inflammation, due to ligand-induced inactivation of the regulatory protein. After C1 inhibitor has for many years been proven beneficial in acute treatment of hereditary angioedema, a growing number of reports now suggests that C1 inhibitor provides an effective means to protect against complement-mediated inflammatory tissue damage. These studies not only include pathophysiologically relevant animal models but also first attempts to prove the benefits of C1 inhibitor as a novel therapeutic approach in clinical trials.

Mouse-to-rabbit xenotransplantation: a new small animal model of hyperacute rejection mediated by the classical complement pathway

BACKGROUND

Hyperacute rejection of porcine organs transplanted into primate recipients is initiated by the binding of preformed xenoreactive natural antibodies to the vascular endothelium of the graft and activation of the classical complement pathway. Several small animal models are currently employed to study various aspects of xenograft rejection; however, none has been shown to manifest hyperacute rejection mediated by the classical pathway of complement activation.

METHODS

We performed heterotopic mouse heart transplants into weanling rabbits, adult rabbits, and C6-deficient rabbits. The recipients received no immunosuppression. Rejected grafts were subjected to histologic analysis and immunofluorescence staining for rabbit IgG, IgM, and C3. Levels of preexisting cytotoxic antibodies as well as classical and alternative complement pathway activities were determined in rabbit serum using mouse red cells as targets.

RESULTS

Mean graft survival was 37+/-9.6 min for mouse-to-weanling rabbit transplants (n=10), and 40+/-11.1 min for mouse-to-adult rabbit transplants (n=5). Rejected grafts showed diffuse interstitial hemorrhage, endothelial cell damage, myocyte necrosis, moderate diffuse deposition of rabbit IgG, and dense deposition of rabbit IgM and C3 on the vascular endothelium of the graft, consistent with hyperacute rejection. One mouse-to-C6-deficient rabbit transplant was rejected at 21 hr with severe interstitial hemorrhage, cellular necrosis and a moderate cellular infiltrate consisting primarily of neutrophils and some mononuclear cells. A second transplant in a C6-deficient rabbit was functioning when the recipient died at 6.5 hr as a result of complications of surgery; the graft had normal myocytes and vasculature with minimal spotty interstitial hemorrhage. Both weanling and adult rabbit serum were found to have high titers of cytotoxic IgM anti-mouse antibodies and strong classical complement pathway activity with minimal alternative pathway activity towards mouse red cells.

CONCLUSIONS

The mouse-to-rabbit species combination manifests hyperacute xenograft rejection. In vitro studies suggest that this process is mediated by IgM anti-mouse natural antibodies and activation of the classical pathway of complement.

Complement inhibition by soluble complement receptor type 1 improves microcirculation after rat liver transplantation

BACKGROUND

Recent observations provide evidence that complement is involved in the pathophysiology of ischemia/reperfusion injury. In this study, we assessed the impact of complement inhibition on hepatic microcirculation and graft function using a rat model of liver transplantation.

METHODS

Arterialized orthotopic liver transplantation was performed in Lewis rats after cold preservation (University of Wisconsin solution, 4 degrees C, 24 h). Eight animals received the physiological complement regulator soluble complement receptor type 1 (sCR1) intravenously 1 min before reperfusion. Controls received Ringer's solution (n=8). Microvascular perfusion, leukocyte adhesion, and Kupffer cell phagocytic activity were studied 30-100 min after reperfusion by in vivo microscopy.

RESULTS

Microvascular perfusion in hepatic sinusoids was improved in the sCR1 group (87+/-0.7% vs. 50+/-1%; P < 0.001). The number of adherent leukocytes was reduced in sinusoids (68.3+/-4.7 vs. 334.1+/-15.8 [adherent leukocytes per mm < or = liver surface]; P < 0.001) and in postsinusoidal venules after sCR1 treatment (306.6+/-21.8 vs. 931.6+/-55.9 [adherent leukocytes per mm < or = endothelial surface]; P < 0.001). Kupffer cell phagocytic activity was decreased in the sCR1 group compared to controls. Postischemic bile production reflecting hepatocellular function was increased by almost 200% (P = 0.004) after complement inhibition. Plasmatic liver enzyme activity was decreased significantly upon sCR1 treatment, indicating reduced parenchymal cell injury.

CONCLUSIONS

Our results provide further evidence that the complement system plays a decisive role in hepatic ischemia/reperfusion injury. We conclude that complement inhibition by sCR1 represents an effective treatment to prevent reperfusion injury in liver transplantation.

[Significance of the complement system for xenotransplantation: strategies for therapeutic intervention]

Hyperacute graft rejection triggered by the activation of the recipient's complement system represents the major obstacle to successful xenotransplantation. After the binding of preformed antibodies to vascular glycoproteins complement-induced activation and injury of endothelial cells with subsequent thrombosis leads to rapid destruction of foreign tissues. Inhibition of complement activation is therefore considered as a prerequisite for xenograft survival. Recent animal and cell culture experiments suggest that support of the physiological regulation of the complement system appears to be most promising. Besides the application of soluble complement inhibitors (e.g. soluble complement receptor 1, sCR1; C1 inhibitor) the genetic transfer of human membrane-bound complement regulatory proteins (e.g. DAF, CD59) offers new chances to protect the xenograft against the cytolytic complement attack. Results from the authors' experiments shall be included in a short overview to the issue.

SC5b-9 is the most sensitive marker in assessing disease activity in Brazilian SLE patients

This study investigated whether increased plasma levels of terminal complement complex (SC5b-9) or split products correlate with disease activity and clinical manifestations in Brazilian systemic lupus erythematosus (SLE) patients. Comparisons with conventional measurements of complement and other inflammatory markers were also performed. Plasma levels of SC5b-9, C3a desArg, C1rs-C1Inhibitor, C3b(Bb)P, C3, C4, erythrocyte sedimentation rate (ESR) and mucoproteins (MP) were measured in 41 patients with SLE of different disease activity: 10 patients with none, 15 patients with mild, and 16 patients with moderate or severe activity. All parameters, with the exception of C3 and C3b(Bb)P, showed a statistically significant correlation with disease activity. Plasma levels of SC5b-9, C3a desArg, C4, CH50, ESR and MP revealed significant differences between the groups of patients without activity and those with moderate or severe disease. Although none of the variables were able to discriminate between patients without and those with mild activity, SC5b-9, C3a desArg, C4, ESR and mucoproteins showed significant differences between the patients with mild and those with moderate or severe disease. Among all the variables, SC5b-9 levels showed the most significant results and correlated well with the severity of the disease (p < 0.0005). Our data suggest that elevated levels of complement activation products, particularly of SC5b-9 are more sensitive markers in assessing disease activity than conventional laboratory diagnosis. Modern complement diagnosis is therefore recommended for monitoring disease progress in SLE patients.

White blood cell counts and plasma C3a have synergistic predictive value in patients at risk for acute respiratory distress syndrome

OBJECTIVE

To investigate and select nonassociated variables with predictive value for acute respiratory distress syndrome (ARDS) in patients at risk.

DESIGN

Prospective, observational study.

SETTING

A university hospital intensive care unit.

PATIENTS

Twenty-four critically ill patients with different risk factors for ARDS.

INTERVENTIONS

Arterial and mixed venous blood, as well as urine samples, were collected. Invasive hemodynamic measurements were performed.

MEASUREMENTS AND MAIN RESULTS

Fifty-nine variables pertaining to the cardiorespiratory, hepatic, immunologic, and renal systems and including plasma complement activation products C3a and SC5b-9 and polymorphonuclear elastase, were determined every 6 hrs for 3 days in patients at risk for ARDS. Associations among variables were investigated and the predictive value of nonassociated variables for ARDS was determined. Patients who developed ARDS (n=8) had lower white blood cell counts at the time they entered the study (p=.006) and during the first 24 hrs thereafter (p=.032). Also, plasma C3a concentrations were markedly higher during the first 24 hrs in patients who developed ARDS (p=.006). Plasma C3a had better predictive value than did white blood cell counts for cutoff points set by discriminant analysis at 1075 ng/mL (1.075 x 10(-3) g/L) and 5700 cells/mL, respectively. The combination of both variables in a discriminant function improved the predictive value for ARDS.

CONCLUSIONS

The most notable and nonassociated alterations observed in patients who developed ARDS were lower white blood cell counts and higher plasma C3a concentrations compared with counts and concentrations in patients who did not develop ARDS. Plasma C3a concentrations showed better predictive value than white blood cell counts. The combination of white blood cell counts with plasma C3a concentrations synergistically improved the predictive value for ARDS. This combination may prove useful for identifying subpopulations at highest risk for ARDS and may contribute to make treatment at an early stage of the syndrome possible.

Activated autologous blood therapy in recurrent spontaneous abortion--results of a pilot study

This study was undertaken to investigate the influence of activated autologous blood therapy on immunological parameters and on the clinical outcome in patients with recurrent spontaneous abortion. In a prospective trial, 36 women with recurrent spontaneous abortion were treated with intramuscular reinjections of extracorporally haemolysed and ultraviolet irradiated autologous blood. A comprehensive immunological investigation revealed significant changes in lymphocyte subpopulations, plasma complement levels, mitogen stimulation and immunoglobulin levels during the treatment period. No side-effects were reported by the patients. From June 1994 to November 1995, 22 intrauterine and one extrauterine pregnancies occurred, resulting in 19 (86%) live births, two (9%) spontaneous abortions and one (4%) artificial abortion compared with a 64% live birth rate in the historical control group. We conclude that activated autologous blood therapy has detectable effects on the immune system, and seems to be promising for further investigation concerning the treatment of idiopathic recurrent spontaneous abortion.

[Hereditary angioedema: clinical and laboratory aspects of 7 cases]

Hereditary angioedema is caused by a defect in C1 inhibitor activity (C1INH). Its occurrence is rare and it is associated with an autosomal dominant mode of inheritance. We describe seven patients (4M:3F), age from 12 to 50 years old, who are affected by hereditary angioedema; four of them belong to the same family. The main clinical manifestations were: angioedema of face, hands and feet (6/7) and abdominal pain (2/7). No triggering factors were associated with symptoms in 4/7 patients and trauma (2/7) and menses (1/7) were reported in the other three ones. One patient was submitted to laparotomy for partial intestinal resection, before diagnosis. Laboratory complement analysis revealed the absence of hemolytic function of complement, reduced C4 (6/7) and low C1INH levels. All patients received Danazol (100 mg/day) with clinical control. Hereditary angioedema has to be considered in the differential diagnosis of angioedema, since an early diagnosis of this immunodeficiency, leading to specific treatment in order to decrease the complications.

Complement factor I deficiency in a family with recurrent infections

Factor I deficiency causes a permanent, uncontrolled activation of the alternative pathway resulting in an increased turnover of C3 and consumption of factor B, factor H and properdin. Factor I deficiency is clinically associated with recurrent bacterial infections already in early infancy, mainly affecting the upper and lower respiratory tract, or presenting as meningitis or septicemia. We here report on a Brazilian family (n = 9) with known consanguinity, where in 3/7 children, suffering from chronic otitis, meningitis, and respiratory infections, a complete factor I deficiency was recognized. One of the patients died after fulminant sepsis. Hemolytic activity of the alternative pathway was not detectable in the patients' sera due to decreased plasma concentrations of C3, factor B and properdin. As a consequence of factor I deficiency, C3b could not be metabolized with the result that no C3-derived split products (C3dg/C3d) were detectable in the patients' sera. In vitro reconstitution with purified factor I restored the regulatory function in the patients' sera with the subsequent cleavage of C3b to C3c and C3dg. Factor H levels were decreased in all patients' sera and found to be tightly complexed with C3b resulting in a modified electrophoretic mobility. Upon factor I reconstitution, factor H was released from C3b regaining its beta 1 electrophoretic mobility. Complement-mediated biological functions like opsonization of bacteria, chemotactic activity and phagocytosis in these patients were impaired. The parents (cousins, 2nd degree) and 3/4 siblings had significantly reduced factor I plasma levels without further alteration in their complement profile. 3 of these obviously heterozygously deficient family members suffered from recurrent bacterial infections of different frequency and severity.

Molecular, genetic, and functional analysis of homozygous C8 beta-chain deficiency in two siblings

C8 deficiency is associated with an increased susceptibility to neisserial infections. We present a case of an 11 year old boy who suffered from infection with Neisseria meningitidis. Medical history of the patient and his family (n = 5) did not indicate any previous immunodeficiency symptoms. Results from the analysis of phagocyte and lymphocyte functions were within the normal range. No hemolytic activities of the classical (CH50) and the alternative (APH50) pathways of complement were measurable, and SC5b-9 protein complexes could not be detected in the patient's plasma. Further analysis by highly sensitive ELISA and functional assays revealed a complete deficiency of C8. Upon the reconstitution with purified C8 total hemolytic activity could be restored. SDS-PAGE and Western blot analysis established a deficiency of the C8 beta chain. Genetic analysis at the genomic DNA level demonstrated the common C-T mutation in exon 9 of the C8B gene. Family analysis presented the older sister with non-detectable function of C8 in serum, both parents with about half-normal C8 titres, and the younger sister with normal C8 function. The parents and both sisters were asymptomatic, although the older of the sisters presented with the same complete C8 beta-chain deficiency as the patient described.

IN CONCLUSION

the common C-T mutation in the C8B genes is the genetic basis of C8 beta-chain deficiency in two members of this Bosnian family.

Controlling the complement system in inflammation

Inappropriate or excessive activation of the complement system can lead to harmful, potentially life-threatening consequences due to severe inflammatory tissue destruction. These consequences are clinically manifested in various disorders, including septic shock, multiple organ failure and hyperacute graft rejection. Genetic complement deficiencies or complement depletion have been proven to be beneficial in reducing tissue injury in a number of animal models of severe complement-dependent inflammation. It is therefore believed that therapeutic inhibition of complement is likely to arrest the process of certain diseases. Attempts to efficiently inhibit complement include the application of endogenous soluble complement inhibitors (C1-inhibitor, recombinant soluble complement receptor 1- rsCR1), the administration of antibodies, either blocking key proteins of the cascade reaction (e.g. C3, C5), neutralizing the action of the complement-derived anaphylatoxin C5a, or interfering with complement receptor 3 (CR3, CD18/11b)-mediated adhesion of inflammatory cells to the vascular endothelium. In addition, incorporation of membrane-bound complement regulators (DAF-CD55, MCP-CD46, CD59) has become possible by transfection of the correspondent cDNA into xenogeneic cells. Thereby, protection against complement-mediated inflammatory tissue damage could be achieved in various animal models of sepsis, myocardial as well as intestinal ischemia/reperfusion injury, adult respiratory distress syndrome, nephritis and graft rejection. Supported by results from first clinical trials, complement inhibition appears to be a suitable therapeutic approach to control inflammation. Current strategies to specifically inhibit complement in inflammation have been discussed at a recent meeting on the 'Immune Consequences of Trauma, Shock and Sepsis', held from March 4-8, 1997, in Munich, Germany. The Congress (chairman: E. Faist, Munich, Germany), which was held in close cooperation with various national and international shock and trauma societies, was attended by about 2000 delegates from 40 countries. The major objective of the meeting was to provide an overview on the most state-of-the-art methods to prevent multiple organ dysfunction syndrome (MODS)/multiple organ failure (MOF) following the systemic inflammatory response (SIRS) to severe trauma. One of the largest symposia held within the Congress was devoted to current aspects of controlling complement in inflammation (for abstracts see: Shock 1997, 7 Suppl., 71-75). After providing the audience with information on the scientific background by addressing the clinical relevance of complement activation (G.O. Till, Ann Arbor, MI, USA) and discussing recent developments in modern complement diagnosis (J. Köhl, Hannover, Germany), B.P. Morgan (Cardiff, UK) introduced the symposium's special issue by giving an overview on complement regulatory molecules. Selected topics included overviews on the application of C1 inhibitor (C.E. Hack, Amsterdam, NL), sCR1 (U.S. Ryan, Needham, MA, USA), antibodies to C5 (Y. Wang, New Haven CT, USA) and to the anaphylatoxin C5a (M. Oppermann, Göttingen, Germany), and a report on complement inhibition in cardiopulmonary bypass (T.E. Mollnes, Bodø, Norway). The growing interest of clinicians in complement-directed anti-inflammatory therapy, and the fact that only some of the various aspects of therapeutic complement inhibition could be addressed on the meeting, has motivated the author to expand a Congress report into a short comprehensive review on recent strategies to control complement in inflammation.

Brazilian report on primary immunodeficiencies in children: 166 cases studied over a follow-up time of 15 years

One hundred sixty-six cases of primary immunodeficiency diseases (PID) (95 males, 71 females), diagnosed according to WHO criteria, have been registered at the Children's Hospital, University of São Paulo, Brazil. The following frequencies were found: predominantly humoral defects, 60.8% (n = 101); T cell defects, 4.9% (n = 8); combined ID, 9.6% (n = 16); phagocyte disorders, 18.7% (n = 31); and complement deficiencies, 6% (n = 10). IgA deficiency was the most frequent disorder (n = 60), followed by transient hypogammaglobulinemia (n = 14), chronic granulomatous disease (n = 14), and X-linked agammaglobulinemia (n = 9). In comparison to other (national) reports, we observed higher relative frequencies of phagocyte and complement deficiencies. Recurrent infections were the cause of death in 12.7%. Allergic symptoms were observed in 41%, mainly in IgA-deficient, hypogammaglobulinemic, or hyper-IgE patients, and autoimmune disorders in 5%, predominantly in IgA and complement deficiencies. Five patients suffered from BCG dissemination; two of them died. This is the first Brazilian report on PID over an observation time of 15 years.

Inverse correlation between IgG-antihinge region and antierythrocyte autoantibody in chronic benign and malignant cold agglutination

Previous reports provided evidence of an immunosuppressive role of natural anti-F(ab')2 antibodies. If suppressive anti-F(ab')2 antibodies also regulated the autoantibody production in cold agglutination, one would expect high titers of anti-F(ab')2 to be associated with low titers of cold agglutinins. Indeed, our previous studies revealed an inverse correlation between IgG-anti-F(ab')2 and cold agglutinins. Many previous experiments focused on anti-F(ab')2 of an antiidiotypic nature. Recent epitope mapping showed that anti-F(ab')2 of healthy persons is not an antiidiotype but recognizes a hinge region sequence. We attempted to answer the question whether this IgG-antihinge antibody is responsible for the previously described association between anti-F(ab')2 and cold agglutinins. IgG-antihinge and IgG-anti-F(ab')2 antibody was determined and statistically analyzed in the serum of 334 patients with cold agglutination. Our experiments revealed a strong correlation between the concentrations of antihinge and the previously described anti-F(ab')2 antibody. The anti-F(ab')2 activity was competitively inhibited by a synthetic hinge peptide. Moreover, patients with high antihinge titers had low cold agglutinin titers, and vice versa. A stratification according to cold agglutinin specificity and disease etiology showed that the inverse correlation is present only in anti-I and anti-i patients suffering from monoclonal B-lymphocyte proliferation. In conclusion, our results confirm the correlation previously described for anti-F(ab')2 antibody and antierythrocyte autoantibody and define for the first time an association between an idiotype-independent anti-IgG autoantibody and cold agglutinin.

Comparative study of the complement-activating and specific IgE-binding properties of ragweed pollen allergen

Previous reports have defined the capacity of ragweed pollen extract (RWA) to activate human complement (C) in fluid phase through the classical pathway and have ascertained a strong correlation between the extent of complement activation and the severity of symptoms of allergic rhinoconjunctivitis during the ragweed blooming season. In the present study the complement-activating and specific IgE-binding capacities of various ragweed allergen preparations were compared. Elimination of physically adsorbed (flavonoid) pigments from the allergenic proteins had no significant effect on their complement-consuming capacity, although the process strongly diminished specific IgE binding. Removal of an IgE-binding trypsin inhibitor from RWA significantly enhanced RWA-induced complement activation, whereas it did not change IgE binding. These findings indicate that neither the physically adsorbed pigments nor the trypsin inhibitor are involved in complement activation by ragweed pollen allergens, and suggest that complement activation and specific IgE binding are distinct molecular properties of ragweed pollen allergen.

Secreted chondroitin sulfate proteoglycan of human B cell lines binds to the complement protein C1q and inhibits complex formation of C1

We recently characterized a species of proteochondroitin sulfate (CSPG) secreted by human B cell lines that closely resembles in its structure the serum-derived C1q inhibitor (C1qI). These proteoglycans have in common a molecular mass of approximately 130 to 150 kDa with a core protein of 30 kDa to which up to four chondroitin sulfate chains each of approximately 26 kDa are attached. Since this B cell-derived CSPG is a potential source for serum C1qI, we measured its capacity to interact with C1q in solid-phase binding and complex electrophoresis assays. B cell CSPG purified from culture supernatants of the two human B cell lines JOK-1 and U266 strongly bound to C1q. In contrast to the secreted form, cellular proteoglycan of the myeloma cell line U266 did not interact with C1q. Binding of C1q to CSPG was competitively inhibited by free glycosaminoglycans (GAG) in the order dextran sulfate > heparin > heparan sulfate > chondroitin-6-sulfate (CS-C) > dermatan sulfate (CS-B) > chondroitin-4-sulfate (CS-A). B cell CSPG inhibited the hemolytic activity of C1q and C1. In addition, B cell CSPG blocked C1q receptor binding in a dose-dependent manner. The proteoglycans did not influence the activity of C1 complex already bound to EAC4 target cells. By interaction of CSPG with solid-phase-bound C1q, formation of the C1 complex upon the addition of C1r and C1s was impaired. Strong binding of B cell CSPG to C1q, its inhibition of C1q activity, and its structural similarities to the previously described human serum C1qI indicate that B cells produce a soluble CSPG, which may act as C1qI under physiologic conditions.

Secreted chondroitin sulfate proteoglycan of human B cell lines binds to the complement protein C1q and inhibits complex formation of C1

We recently characterized a species of proteochondroitin sulfate (CSPG) secreted by human B cell lines that closely resembles in its structure the serum-derived C1q inhibitor (C1qI). These proteoglycans have in common a molecular mass of approximately 130 to 150 kDa with a core protein of 30 kDa to which up to four chondroitin sulfate chains each of approximately 26 kDa are attached. Since this B cell-derived CSPG is a potential source for serum C1qI, we measured its capacity to interact with C1q in solid-phase binding and complex electrophoresis assays. B cell CSPG purified from culture supernatants of the two human B cell lines JOK-1 and U266 strongly bound to C1q. In contrast to the secreted form, cellular proteoglycan of the myeloma cell line U266 did not interact with C1q. Binding of C1q to CSPG was competitively inhibited by free glycosaminoglycans (GAG) in the order dextran sulfate &gt; heparin &gt; heparan sulfate &gt; chondroitin-6-sulfate (CS-C) &gt; dermatan sulfate (CS-B) &gt; chondroitin-4-sulfate (CS-A). B cell CSPG inhibited the hemolytic activity of C1q and C1. In addition, B cell CSPG blocked C1q receptor binding in a dose-dependent manner. The proteoglycans did not influence the activity of C1 complex already bound to EAC4 target cells. By interaction of CSPG with solid-phase-bound C1q, formation of the C1 complex upon the addition of C1r and C1s was impaired. Strong binding of B cell CSPG to C1q, its inhibition of C1q activity, and its structural similarities to the previously described human serum C1qI indicate that B cells produce a soluble CSPG, which may act as C1qI under physiologic conditions.

Protection of porcine endothelial cells from complement-mediated cytotoxicity by the human complement regulators CD59, C1 inhibitor, and soluble complement receptor type 1. Analysis in a pig-to-human in vitro model relevant to hyperacute xenograft rejection

Inhibition of complement activation is considered a prerequisite to overcome hyperacute xenograft rejection. In the present study, we investigated the efficacy of C1 inhibitor (C1 inh) and recombinant soluble complement receptor type 1 (rsCR1) to protect xenogeneic cells against complement-mediated cytotoxicity in an in vitro xenotransplantation model. The addition of the soluble complement regulators to human serum led to a dose-dependent inhibition of complement-mediated destruction of aortic porcine endothelial cells (PEC). On a molar base, rsCR1 was more efficient than C1 inh. Transfection of PEC with cDNA of human CD59 resulted in several clones where protection against complement-mediated cell destruction correlated with the expression level of the inhibitor. Addition of low concentrations of C1 inh and rsCR1 to a CD59 (human)-positive PEC clone, expressing a suboptimal level of the membrane-bound regulator, resulted in a significant improvement of protection against complement-mediated cell destruction.

Dialysis in rats with acute renal failure: evaluation of three different dialyzer membranes

Exposure to complement-activating cellulosic dialysis membranes has been claimed to adversely affect the course of acute renal failure (ARF). To test this hypothesis, male Sprague-Dawley rats were allocated to 2 groups: in Group 1, ARF was induced by bilateral renal artery clamping whereas in Group 2, animals underwent a sham procedure. In each group, rats were further allocated to undergo hemodialysis with either a Cuprophan, a Hemophan, or a polyacrylonitrile minidialyzer on Days 4 and 8 after surgery, or no dialysis. Renal function was measured by inulin clearance on the days after dialysis. Additionally, total complement activity (CH50) was estimated on Days 1, 2, 4, and 8, and complement factor C3 was detected immunohistochemically. The degree of renal failure and the rate of recovery of renal function were similar in all the ARF groups irrespective of whether they had undergone dialysis or not, or of the type of the dialysis membrane. Furthermore, there were no significant differences in the course of CH50 or in the amount and distribution of complement factor C3 in the kidney tissue between the rats of Groups 1 and 2. Our findings refute the hypothesis that in ischemic ARF exposure to complement-activating cellulosic dialysis membranes impairs the recovery of renal function in rats.

[Effect of complement modulation with the soluble complement receptor sCR1 on survival and function of kidney xenotransplant. An experimental study with a new guinea pig to rate transplant model]

In this study a modified experimental kidney xenograft model was developed, which reproduced, in a reliable way, the course of hyperacute rejection. In this model guinea-pig kidneys were transplanted to rats using end-to-side anastomoses with recipient aorta and vena cava, respectively, and ureter drainage for diuresis monitoring. The aim of this study was to investigate the protective effects of complement modulation by soluble complement receptor 1 (sCR1) on the xenografts. Twenty-four xenotransplantations were performed and recipients randomized for treatment either by 3 ml saline or 50 mg/kg sCR1 as a 3-ml bolus. It was found that sCR1 was highly efficient in delaying hyperacute rejection from 10.5 +/- 2.1 min in the control group to at least 2 h in the therapy group and in prolongation of graft function. The complement activity was significantly reduced in the sCR1-treated rats, even at the time of rejection, as a result of complement modulation in this group of xenograft recipients. Xenografts from saline-treated animals showed necroses, interstitial haemorrhages and platelet aggregates occluding the vessels as soon as 10 min after the reperfusion started. No such changes could be seen even after 120 min in the xenografted kidneys of sCR1-treated rats. Also C3 deposits in the glomeruli and interstitium were markedly reduced.