The cytolytically inactive terminal complement complex activates endothelial cells to express adhesion molecules and tissue factor procoagulant activity.

The membrane attack complex of complement (C) in sublytic concentrations stimulates endothelial cells (EC) to express adhesion molecules and to release biologically active products. We have examined the ability of a cytolytically inactive form of this complex, which is incapable of inserting into the cell membrane, to upregulate the expression of adhesion molecules and of tissue factor (TF) procoagulant activity. The inactive terminal C complex (iTCC) was prepared by mixing C5b6, C7, C8, and C9 and was purified by fast protein liquid chromatography on a Superose 12 column. Binding of this complex to EC was found to be dose dependent and was inhibited by anti-C9 antibodies, as assessed both by ELISA using an mAb anti-C9 neoantigen and by measuring cell-bound 125I-labeled iTCC. Exposure of EC to iTCC resulted in a dose- and time-dependent expression of endothelial leukocyte adhesion molecule 1, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1 accompanied by increased levels of the corresponding mRNA, but not in the rapid expression of P-selectin. Inactive TCC also induced increased TF activity evaluated by a chromogenic assay that measures the formation of factor Xa. These effects were inhibited by anti-C9 antibodies. The data support the conclusion that iTCC may induce proinflammatory and procoagulant activities on EC.

Hepatocyte nuclear factor 1alpha controls the expression of terminal complement genes.

The terminal components of the complement system contribute to host defense by forming the multiprotein membrane attack complex (MAC) which is responsible for cell lysis and several noncytotoxic effects. Most of the complement proteins are synthesized in the liver, but the mechanisms controlling their tissue-specific expression have not been elucidated. In this study we show that mice lacking the hepatic transcription factor hepatocyte nuclear factor 1alpha (HNF1alpha) fail to transcribe C5 and C8A complement genes. In addition, mRNAs encoding for several other terminal complement components or subunits are expressed at lower levels, including C8beta, C8gamma, and C9. We next used a reconstitution assay involving human sera with selective complement deficiencies to assess mouse complement activity. Sera from HNF1alpha-deficient mice showed negligible hemolytic activity of both C5 and C8alpha-gamma subunits. The activity of C8beta was severely affected despite only a 50% reduction in C8beta mRNA levels in the liver. This is reminiscent of C8alpha-gamma-deficient patients who accumulate extremely low levels of the C8beta subunit. Our results demonstrate that HNF1alpha plays a key role in the expression of C5 and C8A genes, two terminal complement component genes that are essential for the assembly of MAC as a result of complement activation.

Complement-endothelial cell interactions: pathophysiological implications.

The function of the endothelial cells can be modulated by humoral factors present in the circulation and in the extravascular fluid, including proteins of the complement system. This review examines the multiple interactions between the complement system and the endothelial cells and their functional consequences on inflammation, coagulation and regulation of vascular tone. The implications of these interactions in the induction and progression of the vascular lesions occurring in atherosclerosis, ischemia/reperfusion and xenotransplantation and the possible therapeutic approaches in terms of complement regulation are also discussed.

Peritoneal mesothelial cells produce complement factors and express CD59 that inhibits C5b-9-mediated cell lysis.

The CD59 membrane protein confers protection from C5b-9-mediated cell lysis. Because evidence exists for complement (C) activation and generation of C5b-9 in the peritoneal cavity during chronic peritoneal dialysis (CPD), we investigated, on mesothelial cell (MC) lines, the expression of CD59 and the production of C components. Four MC lines were obtained from children on CPD, and two from non uremic children. CD59 expression on MCs was investigated with anti-CD59 monoclonal antibody (mAb) and polyclonal goat immunoglobulin G (IgG). MC lines were positive for staining with anti-CD59 mAb. Western blotting analysis of MC membrane demonstrated a band with the same molecular weight as CD59. Incubation of MC with anti-CD59 mAb abrogated the protective effect of CD59 (100% cytotoxicity). C3, C4, and C6 were detected in the supernatants of MC; in non uremic MC supernatants, C5, C7, C8, and C9 were also detectable, and C4 concentration was tenfold higher. CD59 expression confers to MCs protection from C5b-9-mediated lysis. MCs produce C factors. These findings suggest that production of complement components and expression of CD59 on MCs could play a role both in peritoneal cavity infection (decreased complement production) and in peritoneal membrane damage (decreased CD59 expression and reduced remesothelialization owing to MC lysis).

[The maternal-fetal immune relationship in pregnancy]. / Il rapporto immune materno-fetale in gravidanza.

The mother establishes with the fetus a special interaction in pregnancy allowing his normal survival in spite of the different HLA antigens. The main factors contributing to these favourable conditions for the fetus are an efficient local immunosuppression and the formation of a protective barrier between the mother and the fetus. A number of substances are responsible for the local immunosuppression and include cytokines, prostaglandins, hormones as well as various other proteins of pregnancy. In addition, cytokines produced by TH2 lymphocytes seem to be predominant with respect to those of TH1 cells. An effective protection is provided by the trophoblast layer, which not only forms a physical barrier between the mother and the fetus but evades the immune attack of the mother by expressing inhibitory molecules of the complement system and by down regulating the expression of HLA antigens. Data obtained from murine models and clinical observation in pathological pregnancies suggest that an abnormal immune response of the mother against the feto-placental unit may be responsible for the occurrence of recurrent spontaneous abortions. This is proved by the ability of the partner's lymphocytes administered to females in the mouse model prior to mating to reduce the incidence of abortions. Unfortunately, similar treatment in women with recurrent abortion does not appear to be very effective.

The endothelium is an extrahepatic site of synthesis of the seventh component of the complement system.

The level of the terminal complement components secreted by human umbilical vein endothelial cells (HUVEC) was measured by a sensitive ELISA which allows the detection of 30-50 pg/ml of these components. C7 was the only terminal component detected in measurable amounts in the cell supernatant. The mean value was 11 ng/106 cells at 96 h and was slightly higher than that of C3 (9 ng/106 cells). HUVEC and serum C7 analysed by SDS-PAGE and immunoblot exhibited the same electrophoretic mobility. A proportion of C7 secreted by HUVEC was incorporated into the terminal complement complex (TCC) assembled spontaneously in the supernatant of cells cultured in C7-deficient human serum, and was not detected by the standard ELISA for C7 measurement. By adding the amount of C7 present in the TCC to that of free C7, the total amount of the component released by HUVEC was calculated to be approximately 35 ng/106 cells. Further TCC was produced following complement activation of the cell supernatant through the alternative pathway. Synthesis of C7 by HUVEC was confirmed by inhibition experiments in the presence of cycloheximide and by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of C7 mRNA expression. Addition of IL-1alpha and tumour necrosis factor-alpha to the cell culture stimulated the secretion of C3, but had no effect on the synthesis of C7. By contrast, interferon-gamma had only a marginal effect on the production of C3, but markedly down-regulated the synthesis of C7 as assessed both by ELISA and RT-PCR.

Characterization of soluble terminal complement complex assembled in C8beta-deficient plasma and serum.

Sera genetically deficient in either the alpha-gamma or the beta-subunit of complement component C8 virtually lack haemolytic activity. We have studied the formation and the structural organization of the soluble terminal complement complex (TCC) assembled in these sera following activation with cobra venom factor (CVF). The TCC concentration in the activated C8alpha-gamma and C8beta-deficient samples was 0.2% and 4%, respectively, when compared with zymosan-activated normal serum. TCC was purified from the activated C8beta-deficient samples by affinity chromatography and analysed by immunoblotting and enzyme immunoassay. No C8beta was detected in one TCC preparation, while 7% of the normal level was present in the other. The level of the other terminal components, including that of C8alpha-gamma, was normal. The ability of C8alpha-gamma to promote the assembly of TCC in the presence of a limited amount of C8beta or in the apparent absence of this subunit was confirmed using purified components, by mixing C5b6 and either of the purified C8 subunits together with C7 and C9. These data show that soluble TCC can be formed in C8beta-deficient sera that contain little or no C8beta.

Prevalence and biological effects of anti-trophoblast and anti-endothelial cell antibodies in patients with recurrent spontaneous abortions.

PROBLEM: Trophoblasts and endothelial cells represent a potential target for antibodies in women with recurrent spontaneous abortions. These antibodies have been shown to be associated with anti-phospholipid antibodies. Are they also present in women with unexplained pregnancy losses in the absence of anti-phospholipid antibodies? METHOD OF STUDY: The anti-trophoblast antibodies were tested by an immunofluorescence assay on cells purified from pooled first-trimester placentae, whereas the anti-endothelial cell antibodies were measured by enzyme-linked immunoadsorbent assay (ELISA) on cells isolated from the umbilical vein and were cultured to confluence. The cytotoxicity of trophoblasts was evaluated in a homologous system. The expression of adhesion molecules on endothelial cells was quantitated by ELISA using specific monoclonal antibodies, and the expression of tissue factor was quantitated by a chromogenic assay measuring the formation of factor Xa. RESULTS AND CONCLUSIONS: Complement-fixing antibodies to trophoblast represent a better marker to discriminate patients with recurrent spontaneous abortions from controls and are cytotoxic for the target cells. Anti-endothelial antibodies are also present in these patients and exhibit pro-inflammatory and pro-coagulant activities.

Inhibition of trophoblast adhesion to endothelial cells by the sera of women with recurrent spontaneous abortions.

PROBLEM: May anti-phospholipid or other autoantibodies interfere with trophoblast-endothelial cells interaction in women with unexplained pregnancy losses? METHODS OF STUDY: The sera of 72 women with recurrent spontaneous abortions (RSA) containing antibodies to endothelial cells (28), trophoblast (14), and cardiolipin (10) or lacking antibodies (25), and 26 controls were examined in an inhibition assay of trophoblast adhesion to endothelial cells using an ELISA based on the recognition of trophoblast by antibodies to cytokeratin. RESULTS: Adhesion of trophoblast to endothelial cells was time- and dose-dependent. Patients and control sera inhibited trophoblast adhesion with mean values of 37% and 7%, respectively. Inhibition above 2SD of the mean control value was still observed in 58% of the patients sera and 8% of the control sera. Sera containing antibodies to endothelial cells had higher inhibitory effect (38%) than those with antibodies to trophoblast (23%) and cardiolipin (28%) or lacking antibodies (26%). CONCLUSIONS: Antibodies and other undefined factors in the sera of women with RSA inhibit adhesion of trophoblast to endothelial cells.

Complement-fixing islet cell antibodies in type-1 diabetes can trigger the assembly of the terminal complement complex on human islet cells and are potentially cytotoxic.

Forty-one sera of patients with IDDM (insulin-dependent diabetes mellitus) containing complement-fixing islet cell antibodies were analyzed for their ability to activate TCC (terminal complement complex). Eighteen sera were found to promote deposition of TCC on human islets of pancreatic cryostat sections with a nonhomogeneous pattern of distribution corresponding to that of insulin. Activation of TCC by IDDM serum and binding of this complex to islet cells was confirmed using purified islets. Flow cytometric analysis of islet cell treated with a TCC+ IDDM serum showed IgG binding to the cell surface. The same serum had a cytotoxic effect on islet cells in the presence of human C. These results obtained with a homologous system of C activation by IDDM sera suggest that TCC may contribute, at least in part, to the pancreatic beta cell damage.

Multimer formation and ligand recognition by the long pentraxin PTX3. Similarities and differences with the short pentraxins C-reactive protein and serum amyloid P component.

PTX3 is a prototypic long pentraxin consisting of a C-terminal 203-amino acid pentraxin-like domain coupled with an N-terminal 178-amino acid unrelated portion. The present study was designed to characterize the structure and ligand binding properties of human PTX3, in comparison with the classical pentraxins C-reactive protein and serum amyloid P component. Sequencing of Chinese hamster ovary cell-expressed PTX3 revealed that the mature secreted protein starts at residue 18 (Glu). Lectin binding and treatment with N-glycosidase F showed that PTX3 is N-glycosylated, sugars accounting for 5 kDa of the monomer mass (45 kDa). Circular dichroism analysis indicated that the protein consists predominantly of beta-sheets with a minor alpha-helical component. While in gel filtration the protein is eluted with a molecular mass of congruent with900 kDa, gel electrophoresis using nondenaturing, nonreducing conditions revealed that PTX3 forms multimers predominantly of 440 kDa apparent molecular mass, corresponding to decamers, and that disulfide bonds are required for multimer formation. The ligand binding properties of PTX3 were then examined. As predicted based on modeling, inductive coupled plasma/atomic emission spectroscopy showed that PTX3 does not have coordinated Ca2+. Unlike the classical pentraxins CRP and SAP, PTX3 did not bind phosphoethanolamine, phosphocholine, or high pyruvate agarose. PTX3 in solution, bound to immobilized C1q, but not C1s, and, reciprocally, C1q bound to immobilized PTX3. Binding of PTX3 to C1q is specific and saturable with a Kd 7.4 x 10(-8) M as determined by solid phase binding assay. The Chinese hamster ovary cell-expressed pentraxin domain bound C1q when multimerized. Thus, as predicted on the basis of computer modeling, the prototypic long pentraxin PTX3 forms multimers, which differ from those formed by classical pentraxins in terms of protomer composition and requirement for disulfide bonds, and does not recognize CRP/SAP ligands. The capacity to bind C1q, mediated by the pentraxin domain, is consistent with the view that PTX3, produced in tissues by endothelial cells or macrophages in response to interleukin-1 and tumor necrosis factor, may act as a local regulator of innate immunity.