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S Meri

Publications and source records attributed to S Meri.

At least 37 records · Page 2Linked to original sources
PubMed1993

Regulation of CD59 expression on the human endothelial cell line EA.hy 926.

CD59 (protectin) is an 18-20-kDa inhibitor of the membrane attack complex of complement. It protects homologous cells from complement-mediated damage and has been shown to be present on the endothelial cell membranes both in vitro and in vivo. In this study we observed that the surface expression of CD59 on the cultured EA.hy 926 endothelial cell line can be up-regulated to an approximately threefold higher level after a 72-h stimulation by the protein kinase C inducers phorbol-12-myristate-13 acetate (PMA; 10 nM) and calcium ionophore, A23187 (100 nM). Similarly, an increase in the level of CD59 expression was seen by the protein kinase A inducer dibutyryl-cyclic adenosine monophosphate. In Northern blot analysis increases were observed in CD59 mRNA expression, particularly in the level of the longest 1.9-kb, 2.1-kb and 5.8-kb transcripts. A functional significance for the increased CD59 expression was implied by an observed increased resistance of the PMA-stimulated EA.hy 926 cells to complement-mediated cell lysis.

Antigens, CD↗
PubMed1993

Regulation of natural killer cell activity by transforming growth factor-beta and prostaglandin E2.

The separate and combined effects of transforming growth factor-beta 1 (TGF-beta 1) and prostaglandin E2 on human natural killer (NK) activity were studied. Peripheral blood lymphocytes (PBL) and large granular lymphocytes (LGL, 70-90% purity) were used as effector cells and K562 as targets. Overnight incubation of the effector cells with TGF-beta 1 resulted in a significant inhibition of NK activity. TGF-beta 1 did not influence the expression of CD3, CD16, CD18 or CD56 antigens on PBL. Combination of TGF-beta 1 with indomethacin gave the same NK-suppressive effect as TGF-beta 1 alone, showing that the inhibition of NK activity by TGF-beta 1 is not due to an increase in PGE2 levels. TGF-beta did not influence cAMP level in PBL whereas PGE2 significantly increased it. On the other hand, TGF-beta 1 and PGE2 showed an additive inhibitory effect on NK activity. TGF-beta 1 did not reduce the binding of PBL and LGL to K562. PGE2 suppressed the binding and TGF-beta 1 did not influence this suppression. TGF-beta 1 also suppressed IL-2-induced activation of NK activity and increase of expression of the granule proteins granzyme A and perforin. PGE2 did not appear to affect granzyme A and perforin contents. The results indicate that TGF-beta 1 and PGE2 suppress NK activity by different mechanisms.

Cells, Cultured↗
PubMed1993

Immunolocalization and characterization of the rat analogue of human CD59 in kidney and glomerular cells.

CD59, a potent inhibitor of the human membrane attack complex (MAC) of complement, is present on many different tissues throughout the body. Recently we identified and characterized the rat analogue of CD59 and produced a number of monoclonal antibodies (mAb). We have now used these antibodies to demonstrate, by immunofluorescence microscopy, that rat CD59 was widely expressed in the rat kidney. Staining of renal sections revealed the presence of rat CD59 in abundance in the glomerulus, collecting ducts and distal tubules. Staining was abolished by treatment of sections with phosphatidylinositol-specific phospholipase C (PIPLC). Rat mesangial cells also stained strongly for rat CD59, giving an intensely granular staining pattern. In complement attack experiments the cultured mesangial cells were rendered more susceptible to lysis by rat or human complement after preincubation with the anti-inhibitor mAb. The results demonstrate that the rat analogue of CD59 is present and functionally active in rat renal tissue. The protective effect of CD59 against MAC-mediated tissue injury can now be examined in rat models of human renal disease.

Animals↗
PubMed1993

Regulation of complement membrane attack complex formation in myocardial infarction.

Recent studies have suggested that the complement (C) system is involved in the development of tissue injury of myocardial infarction. As it is not known why the strictly controlled C system starts to react against autologous heart tissue, we have analyzed the expression of various membrane regulators of C (CR1, DAF, MCP, CD59, C8 binding protein) and the pattern of deposition of C components and plasma C regulators (C4b binding protein and vitronectin) in normal (n = 7) and infarcted (n = 13) human myocardium. In the infarcted myocardium deposits of the C membrane attack complex (MAC) were observed by immunofluorescence microscopy, and lesions resembling the transmembrane channels of MAC were detected by transmission electron microscopy. CD59 and C8 binding protein were strongly expressed by muscle cells of normal myocardial tissue. Little or no CR1, MCP, and DAF was observed on these cells. The assembly of MAC was accompanied by the deposition of vitronectin (S-protein) and C4b binding protein in the infarcted areas of myocardium. In accordance with our earlier results the expression of CD59 but not of C8 binding protein was clearly diminished in the lesions. The results show that C8 binding protein, vitronectin, and C4b binding protein do not prevent complement attack against the infarcted myocardium but rather become codeposited with the MAC. Ischemia-induced transformation of nonviable cells into complement activators, acquired loss of resistance to the MAC by shedding of CD59, and recruitment of multifunctional serum proteins by MAC could thus constitute a general process aimed at the clearance of injured tissue.

Aged↗
PubMed1993

Co-deposition of clusterin with the complement membrane attack complex in myocardial infarction.

Clusterin is a multi-functional plasma glycoprotein that has been shown to inhibit formation of the complement membrane attack complex (MAC) by preventing the association of terminal complement complexes with target cell membranes. Recent studies have suggested that complement activation is involved in the development of tissue injury of myocardial infarction. In this study we observed that clusterin is selectively deposited in the infarcted areas of human myocardium. Clusterin deposits were observed in the heart tissue of 10 patients whose infarcted lesions were 8 hr to 14 days old, but not in patients who died from other causes. Clusterin co-localized with the MAC on the surface of damaged cardiomyocytes. In normal myocardium only endothelial lining of blood vessels occasionally stained positive for clusterin. The 80,000 MW clusterin was also detected by Western blot analysis in extracts of myocardial infarction lesions, but only faintly in extracts of normal heart. As clusterin has apparently failed in protecting myocardium against complement-mediated cell injury its main role might be to participate in the clearance of damaged and necrotic tissue together with the MAC.

Blotting, Western↗
PubMed1992

Activation of the alternative pathway of complement by monoclonal lambda light chains in membranoproliferative glomerulonephritis.

Immunopathological evidence suggests that activation of the alternative pathway of complement (AP) is involved in membranoproliferative glomerulonephritis (MPGN) and in immunoglobulin A nephropathy. In this report we describe an AP dysfunction-associated factor that was isolated from the serum and urine of a patient with hypocomplementemic MPGN. Extensive glomerular deposits of C3, properdin, and of the terminal complement components were observed in the kidney of the patient. In her serum the AP hemolytic activity was virtually absent. When mixed with fresh normal serum, the patient's serum induced a 96% C3 conversion during a 30-min incubation at +37 degrees C. This activity was found to be due to a circulating factor that by immunochemical characterization proved to be a 46-kD monoclonal immunoglobulin lambda light (L) chain dimer (lambda L). Purified lambda L, but not control lambda or kappa L chains from patients with L chain disease, activated the AP in a dose- and ionic strength-dependent manner. Functionally, lambda L was differentiated from C3 nephritic factor (an autoantibody against the AP C3 convertase, C3bBb) by its inability to bind to and stabilize the C3bBb enzyme. Instead, lambda L was observed to interact directly with the AP control factor H. Thus, lambda L represents a novel type of immunoglobulin-related AP-activating factor with the capacity to initiate alternative complement pathway activation in the fluid phase.

Antibodies, Monoclonal↗
PubMed1992

Loss of expression of protectin (CD59) is associated with complement membrane attack complex deposition in myocardial infarction.

BACKGROUND: Protectin (CD59) is a recently discovered inhibitor of the complement membrane attack complex (MAC). In the present study we investigated expression of protectin in human heart and examined the relationship between MAC deposition and protectin in myocardial infarction. EXPERIMENTAL DESIGN: Myocardial tissue specimens were obtained at autopsy from patients who had died of myocardial infarction (n = 10) or other causes (n = 5). MAC and protectin were detected by indirect immunofluorescence microscopy analysis in the heart sections by using antibodies against individual components of MAC, MAC neoantigens and protectin. Myocardial protectin was purified by affinity chromatography and compared with the previously characterized erythrocyte and urinary protectins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, N-terminal amino acid sequencing, and testing its ability to bind to the terminal complement complex. The possible glycophosphoinositol-type anchorage of protectin in the heart was examined by treating myocardial sections with glycophosphoinositol-specific phospholipase C. RESULTS: Immunoblotting and immunofluorescence analysis showed expression of protectin in the sarcolemmal membranes of normal myocardium. Protectin purified from normal human heart tissue had the same molecular weight and N-terminal amino acid sequence as CD59 purified from urine. In sucrose density ultracentrifugation analysis it was observed to bind efficiently to the SC5b-8 complex. In normal myocardium the expression of CD59 was sensitive to treatment with glycophosphoinositol-specific phospholipase C. The expression of CD59 was lost or clearly diminished in infarcted lesions aged 1-14 days. Loss of CD59 expression was accompanied by concomitant deposition of the MAC within the CD59-negative lesions. In border areas between an infarcted lesion and normal tissue, CD59 often appeared in small vesicles, suggesting shedding as a possible mechanism for its removal. CONCLUSIONS: Glycophosphoinositol-anchored CD59 is expressed in the sarcolemmal membranes of normal heart but lost from infarcted myocardium. Acquired loss of resistance to autologous complement and subsequent complement attack may thus be involved in the pathophysiology of myocardial infarction.

Aged↗
PubMed1992

Level of plasma prekallikrein and its inhibitors in reactors and nonreactors during intravenous enhancement with contrast media.

Complex contact activation systems may play a major role in the side effects of i.v. contrast media (CM). This is why quantitative measurements of several factors (plasma prekallikrein, hematocrit (hct), alpha-2-macroglobulin, alpha-1-antitrypsin, and C1-esterase inhibitor) were determined prior to and following the injection of CM during body CT examination in 5 patient groups, each (n = 10) receiving one of 5 different CM, including ioxaglate, meglumine iodamide, metrizamide, iohexol, and meglumine diatrizoate. The initial plasma prekallikrein level was available from 45 patients and was statistically lower in reactors (mean 90.6 mumol TAMe/ml/h; n = 13) than in nonreactors (mean 107 mumol TAMe/ml/h; n = 32) (p = 0.006), but there was no statistically significant difference in the decrease of plasma prekallikrein before and at 5 min after the injection for those 2 groups. The initial plasma C1-esterase inhibitor level was lower in reactors, while the plasma alpha-2-macroglobulin level was higher in that group than in nonreactors. The results indicate that the measurement of plasma prekallikrein combined with plasma C1-esterase inhibitor and alpha-2-macroglobulin measurement could be useful when predicting which patients are prone to CM reactions.

Blood Proteins↗
PubMed1991

Localization of the heparin-binding site on complement factor H.

Factor H is a regulator of complement activation and, in this capacity, it prevents activation of the alternative pathway on host cells and tissues when it recognizes markers on these surfaces. This report describes the binding characteristics and location of the site on factor H that is responsible for host recognition. Factor H was found to bind a variety of polyanions, including heparin, heparan sulfate, dextran sulfate, and clusters of sialic acid. In heparin-agarose binding assays it exhibited an affinity for heparin only 2-fold weaker than that of antithrombin III. Factor H exhibited little or no affinity for polyaspartic acid or bacterial colominic acid (polysialic acid). Factor H (Mr 150,000 with approximate dimensions of 30 x 600 A) is composed of 20 highly homologous domains (SCRs) that are arranged as beads on a string. Polyanions were found to block a tryptic cleavage site in domain 15, and a photoaffinity-tagged heparin probe labeled the region between domains 12 and 15. Affinity chromatography of tryptic fragments on heparin-Sepharose confirmed that this region contained the heparin-binding site. CNBr cleavage at Met787 located between SCRs 13 and 14 split the photoaffinity-tagged region. Sequence analysis strongly suggests that domain 13 contains the primary site of polyanion binding. Factor H expresses its complement regulatory function through a site located in domains 4-6 where C3b binds. Thus, the polyanion-binding site that regulates the affinity of factor H for C3b appears to reside more than 200 A away from the C3b-binding site.

Amino Acid Sequence↗
PubMed1991

The complement-inhibiting protein, protectin (CD59 antigen), is present and functionally active on glomerular epithelial cells.

Protectin (CD59 antigen) is a 20-kD phosphatidyl-inositol-linked membrane protein that inhibits formation of the membrane attack complex (MAC) of complement on homologous cells. Although the antigen has been identified in a number of human tissues, until recently a functional role had been demonstrated only in circulating cells. Using immunofluorescence techniques we have shown the presence of protectin on human glomerular epithelial cells (GEC) in culture and on GEC, tubular epithelial cells and endothelial cells in frozen sections of normal human renal cortex. In addition, we present evidence that this protein functions in protection of GEC from homologous complement: cultured cells incubated with the Fab2 fragment of a monoclonal anti-protein antibody were markedly more susceptible to killing by homologous serum than were cells in the absence of Fab2 anti-protectin. These findings suggest that this protein may be important in the maintenance of glomerular integrity in vivo, and may be of relevance in certain renal diseases.

Animals↗
PubMed1991

Acute-phase proteins during hemodialysis: correlations with serum interleukin-1 beta levels and different dialysis membranes.

The effects of hemodialysis (HD) on the levels of serum amyloid A (SAA), C-reactive protein (CRP) and interleukin-1 beta (IL-1 beta) were studied in 8 patients. Bicarbonate dialysate was used exclusively, and three different membranes, Cuprophan (CU), cellulose acetate (CA), and polymethylmetachrylate (PMMA) were compared. The SAA levels increased significantly with each membrane. With CU, they rose from 4.0 +/- 2.0 (mg/l, mean +/- SEM) to 9.6 +/- 2.8 at 60 min and to 15.0 +/- 4.9 at 240 min. The values with CA were 3.8 +/- 2.1, 15.3 +/- 5.6, and 23.8 +/- 3.9; and with PMMA 2.4 +/- 1.3, 12.1 +/- 5.6, and 12.1 +/- 5.9, respectively. The alterations of SAA neither correlated with the weight loss nor the increase of serum albumin during dialysis. The CRP values showed insignificant changes. The IL-1 beta levels rose with CU from 87 +/-18 (ng/l) to 155 +/- 33 at 60 min and to 172 +/- 47 at 240 min. With CA, the values were 67 +/- 14, 198 +/- 46, and 121 +/- 23, and with PMMA 63 +/- 13, 246 +/- 93, and 211 +/- 86, respectively. These results did not correlate with the effects of the membranes on complement activation. It is concluded that the release of cytokines during HD apparently leads to a rapid synthesis of acute-phase proteins as a sign of inflammation. Thus, SAA may be used as one indicator of the biocompatibility of HD treatment.

Adult↗
PubMed1991

Distribution of protectin (CD59), a complement membrane attack inhibitor, in normal human tissues.

Protectin (CD59) is a recently discovered 18-20 kDa glycoprotein that effectively inhibits lysis by the membrane attack complex of the homologous complement system. This glycoprotein is widely distributed on the membranes of human blood cells (erythrocytes and leukocytes). By using immunofluorescence microscopy, protectin was observed in vascular endothelia throughout the body and in extravascular tissues. Cells expressing protectin were also found in ductal epithelia of pancreatic, biliary, and salivary systems, bronchi, and kidney collecting ducts. Furthermore, protectin was expressed in the epidermis and in the syncytiotrophoblast of placenta. The expression of protectin in endothelia, in various epithelial cells, and in placenta presumably protects autologous tissues and the fetoplacental unit from complement-mediated damage.

Antigens, CD↗
PubMed1990

Human protectin (CD59), an 18-20-kD homologous complement restriction factor, does not restrict perforin-mediated lysis.

Human protectin (CD59) is an 18-20-kD membrane glycoprotein that restricts lysis of human erythrocytes and leukocytes by homologous complement. By directly incorporating protectin into membranes of heterologous cells we observed that protectin did not prevent perforin-mediated killing, whereas complement killing was effectively restricted. Further, no significant enhancement of cell-mediated killing or target killing by purified perforin was observed with anti-protectin antibodies. Thus, in contrast with complement lysis, restriction of lysis by protectin does not apply to cell-mediated killing.

Animals↗
PubMed1990

A mechanism of activation of the alternative complement pathway by the classical pathway: protection of C3b from inactivation by covalent attachment to C4b.

In this work we studied the role of the classical pathway complement component C4b in the activation of the alternative pathway. It was found that nascent C3b attaches with high efficiency to C4b and that C3b in C4bC3b complexes is protected from inactivation by factors H and I. Activation of C3 by factors B and D in the presence of Mg2+ ions and excess C4b led to 35% incorporation of nascent C3b into C4bC3b complexes in the fluid phase. In comparison, when human IgG was tested as an acceptor under similar conditions, only 12% of generated C3b was incorporated into IgGC3b complexes. The half-life time of dissociation of C3b from purified C4bC3b complexes was approximately 2.3 h at 37 degrees C. C4b in these complexes protected C3b from inactivation as effectively as any known alternative pathway activator. Thus, C3b bound to C4b was tenfold more stable than free C3b or C3b bound to a nonactivating surface. In comparison, the protection provided by attachment to human IgG was only 67% of that of C4b. The results provide an explanation for observations of alternative pathway recruitment following classical pathway activation and for the stability of the classical pathway C5 convertase on surfaces which do not provide protection for C3b from factors H and I.

Complement C3-C5 Convertases↗
PubMed1990

Discrimination between activators and nonactivators of the alternative pathway of complement: regulation via a sialic acid/polyanion binding site on factor H.

The alternative complement pathway is capable of discriminating human cells and tissues from a wide variety of potential pathogens. It has been recently demonstrated that attachment of complement component C3b to activator-derived molecules (e.g., small polysaccharides) restricts inactivation of C3b by factors H and I in a manner similar to activator surfaces. It is now shown that restriction is reversed by certain soluble polyanions (e.g., sialoglycopeptides, heparin, or dextran sulfate) that mimic the effects of sialic acid and glycosaminoglycans on human cells and tissues. Fluid-phase polyanions enhanced binding of factor H to C3b attached to activating particles, indicating that the effect resulted from increased affinity between C3b and factor H. The enhancement was specific for activator-bound C3b since no enhancement was observed on nonactivating particles. While several polyanions could cause this effect, some polyanions could not, indicating specificity. The active polyanions also inhibited lysis of cells via the alternative pathway. The binding site for sialic acid appears to reside on factor H, since factor H bound to heparin-agarose and to sialic acid-bearing fetuinagarose, whereas C3b bound to neither under the same conditions. These observations suggest that occupation of a specific site on factor H by polyanions induces an increase in the C3b-H affinity, resulting in discrimination of host cells and tissues from alternative pathway-activating foreign cells.

Animals↗
PubMed1990

Acute schistosomiasis mansoni in Finnish hunters visiting Africa: need for appropriate diagnostic serology.

Three symptomatic and 3 asymptomatic patients with acute schistosomiasis mansoni are described. The index case presented with fever and eosinophilia 4-6 weeks after swimming in the Pipi River of the Central African Republic, suggesting acute schistosomiasis (Katayama fever). A fortunate early diagnosis led to early treatment of these schistosomiasis patients. Diagnosis was obtained based on the finding of one Schistosoma mansoni egg in the index case and positive serology in all cases. A commercially available passive haemagglutination test for serum bilharzia antibodies was negative in all cases prior to, and 2 weeks after treatment. However, antibodies against gut-associated antigens (GAA) of adult S. mansoni worms could be demonstrated using the indirect immunofluorescence technique. These cases illustrate the importance of using appropriate diagnostic assays for the early demonstration of infection by schistosomes in previously unexposed "nonimmune" patients with atypical symptoms and in asymptomatic individuals at risk even after brief exposure to schistosome-containing water in endemic countries. Careful (and repeated) stool examination and appropriate serological tests are the keys to prompt diagnosis of S. mansoni infection.

Adult↗
PubMed1990

Human protectin (CD59), an 18,000-20,000 MW complement lysis restricting factor, inhibits C5b-8 catalysed insertion of C9 into lipid bilayers.

Human cells are relatively resistant to lysis by the homologous complement system. Here we describe the mechanism of action of a recently discovered and widely distributed 18,000-20,000 molecular weight (MW) membrane glycoprotein (CD59), which appears to act as a major protective element against complement-mediated lysis (hence called protectin). When incorporated into heterologous erythrocyte membranes, protectin efficiently prevented cell lysis by human serum. Neutralization with antibody of the naturally occurring protectin on human erythrocytes or on nucleated K562 cells increased their susceptibility to lysis by homologous complement. During complement activation, protectin became incorporated into the membrane attack complex (MAC). By interacting with newly exposed regions in the C5b-8 complex and in aggregating C9 it limited the number of C9 molecules associating with the C5b-8 complex to a C8:C9 ratio of 1:1.5 instead of a normal average of 1:3.5. The results demonstrate directly that protectin is a powerful inhibitor of complement cytolysis and acts by inhibiting the C5b-8 catalysed insertion of C9 into the lipid bilayer.

Antigens, Differentiation↗