Biomedical subjects

S Meri

Publications and source records attributed to S Meri.

At least 19 recordsLinked to original sources

PubMed2006

Molecular characterization of Echinococcus isolates of cervid origin from Finland and Sweden.

The species Echinococcus granulosus is made up of several genotypic strain groups, whose taxonomical classification is still undetermined. Genotypes in the cervid-wolf life-cycle are poorly known, especially in Europe. In this study, 33 Echinococcus isolates from cervids from Finland and Sweden were characterized using mitochondrial ND1 gene sequencing. In addition, phylogenetic analysis of E. granulosus strains using the mitochondrial ATP6, ND1, ND3 and CO1 genes was performed using maximum likelihood, neighbour-joining and maximum parsimony methods. The Finnish and Swedish cervid isolates were found to represent the genotype G10. In the phylogenetic analyses, the camel (G6), pig (G7), cervid (G8) and Fennoscandian cervid (G10) strains clustered in a well-supported monophyletic group. This group differed clearly from the common sheep (G1) and horse (G4, 'E. equinus') strains, but was closely related to the cattle strain (G5, 'E. ortleppi'). Our results support the previous studies suggesting that the genotypes G6-10 should be separated from the species E. granulosus sensu stricto. However, additional morphological studies are needed, and the relationship to the cattle strain ('E. ortleppi') should be thoroughly evaluated before a final decision of the taxonomical status of the G6-10 group can be made.

Animals↗

PubMed2006

The C-terminus of complement regulator Factor H mediates target recognition: evidence for a compact conformation of the native protein.

The complement inhibitor Factor H has three distinct binding sites for C3b and for heparin, but in solution uses specifically the most C-terminal domain, i.e. short consensus repeats (SCR) 20 for ligand interaction. Two novel monoclonal antibodies (mABs C14 and C18) that bind to the most C-terminal domain SCR 20 completely blocked interaction of Factor H with the ligands C3b, C3d, heparin and binding to endothelial cells. In contrast, several mAbs that bind to the N-terminus and to the middle regions of the molecule showed no or minor inhibitory effects when assayed by enzyme-linked immunosorbent assay (ELISA) and ligand interaction assays. This paradox between a single functional binding site identified for native Factor H versus multiple interaction sites reported for deletion constructs is explained by a compact conformation of the fluid phase protein with one accessible binding site. On zymosan particles mAbs C14 and C18 blocked alternative pathway activation completely. Thus demonstrating that native Factor H makes the first and initial contact with the C terminus, which is followed by N terminally mediated complement regulation. These results are explained by a conformational hypothetical model: the native Factor H protein has a compact structure and only one binding site accessible. Upon the first contact the protein unfolds and exposes the additional binding sites. This model does explain how Factor H mediates recognition functions during complement control and the clustering of disease associated mutations in patients with haemolytic uraemic syndrome that have been reported in the C-terminal recognition domain of Factor H.

Antibodies, Monoclonal↗

PubMed2006

Immunoglobulins and complement factor C4 in adult rhinosinusitis.

We assessed whether complement and its factor C4 or abnormal immunoglobulin levels are associated with chronic or recurrent rhinosinusitis. We used multiple patient and control groups to obtain clinically meaningful data. Adult chronic or recurrent rhinosinusitis and acute purulent rhinosinusitis patients were compared with unselected adults and controls without previous rhinosinusitis. Associated clinical factors were reviewed. Levels of immunoglobulins, plasma C3, C4 and classical pathway haemolytic activity were analysed. C4 immunophenotyping was used to detect C4A and C4B deficiencies as null alleles. Complement was up-regulated in rhinosinusitis. C4A nulls and low IgA, IgG, IgG1, IgG2, IgG3 and IgG4 levels were all more common in chronic or recurrent rhinosinusitis patients than in unselected and healthy controls. We searched for relevant differences between the patient groups. According to stepwise logistic regression analysis, nasal polyposis [odds ratio (OR) 10.64, 95% confidence interval (CI) 2.5-45.7, P = 0.001], bronchial asthma (OR 8.87, 95% CI 2.3-34.9, P = 0.002), C4A null alleles (OR 5.84, 95% CI 1.4-24.9, P = 0.017) and low levels of IgG4 together with either IgG1 or IgG2 (OR 15.25, 95% CI 1.4-166.8, P = 0.026) were more common in chronic or recurrent rhinosinusitis than in acute rhinosinusitis patients. Isolated low IgG subclasses had limited value in patient assessment. C4A null alleles are associated with chronic or recurrent rhinosinusitis, potentially through their effect on immune defence and inflammation control. Multiple clinical and immunological parameters may need to be evaluated when searching for prognostic variables.

Adult↗

PubMed2006

Immunoglobulin uptake and processing by Schistosoma mansoni.

Intravascular Schistosoma mansoni worms seem to take up immunoglobulins from blood by surface Fc-receptors, but the process whereby bound immunoglobulins are processed by the parasite is poorly understood. We here present morphological data suggesting that two distinct main processes are involved: Host immunoglobulins were seen at two distinct locations in the parasite: in the frontal part of the enteric tube, the oesophagus, and as a fine granular staining at the surface and in the subtegumental region. The latter staining pattern corresponds to host immunoglobulin localization in discrete organelle-like aggregates tentatively identified as 'discoid or elongate bodies' at the ultrastructural level using immunogold staining. Immunoglobulin uptake by intravascular worms was also demonstrated in vivo after passive administration of 125I-labelled rabbit and mouse immunoglobulins. Radiolabelled immunoglobulins were taken up by the worms and shown to localize as fine strands running perpendicular to the parasite surface. Our results suggest that intravascular schistosomes take up host immunoglobulins both as part of their enteric digestion and by a surface Fc-receptor-mediated mechanism, involving transport and processing within organelles, 'elongate bodies'. Immunoglobulins taken up by intravascular schistosomes form a distinct organelle-like granules, which seem to be processed within the excretory system of the parasite.

Animals↗

PubMed2006

Minimal residual disease in ovarian cancer as a target for complement-mediated mAb immunotherapy.

Ovarian cancer is potentially well suited for local monoclonal antibody (mAb) immunotherapy, because it remains within the peritoneal cavity for a long period of time before giving rise to distant metastases. At the stage of minimal residual disease, the cells appear to be in a state of dormancy (G(0)) or at least have lower rates of tumour cell proliferation. They should be a promising target for immunotherapy. Here we first examined the cell-cycle expression of CD59 and decay-accelerating factor (DAF; CD55) on four different ovarian carcinoma cell lines, using simultaneous flow cytometric analysis of DNA content or the cell-cycle-specific nuclear proliferation protein Ki67 and CD59 or DAF surface expression. We found that CD59 and DAF are stably expressed throughout the cell cycle. The polyvalent approach to target-independent antigens to improve the efficiency of mAb complement (C)-mediated damages was promising, and tumour cells become sensitive to C damage, when incubated with cross-linked mAb against different tumour-associated antigens. Although, such immune complex-mediated C activation was rather ineffective in killing the cells, it could be potentiated by the addition of blocking mAb against CD59 and DAF. Our results suggest that the activities of intrinsic C regulators must be neutralized to make minimal residual disease a promising target for antibody therapy.

Adenocarcinoma↗

PubMed2006

Relapsing fever spirochetes Borrelia recurrentis and B. duttonii acquire complement regulators C4b-binding protein and factor H.

Relapsing fever is a rapidly progressive and severe septic disease caused by certain Borrelia spirochetes. The disease is divided into two forms, i.e., epidemic relapsing fever, caused by Borrelia recurrentis and transmitted by lice, and the endemic form, caused by several Borrelia species, such as B. duttonii, and transmitted by soft-bodied ticks. The spirochetes enter the bloodstream by the vector bite and live persistently in plasma even after the development of specific antibodies. This leads to fever relapses and high mortality and clearly indicates that the Borrelia organisms utilize effective immune evasion strategies. In this study, we show that the epidemic relapsing fever pathogen B. recurrentis and an endemic relapsing fever pathogen, B. duttonii, are serum resistant, i.e., resistant to complement in vitro. They acquire the host alternative complement pathway regulator factor H on their surfaces in a similar way to that of the less serum-resistant Lyme disease pathogen, B. burgdorferi sensu stricto. More importantly, the relapsing fever spirochetes specifically bind host C4b-binding protein, a major regulator of the antibody-mediated classical complement pathway. Both complement regulators retained their functional activities when bound to the surfaces of the spirochetes. In conclusion, this is the first report of complement evasion by Borrelia recurrentis and B. duttonii and the first report showing capture of C4b-binding protein by spirochetes.

Borrelia↗

PubMed2005

Ascitic complement system in ovarian cancer.

Ovarian cancer spreads intraperitoneally and forms fluid, whereby the diagnosis and therapy often become delayed. As the complement (C) system may provide a cytotoxic effector arm for both immunological surveillance and mAb-therapy, we have characterised the C system in the intraperitoneal ascitic fluid (AF) from ovarian cancer patients. Most of the AF samples showed alternative and classical pathway haemolytic activity. The levels of C3 and C4 were similar to or in the lower normal range when compared to values in normal sera, respectively. However, elevated levels of C3a and soluble C5b-9 suggested C activation in vivo. Malignant cells isolated from the AF samples had surface deposits of C1q and C3 activation products, but not of C5b-9 (the membrane attack complex; MAC). Activation could have become initiated by anti-tumour cell antibodies that were detected in the AFs and/or by changes on tumour cell surfaces. The lack of MAC was probably due to the expression of C membrane regulators CD46, CD55 and CD59 on the tumour cells. Soluble forms of C1 inhibitor, CD59 and CD46, and the alternative pathway inhibitors factor H and FHL-1 were present in the AF at concentrations higher than in serum samples. Despite the presence of soluble C inhibitors it was possible to use AF as a C source in antibody-initiated killing of ovarian carcinoma cells. These results demonstrate that although the ovarian ascitic C system fails as an effective immunological surveillance mechanism, it could be utilised as an effector mechanism in therapy with intraperitoneally administrated mAbs, especially if the intrinsic C regulators are neutralised.

Adenocarcinoma↗

PubMed2004

The hyphal and yeast forms of Candida albicans bind the complement regulator C4b-binding protein.

Candida albicans, an important pathogenic yeast, activates all three pathways of the complement system. To understand how this yeast evades the effects of the activated system, we have analyzed the binding of the classical pathway inhibitor C4b-binding protein (C4BP) by C. albicans. Purified native as well as recombinant C4BP bound dose dependently to the yeast and hyphal forms, as shown by multiple methods, such as confocal microscopy, flow cytometry, a novel enzyme-linked immunosorbent assay, absorption from human serum, and direct binding assays with purified proteins. A prominent binding site was identified at the tip of the germ tube, a structure that is considered important for tissue penetration and pathogenesis. The binding site in C4BP was localized to the two N-terminal complement control protein domains by using recombinant deletion constructs and site-specific monoclonal antibodies. As the alternative pathway inhibitors factor H and FHL-1 also bind to C. albicans, the binding of all three plasma proteins was compared. Simultaneous binding of the classical regulator C4BP and the alternative pathway regulator factor H was demonstrated by confocal microscopy. In addition, FHL-1 competed for binding with C4BP, suggesting that these two related complement regulators bind to the same structures on the yeast surface. The surface-attached C4BP maintains its complement regulatory activities and inactivates C4b. The surface-attached human C4BP serves multiple functions relevant for immune evasion and likely pathogenicity. It inhibits complement activation at the yeast surface and, in addition, mediates adhesion of C. albicans to host endothelial cells.

Binding Sites↗

PubMed2003

Upregulation of major histocompatibility complex class II antigens in hepatocytes in Doberman hepatitis.

Major histocompatibility complex (MHC) class II antigen expression in hepatocytes and its correlation with mononuclear cell infiltration into the liver were studied using immunohistochemical techniques in 38 Dobermans with Doberman hepatitis (DH). Liver biopsy samples were obtained from 18 dogs at the subclinical stage. Autopsy samples were taken from 6 DH dogs euthanized for a reason other than DH, from 14 dogs euthanized because of advanced liver failure and from 6 control Dobermans. Upon examination of the control liver samples, no expression of MHC class II antigens was detected in hepatocytes. By contrast, in 15 of the 18 DH biopsies (83%) and in all 20 DH autopsy liver samples, hepatocytes expressed MHC class II molecules. MHC class II expression was either cytoplasmic or membranous and occurred in conjunction with lymphocyte infiltration. A correlation between the inflammatory reaction and the expression of MHC class II in hepatocytes suggests that the aberrant expression of MHC class II in hepatocytes is induced by cytokines. Hepatocytes presenting a putative MHC class II molecule-associated autoantigen could thus become the target of an immune attack mediated by CD4+ T cells. In addition, corticosteroid treatment was observed to significantly decrease MHC class II expression in DH hepatocytes. Inappropriate MHC class II expression in hepatocytes and mononuclear cell infiltration are suggesting an autoimmune nature for chronic hepatitis in Dobermans.

Animals↗

PubMed2003

Membrane-bound complement regulatory proteins inhibit complement activation by an immunotherapeutic mAb in a syngeneic rat colorectal cancer model.

MAb-mediated immunotherapy offers a potential tool for destroying metastasizing colorectal tumor cells. Promising results have been obtained by using xenograft models. However, overexpression of membrane-bound complement regulatory proteins (mCRP) impedes complement-mediated destruction of tumor cells in vitro. mCRP operate in a species selective manner. Therefore a syngeneic animal model is needed to investigate the contribution of mCRP in mAb-mediated immunotherapy. Here we present a syngeneic rat colorectal carcinoma model, which fulfills the conditions necessary to investigate the effect of mCRP expression on mAb-mediated immunotherapy of metastases of solid tumors.CC531 rat colorectal cancer cells were injected subcapsularly into the liver of syngeneic WAG/Rij rats. Four mAb (MG1(IgG2a), MG2(IgG2a), MG3(IgG3) and MG4(2a)(IgG2a)) directed against CC531 cells, were tested for their complement activating abilities in vitro and tumor homing capacities in vivo. Only MG4(2a) was found to activate complement in vitro and home to the tumor cells in vivo. This mAb induced C3-deposition and C-mediated lysis of CC531 cells in vitro when the effects of the C-inhibitors Crry/p65 and CD59 were neutralized. This implies an important role for these mCRP in restricting the effector functions of tumor-associated mAb on these cells. Although C activation could be induced by MG4(2a) in situ on tumor tissue sections, no deposition of C3 could be found on the tumor cells positive for MG4(2a) in vivo. This suggests that complement activation in vivo was inhibited by mCRP. The results indicate the suitability of this syngeneic animal model for studying the effects of mAb immunotherapy. However, the effect of mCRP on tumor cells need to be overcome, e.g. by the use of mAb against tumor antigens and mCRP.

Animals↗

PubMed2003

Molecular genetic characterization of the Fennoscandian cervid strain, a new genotypic group (G10) of Echinococcus granulosus.

The northern biotype of Echinococcus granulosus occurs in North America and northern Eurasia in life-cycles involving cervids. Previously, cervid isolates of E. granulosus from North America have been characterized using molecular genetic techniques as the G8 genotype. In this study, 5 isolates of E. granulosus were collected from 4 reindeer and 1 moose in north-eastern Finland. DNA sequences within regions of mitochondrial cytochrome c oxidase I (COI) and NADH dehydrogenase I (NI)I) genes and the internal transcribed spacer 1 (ITS-1) fragment of the ribosomal DNA were analysed. The mitochondrial nucleotide sequences were identical in all isolates, but high sequence variation was found in the ITS-1 region. Mitochondrial and nuclear sequences of the Finnish cervid E. granulosus and the camel strain (G6) of E. granulosus resembled closely each other. According to phylogenetic analyses, the Finnish isolates have close relationships also with the pig (G7) and cattle (G5) strains. Although some similarities were found with the previously published North American cervid strain (G8), particularly in the NDI sequence and some of the ITS-1 clones, the Finnish E. granulosus form represents a distinct, previously undescribed genotype of E. granulosus. The novel genotype is hereby named as the Fennoscandian cervid strain (G10).

Animals↗

PubMed2003

Release of endogenous anti-inflammatory complement regulators FHL-1 and factor H protects synovial fibroblasts during rheumatoid arthritis.

Rheumatoid arthritis is a chronic inflammatory disease of unknown aetiology predominantly affecting cells and tissues of synovial joints. Here we show that the two important complement regulators FHL-1 and factor H play a protective anti-inflammatory role in rheumatoid arthritis. Expression analyses at the mRNA- and protein level show in vitro expression and secretion of both regulators by synovial fibroblasts derived from patients with rheumatoid arthritis. Similarly the two regulators are synthesized in vivo in diseased synovial tissue, and in particular synovial lining cells express high levels of FHL-1. The anti-inflammatory role of these regulators in rheumatoid arthritis is highlighted by their induction with IFN-gamma and dexamethasone, whilst the pro-inflammatory cytokine TNF-alpha had no effect. Transient transfection experiments with various FHL-1/factor H promoter-luciferase reporter constructs into cells of distinct origin show independent cell and tissue specific promoter regulated transcription of these two regulators. The inducible expression, specifically of FHL-1 has physiological consequences. By binding directly to surfaces the released proteins protect cells from inflammatory damage and complement-mediated cell lysis. This study shows a novel protective and anti-inflammatory role of the two important complement regulators FHL-1 and factor H in rheumatoid arthritis and suggests a disease controlling role of the two proteins.

Arthritis, Rheumatoid↗

PubMed2002

Secretion of soluble complement inhibitors factor H and factor H-like protein (FHL-1) by ovarian tumour cells.

We observed that the soluble complement regulators factor H and factor H-like protein were abundantly present in ascites samples as well as in primary tumours of patients with ovarian cancer. RT-PCR and immunoblotting analyses showed that the two complement inhibitors were constitutively produced by the ovarian tumour cell lines SK-OV-3 and Caov-3, but not PA-1 or SW626 cells. The amounts of factor H-like protein secreted were equal to those of factor H. This is exceptional, because e.g. in normal human serum the concentration of factor H-like protein is below 1/10th of that of factor H. In ascites samples the mean level of factor H-like protein (130+/-55 microg ml(-1)) was 5.5-fold higher than in normal human serum (24+/-3 microg ml(-1)). Ovarian tumour cells thus preferentially synthesise factor H-like protein, the alternatively spliced short variant of factor H. The tumour cells were found to bind both (125)I-labelled factor H and recombinant factor H-like protein to their surfaces. Surprisingly, the culture supernatants of all of the ovarian tumour cell lines studied, including those of PA-1 and SW626 that did not produce factor H/factor H-like protein, promoted factor I-mediated cleavage of C3b to inactive iC3b. Subsequently, the PA-1 and SW626 cell lines were found to secrete a soluble form of the membrane cofactor protein (CD46). Thus, our studies reveal two novel complement resistance mechanisms of ovarian tumour cells: (i) production of factor H-like protein and factor H and (ii) secretion of soluble membrane cofactor protein. Secretion of soluble complement inhibitors could protect ovarian tumour cells against humoral immune attack and pose an obstacle for therapy with monoclonal antibodies.

Ascitic Fluid↗

PubMed2002

Factor H family proteins: on complement, microbes and human diseases.

At present, the human Factor H protein family represents seven multidomain, multifunctional serum proteins. This group includes the complement and immune regulators Factor H, the Factor H-like protein 1 (FHL-1) and five Factor H-related proteins proteins (FHR-1, -2, -3, -4 and -5). Each is exclusively composed of individually folded protein domains, termed short consensus repeats (SCRs) or complement control modules. Structure-function analyses allowed the localization of the complement regulatory domain of Factor H and FHL-1 in the N-terminal region within SCRs 1-4. In addition, multiple binding sites for C3b, heparin and microbial surface proteins were localized in the N-terminus, within the middle region and also in the C-terminus of Factor H and FHL-1. Recent results show a central role for the C-terminus of Factor H, i.e. SCRs 19-20. These particular domains are conserved in all FHRs identified so far, include contact points for C3b, heparin and microbial surface proteins and represent a 'hot-spot' for gene mutations in patients that suffer from the Factor H-associated form of haemolytic uraemic syndrome.

Borrelia↗

PubMed2002

Differential expression of cytokines (IL-2, IFN-gamma, IL-10) and adhesion molecules (VCAM-1, LFA-1, CD44) between spleen and lymph nodes associates with remission in chronic relapsing experimental autoimmune encephalomyelitis.

We have recently established chronic relapsing experimental autoimmune encephalomyelitis (CR-EAE) in SJL mice with a modified protocol. In this model, splenectomy aborts the relapsing-remitting course of the disease, and adoptive transfer of lymphocytes of the local draining lymph nodes (LNs) to naive recipients exacerbates the disease. Adoptive transfer of splenic cells converted acute EAE into CR-EAE in the naive recipients. In light of the different roles of the spleen and LNs in the evolution of CR-EAE, we examined by semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) whether a differential mRNA expression profile of cytokines and cellular adhesion molecules (CAMs) in spleen versus LN was associated with relapse or remission in CR-EAE. All the cytokines tested (interleukin-1beta (IL-1beta), IL-2, IL-4, IL-7, IL-10, interferon-gamma (IFN-gamma)) as well as CAMs (ICAM-1, ICAM-2, VCAM-1, LFA-1 and CD44) were expressed at substantial levels in both spleen and LNs. Interestingly, disease remission was found to be associated with an increased mRNA expression of IL-2 and IFN-gamma in LNs and a decreased IL-10 mRNA level in the spleen. On the other hand, an increased mRNA expression of VCAM-1, LFA-1 and CD44 was observed in the spleens in comparison with that in LNs of mice, with remission. During relapses, mRNA expression of the tested molecules did not significantly differ between spleens and LNs. Our results suggest that a differential and polarized expression profile of certain cytokines and CAMs in spleen versus LN could provide molecular correlates of the cyclic pathogenesis of CR-EAE.

Animals↗

PubMed2002

The yeast Candida albicans binds complement regulators factor H and FHL-1.

The human facultative pathogenic yeast Candida albicans causes mucocutaneous infections and is the major cause of opportunistic fungal infections in immunocompromised patients. C. albicans activates both the alternative and classical pathway of the complement system. The aim of this study was to assay whether C. albicans binds human complement regulators in order to control complement activation at its surface. We observed binding of two central complement regulators, factor H and FHL-1, from normal human serum to C. albicans by adsorption assays, immunostaining, and fluorescence-activated cell sorter (FACS) analyses. Specificity of acquisition was further confirmed in direct binding assays with purified proteins. The surface-attached regulators maintained their complement regulatory activities and mediated factor I-dependent cleavage of C3b. Adsorption assays with recombinant deletion mutant proteins were used to identify binding domains. Two binding sites were localized. One binding domain common to both factor H and FHL-1 is located in the N-terminal short consensus repeat domains (SCRs) 6 and 7, and the other one located in C-terminal SCRs 19 and 20 is unique to factor H. These data indicate that by surface acquisition of host complement regulators, the human pathogenic yeast C. albicans is able to regulate alternative complement activation at its surface and to inactivate toxic complement activation products.

Binding Sites↗

PubMed2001

Complement C4 deficiency and HLA homozygosity in patients with frequent intraoral herpes simplex virus type 1 infections.

Three consecutive patients with no apparent immunodeficiency who had frequent intraoral herpes simplex type 1 recurrences, a rare complication of herpes simplex virus infection, were found to have a total deficiency of either the A or B isotype of the complement component C4 and to be homozygous for the studied HLA antigens. A combination of HLA homozygosity, which may lead to impaired T cell recognition of viral peptides, and deficiency in the classical complement pathway, which can compromise virus neutralization, may predispose to severe and frequent herpes simplex virus infections.

Adult↗

PubMed2001

Regulation of complement classical pathway by association of C4b-binding protein to the surfaces of SK-OV-3 and Caov-3 ovarian adenocarcinoma cells.

The role of fluid-phase regulators of complement is to inhibit excessive complement activation and maintain homeostasis in blood. By binding to and inactivating complement components on cell surfaces, they can also protect autologous cells from complement-mediated cytotoxicity and phagocytosis. In this study, we wanted to find out whether C4b-binding protein (C4bp), a fluid-phase regulator of the classical complement pathway, could directly bind to cell surfaces in a functionally active form. After screening several malignant cell lines, we observed that the ovarian adenocarcinoma cell lines SK-OV-3, Caov-3, and SW626 were capable of binding C4bp. Binding tests with recombinant deletion mutants suggested that the primary binding site on C4bp is located on the alpha-chain complement control protein 4 domain. Functional tests showed that tumor cell-bound C4bp retained its cofactor activity for factor I-mediated inactivation of C4b, thus increasing the control of classical complement pathway activation on the surfaces of these cells. These results demonstrate a novel mechanism of complement regulation on cell surfaces, particularly on those of malignant ovarian tumor cells.

Adenocarcinoma↗