| 1. |
- Potempa, Michal, et al.
(författare)
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Binding of complement inhibitor C4b-binding protein contributes to serum resistance of Porphyromonas gingivalis.
- 2008
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Ingår i: Journal of immunology. - 1550-6606. ; 181:8, s. 5537-5544
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Tidskriftsartikel (refereegranskat)abstract
- The periodontal pathogen Porphyromonas gingivalis is highly resistant to the bactericidal activity of human complement, which is present in the gingival crevicular fluid at 70% of serum concentration. All thirteen clinical and laboratory P. gingivalis strains tested were able to capture the human complement inhibitor C4b-binding protein (C4BP), which may contribute to their serum resistance. Accordingly, in serum deficient of C4BP, it was found that significantly more terminal complement component C9 was deposited on P. gingivalis. Moreover, using purified proteins and various isogenic mutants, we found that the cysteine protease high molecular weight arginine-gingipain A (HRgpA) is a crucial C4BP ligand on the bacterial surface. Binding of C4BP to P. gingivalis appears to be localized to two binding sites: on the complement control protein 1 domain and complement control protein 6 and 7 domains of the alpha-chains. Furthermore, the bacterial binding of C4BP was found to increase with time of culture and a particularly strong binding was observed for large aggregates of bacteria that formed during culture on solid blood agar medium. Taken together, gingipains appear to be a very significant virulence factor not only destroying complement due to proteolytic degradation as we have shown previously, but was also inhibiting complement activation due to their ability to bind the complement inhibitor C4BP.
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| 2. |
- Vogt, Leonie M., et al.
(författare)
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Apolipoprotein E Triggers Complement Activation in Joint Synovial Fluid of Rheumatoid Arthritis Patients by Binding C1q
- 2020
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Ingår i: Journal of Immunology. - : American Association of Immunologists. - 0022-1767 .- 1550-6606. ; 204:10, s. 2779-2790
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Tidskriftsartikel (refereegranskat)abstract
- We identified apolipoprotein E (ApoE) as one of the proteins that are found in complex with complement component C4d in pooled synovial fluid of rheumatoid arthritis (RA) patients. Immobilized human ApoE activated both the classical and the alternative complement pathways. In contrast, ApoE in solution demonstrated an isoform-dependent inhibition of hemolysis and complement deposition at the level of sC5b-9. Using electron microscopy imaging, we confirmed that ApoE interacts differently with C1q depending on its context; surface-bound ApoE predominantly bound C1q globular heads, whereas ApoE in a solution favored the hinge/stalk region of C1q. As a model for the lipidated state of ApoE in lipoprotein particles, we incorporated ApoE into phosphatidylcholine/phosphatidylethanolamine liposomes and found that the presence of ApoE on liposomes increased deposition of C1q and C4b from serum when analyzed using flow cytometry. In addition, posttranslational modifications associated with RA, such as citrullination and oxidation, reduced C4b deposition, whereas carbamylation enhanced C4b deposition on immobilized ApoE. Posttranslational modification of ApoE did not alter Clq interaction but affected binding of complement inhibitors factor H and C4b -binding protein. This suggests that changed ability of C4b to deposit on modified ApoE may play an important role. Our data show that posttranslational modifications of ApoE alter its interactions with complement. Moreover, ApoE may play different roles in the body depending on its solubility, and in diseased states such as RA, deposited ApoE may induce local complement activation rather than exert its typical role of inhibition.
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| 3. |
- Lipcsey, Miklós, et al.
(författare)
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The Outcome of Critically Ill COVID-19 Patients Is Linked to Thromboinflammation Dominated by the Kallikrein/Kinin System
- 2021
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Ingår i: Frontiers in Immunology. - : Frontiers Media S.A.. - 1664-3224. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- An important manifestation of severe COVID-19 is the ARDS-like lung injury that is associated with vascular endothelialitis, thrombosis, and angiogenesis. The intravascular innate immune system (IIIS), including the complement, contact, coagulation, and fibrinolysis systems, which is crucial for recognizing and eliminating microorganisms and debris in the body, is likely to be involved in the pathogenesis of COVID-19 ARDS. Biomarkers for IIIS activation were studied in the first 66 patients with COVID-19 admitted to the ICU in Uppsala University Hospital, both cross-sectionally on day 1 and in 19 patients longitudinally for up to a month, in a prospective study. IIIS analyses were compared with biochemical parameters and clinical outcome and survival. Blood cascade systems activation leading to an overreactive conjunct thromboinflammation was demonstrated, reflected in consumption of individual cascade system components, e.g., FXII, prekallikrein, and high molecular weight kininogen and in increased levels of activation products, e.g., C4d, C3a, C3d,g, sC5b-9, TAT, and D-dimer. Strong associations were found between the blood cascade systems and organ damage, illness severity scores, and survival. We show that critically ill COVID-19 patients display a conjunct activation of the IIIS that is linked to organ damage of the lung, heart, kidneys, and death. We present evidence that the complement and in particular the kallikrein/kinin system is strongly activated and that both systems are prognostic markers of the outcome of the patients suggesting their role in driving the inflammation. Already licensed kallikrein/kinin inhibitors are potential drugs for treatment of critically ill patients with COVID-19.
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| 4. |
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| 5. |
- Martin, Myriam, et al.
(författare)
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Citrullination of C1-inhibitor as a mechanism of impaired complement regulation in rheumatoid arthritis
- 2023
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Ingår i: Frontiers in Immunology. - : Frontiers Media S.A.. - 1664-3224. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundDysregulated complement activation, increased protein citrullination, and production of autoantibodies against citrullinated proteins are hallmarks of rheumatoid arthritis (RA). Citrullination is induced by immune cell-derived peptidyl-Arg deiminases (PADs), which are overactivated in the inflamed synovium. We characterized the effect of PAD2- and PAD4-induced citrullination on the ability of the plasma-derived serpin C1-inhibitor (C1-INH) to inhibit complement and contact system activation. MethodsCitrullination of the C1-INH was confirmed by ELISA and Western blotting using a biotinylated phenylglyoxal probe. C1-INH-mediated inhibition of complement activation was analyzed by C1-esterase activity assay. Downstream inhibition of complement was studied by C4b deposition on heat-aggregated IgGs by ELISA, using pooled normal human serum as a complement source. Inhibition of the contact system was investigated by chromogenic activity assays for factor XIIa, plasma kallikrein, and factor XIa. In addition, autoantibody reactivity to native and citrullinated C1-INH was measured by ELISA in 101 RA patient samples. ResultsC1-INH was efficiently citrullinated by PAD2 and PAD4. Citrullinated C1-INH was not able to bind the serine protease C1s and inhibit its activity. Citrullination of the C1-INH abrogated its ability to dissociate the C1-complex and thus inhibit complement activation. Consequently, citrullinated C1-INH had a decreased capacity to inhibit C4b deposition via the classical and lectin pathways. The inhibitory effect of C1-INH on the contact system components factor XIIa, plasma kallikrein, and factor XIa was also strongly reduced by citrullination. In RA patient samples, autoantibody binding to PAD2- and PAD4-citrullinated C1-INH was detected. Significantly more binding was observed in anti-citrullinated protein antibody (ACPA)-positive than in ACPA-negative samples. ConclusionCitrullination of the C1-INH by recombinant human PAD2 and PAD4 enzymes impaired its ability to inhibit the complement and contact systems in vitro. Citrullination seems to render C1-INH more immunogenic, and citrullinated C1-INH might thus be an additional target of the autoantibody response observed in RA patients.
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| 6. |
- Laabei, Maisem, et al.
(författare)
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Short leucine-rich proteoglycans modulate complement activity and increase killing of the respiratory pathogen moraxella catarrhalis
- 2018
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Ingår i: Journal of Immunology. - : The American Association of Immunologists. - 0022-1767 .- 1550-6606. ; 201:9, s. 2721-2730
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Tidskriftsartikel (refereegranskat)abstract
- The respiratory pathogen Moraxella catarrhalis is a human-specific commensal that frequently causes acute otitis media in children and stimulates acute exacerbations in chronic obstructive pulmonary disease patients. The exact molecular mechanisms defining host-pathogen interactions promoting pathogenesis are not clearly understood. Limited knowledge hampers vaccine and immunotherapeutic development required to treat this emerging pathogen. In this study, we reveal in detail a novel antibacterial role displayed by short leucine-rich proteoglycans (SLRPs) in concert with complement. We show that fibromodulin (FMOD), osteoadherin (OSAD), and biglycan (BGN) but not decorin (DCN) enhance serum killing of M. catarrhalis. Our results suggest that M. catarrhalis binding to SLRPs is a conserved feature, as the overwhelming majority of clinical and laboratory strains bound all four SLRPs. Furthermore, we resolve the binding mechanism responsible for this interaction and highlight the role of the ubiquitous surface protein (Usp) A2/A2H in mediating binding to host SLRPs. A conserved immune evasive strategy used by M. catarrhalis and other pathogens is the surface acquisition of host complement inhibitors such as C4b-binding protein (C4BP). We observed that FMOD, OSAD, and BGN competitively inhibit binding of C4BP to the surface of M. catarrhalis, resulting in increased C3b/iC3b deposition, membrane attack complex (MAC) formation, and subsequently decreased bacterial survival. Furthermore, both OSAD and BGN promote enhanced neutrophil killing in vitro, both in a complement-dependent and independent fashion. In summary, our results illustrate that SLRPs, FMOD, OSAD, and BGN portray complement-modulating activity enhancing M. catarrhalis killing, defining a new antibacterial role supplied by SLRPs.
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| 7. |
- Trouw, Leendert, et al.
(författare)
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C4b-binding protein and factor h compensate for the loss of membrane-bound complement inhibitors to protect apoptotic cells against excessive complement attack
- 2007
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 282:39, s. 28540-28548
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Tidskriftsartikel (refereegranskat)abstract
- Apoptotic cells have been reported to down- regulate membrane-bound complement regulatory proteins ( m- C- Reg) and to activate complement. Nonetheless, most apoptotic cells do not undergo complement- mediated lysis. Therefore, we hypothesized that fluid phase complement inhibitors would bind to apoptotic cells and compensate functionally for the loss of m- C- Reg. We observed that m- C- Reg are down- regulated rapidly upon apoptosis but that complement activation follows only after a gap of several hours. Coinciding with, but independent from, complement activation, fluid phase complement inhibitors C4b- binding protein ( C4BP) and factorH( fH) bind to the cells. C4BP and fH do not entirely prevent complement activation but strongly limit C3 and C9 deposition. Late apoptotic cells, present in blood of healthy controls and systemic lupus erythematosus patients, are also positive for C4BP and fH. Upon culture, the percentage of late apoptotic cells increases, paralleled by increased C4BP binding. C4BP binds to dead cells mainly via phosphatidylserine, whereas fH binds via multiple interactions with CRP playing no major role for binding of C4BP or fH. In conclusion, during late apoptosis, cells acquire fluid phase complement inhibitors that compensate for the downregulation of m- C- Reg and protect against excessive complement activation and lysis.
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| 8. |
- Kutty Selva, Nandakumar, et al.
(författare)
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A recombinant vaccine effectively induces c5a-specific neutralizing antibodies and prevents arthritis.
- 2010
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Ingår i: PLoS ONE. - San Francisco, CA : Public Library of Science (PLoS). - 1932-6203. ; 5:10
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To develop and validate a recombinant vaccine to attenuate inflammation in arthritis by sustained neutralization of the anaphylatoxin C5a. METHODS: We constructed and expressed fusion protein of C5a and maltose binding protein. Efficacy of specific C5a neutralization was tested using the fusion protein as vaccine in three different arthritis mouse models: collagen induced arthritis (CIA), chronic relapsing CIA and collagen antibody induced arthritis (CAIA). Levels of anti-C5a antibodies and anti-collagen type II were measured by ELISA. C5a neutralization assay was done using a rat basophilic leukemia cell-line transfected with the human C5aR. Complement activity was determined using a hemolytic assay and joint morphology was assessed by histology. RESULTS: Vaccination of mice with MBP-C5a led to significant reduction of arthritis incidence and severity but not anti-collagen antibody synthesis. Histology of the MBP-C5a and control (MBP or PBS) vaccinated mice paws confirmed the vaccination effect. Sera from the vaccinated mice developed C5a-specific neutralizing antibodies, however C5 activation and formation of the membrane attack complex by C5b were not significantly altered. CONCLUSIONS: Exploitation of host immune response to generate sustained C5a neutralizing antibodies without significantly compromising C5/C5b activity is a useful strategy for developing an effective vaccine for antibody mediated and C5a dependent inflammatory diseases. Further developing of such a therapeutic vaccine would be more optimal and cost effective to attenuate inflammation without affecting host immunity.
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| 9. |
- Dieudonné-Vatran, Antoine, et al.
(författare)
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Clinical isolates of Streptococcus pneumoniae bind the complement inhibitor C4b-binding protein in a PspC allele-dependent fashion.
- 2009
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Ingår i: Journal of Immunology. - : The American Association of Immunologists. - 1550-6606 .- 0022-1767. ; 182:12, s. 7865-7877
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Tidskriftsartikel (refereegranskat)abstract
- The complement system constitutes an important component of the innate immune system. To colonize their host and/or to cause disease, many pathogens have evolved strategies to avoid complement-mediated bacterial lysis and opsonophagocytosis. In this study, using a collection of 55 clinical isolates of Streptococcus pneumoniae, we demonstrate for the first time that pneumococci bind the complement inhibitor C4b-binding protein (C4BP). C4BP binding seems to be restricted to certain serotypes such as serotype 4, 6B, 7F, and 14, of which the strains of serotype 14 are the strongest binders. We show that bacteria-bound C4BP retains its functional activity and down-regulates the activation of the classical pathway. Thus, this major respiratory pathogen may escape immune recognition and eradication by the complement system. Furthermore, we show that C4BP binding varies between strains but is dependent on the expression of pneumococcal surface protein C, PspC of group 4. The study of the distribution of group 4 pspC locus shows that most of high-binder serotype 14 isolates harbor an allelic variant of group 4 pspC. Using PspC-negative mutant strains, we identified a new allelic variant of PspC (PspC4.4) as a major ligand for C4BP, revealing a new function for this important pneumococcal virulence factor. Thus pneumococci exploit host C4BP for complement evasion in a PspC allele-dependent manner.
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| 10. |
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