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Fibrillar amyloid beta-protein has been implicated in the pathogenesis of Alzheimer's disease because of its neurotoxicity and its ability to activate complement. Reactive microglia, astrocytes and complement (C') components (reviewed in ref. 6) are associated with senile plaques, the fibrillar, beta-sheet assemblies of amyloid beta-peptide found predominantly in brain from individuals with AD (ref. 7). These indications of inflammatory events are not prevalent in the nonfibrillar "diffuse" plaques often seen in age-matched control cases without dementia. Clinical studies over the past several years have correlated the use of anti-inflammatory drugs with a decrease in the incidence and progression of AD dementia and/or dysfunction, supporting a role for gliosis and inflammation in AD pathogenesis (reviewed in ref. 6). C5a, a product of C' activation, is chemotactic for microglia. Thus, complement activation provides a specific mechanism for recruiting reactive glial cells to the site of the fibrillar amyloid beta-protein plaque, which could lead to inflammatory events, neuronal dysfunction and degeneration. With the use of truncated amyloid beta-peptides, the region of amyloid beta-protein limited by residues 4 and 11 has been identified as critical in the interaction between amyloid beta-protein and C1q, the recognition component of the classical complement pathway (CCP), which results in the activation of C'. Furthermore, substitution of an isoaspartic acid for aspartic acid at amyloid beta-protein residue 7 resulted in the complete elimination of CCP-activating activity. A molecular model of this interaction has been generated that should be useful in the design of candidate therapeutic inhibitors of CCP activation by amyloid beta-protein.
Assuntos
Doença de Alzheimer/metabolismo , Peptídeos beta-Amiloides/química , Peptídeos beta-Amiloides/metabolismo , Ácido Aspártico/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Colágeno/química , Colágeno/metabolismo , Humanos , Modelos Biológicos , Modelos Moleculares , Dados de Sequência Molecular , Fragmentos de Peptídeos/síntese química , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Conformação Proteica , Ratos , Homologia de Sequência de AminoácidosRESUMO
Emergency care systems (ECS) are undergoing a period of rapid development on the African continent. What were formerly large intake zones are now being shaped into dedicated emergency units. Emergency care providers are being trained via certificate and even residency programs. However, significant challenges still exist. Resource limitations, staffing, and other system inputs are often the easiest issues to identify, but they only account for part of the problem. There are other prominent barriers to the delivery of high quality emergency care including lack of governmental leadership, poor system and facility organization, lack of provider training, and community misunderstanding of ECS functions. Released in May 2019, World Health Assembly (WHA) 72 resolution 12.9 "Emergency care systems for universal health coverage: ensuring timely care for the acutely ill and injured" has squarely placed ECS strengthening as a priority item to member state governments. Moving forward, it will be important to ensure that these systems are set up for success, as high-quality emergency care systems have the potential to avert half of all deaths in low- and middle-income countries (LMIC). With momentum building from the recent WHA amendment and the health systems community more focused than ever on the consideration of quality in health systems design, it is of the utmost importance that ECS planners dovetail these interests such that these nascent systems are designed while 1) applying a systems thinking lens and 2) maintaining a focus on quality. This article helps to accomplish this by breaking down ECS into five major categories for evaluation as defined by the WHO Emergency Care Systems Assessment tool, providing an understanding of the functions of each, and identifying which indicators might be used to gauge performance. We also reinforce the notion that these indicators must dive deeper than system inputs and health outcomes, they must be patient centered in order to truly be reflective of success.
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C1, the first component of the classical pathway of complement activation is a complex of three proteins called C1q, C1r and C1s. Normally, C1q binding to aggregated IgG molecules results in activation of the classical pathway of complement. However, C1q has a number of other observed functions, not directly related to complement, that could be mediated by recently identified binding proteins acting as cell-surface receptors or soluble modulators of C1q-mediated functions. This article discusses the various activities of C1q and the evidence that these functions might be influenced by both membrane-bound and soluble C1q-binding proteins.
Assuntos
Complemento C1q/metabolismo , Receptores de Hialuronatos , Glicoproteínas de Membrana , Receptores de Complemento/metabolismo , Animais , Proteínas de Transporte , Membrana Celular/metabolismo , Humanos , Ligantes , Proteínas Mitocondriais , SolubilidadeRESUMO
Glycoprotein adhesion receptors such as selectins contribute to tissue injury in stroke. Ischemic neurons strongly expressed C1q, which may target them for complement-mediated attack or C1qRp-mediated clearance. A hybrid molecule was used to simultaneously inhibit both complement activation and selectin-mediated adhesion. The extracellular domain of soluble complement receptor-1 (sCR1) was sialyl Lewis x glycosylated (sCR1sLex) to inhibit complement activation and endothelial-platelet-leukocyte interactions. sCR1 and sCR1sLex colocalized to ischemic cerebral microvessels and C1q-expressing neurons, inhibited neutrophil and platelet accumulation, and reduced cerebral infarct volumes. Additional benefit was conferred by sialyl Lewis x glycosylation of the unmodified parent sCR1 molecule.
Assuntos
Transtornos Cerebrovasculares/tratamento farmacológico , Ataque Isquêmico Transitório/tratamento farmacológico , Fármacos Neuroprotetores/uso terapêutico , Oligossacarídeos/uso terapêutico , Receptores de Complemento/uso terapêutico , Animais , Plaquetas/fisiologia , Adesão Celular , Córtex Cerebral/irrigação sanguínea , Córtex Cerebral/imunologia , Córtex Cerebral/metabolismo , Infarto Cerebral/tratamento farmacológico , Circulação Cerebrovascular , Transtornos Cerebrovasculares/imunologia , Transtornos Cerebrovasculares/fisiopatologia , Ativação do Complemento , Complemento C1q/metabolismo , Glicosilação , Humanos , Ataque Isquêmico Transitório/imunologia , Ataque Isquêmico Transitório/fisiopatologia , Leucócitos/fisiologia , Camundongos , Neurônios/imunologia , Neurônios/metabolismo , Fármacos Neuroprotetores/administração & dosagem , Fármacos Neuroprotetores/efeitos adversos , Fármacos Neuroprotetores/metabolismo , Neutrófilos/fisiologia , Oligossacarídeos/administração & dosagem , Oligossacarídeos/efeitos adversos , Oligossacarídeos/metabolismo , Adesividade Plaquetária , Receptores de Complemento/administração & dosagem , Receptores de Complemento/metabolismo , Traumatismo por Reperfusão/tratamento farmacológico , Traumatismo por Reperfusão/imunologia , Traumatismo por Reperfusão/metabolismo , Selectinas/metabolismo , Antígeno Sialil Lewis X , Fatores de TempoRESUMO
Rasmussen's encephalitis (RE), a childhood disease characterized by epileptic seizures associated with progressive destruction of a single cerebral hemisphere, is an autoimmune disease in which one of the autoantigens is a glutamate receptor, GluR3. The improvement of some affected children following plasma exchange that removed circulating GluR3 antibodies (anti-GluR3) suggested that anti-GluR3 gained access to the central nervous system where it exerted deleterious effects. Here, we demonstrate that a subset of rabbits immunized with a GluR3 fusion protein develops a neurological disorder mimicking RE. Anti-GluR3 IgG isolated from serum of both ill and healthy GluR3-immunized animals promoted death of cultured cortical cells by a complement-dependent mechanism. IgG immunoreactivity decorated neurons and their processes in neocortex and hippocampus in ill but not in healthy rabbits. Moreover, both IgG and complement membrane attack complex (MAC) immunoreactivity was evident on neurons and their processes in the cortex of a subset of patients with RE. We suggest that access of IgG to epitopes in the central nervous system triggers complement-mediated neuronal damage and contributes to the pathogenesis of both this animal model and RE.
Assuntos
Autoanticorpos/fisiologia , Córtex Cerebral/fisiopatologia , Neurônios/fisiologia , Receptores de Glutamato/imunologia , Animais , Doenças Autoimunes/imunologia , Doenças Autoimunes/patologia , Morte Celular/fisiologia , Córtex Cerebral/patologia , Complexo de Ataque à Membrana do Sistema Complemento/análise , Proteínas do Sistema Complemento/fisiologia , Encefalite/imunologia , Encefalite/patologia , Epilepsia Parcial Complexa/imunologia , Epilepsia Parcial Complexa/patologia , Humanos , Imunização , Imunoglobulina G/análise , Imunoglobulina G/imunologia , Imunoglobulina G/fisiologia , Masculino , Neurônios/imunologia , CoelhosRESUMO
Internalization and infectivity of Trypanosoma cruzi trypomastigotes by macrophages is enhanced by prior treatment of parasites with normal human serum. Heating serum or removing C1q from serum abrogates the enhancement, but augmentation of attachment and infectivity is restored by addition of purified C1q to either serum source. Although both noninfective epimastigotes (Epi) and vertebrate-stage tissue culture trypomastigotes (TCT) bind C1q in saturable fashion at 4 degrees C, internalization by monocytes and macrophages of TCT but not Epi-bearing C1q is enhanced in comparison to untreated parasites. Adherence of human monocytes and macrophages to surfaces coated with C1q also induces a marked enhancement of the internalization of native TCT. C1q enhances attachment of both Epi and TCT to human foreskin fibroblasts, but only when C1q is on the parasite and not when the fibroblasts are plated on C1q-coated surfaces. Only TCT coated with C1q show enhanced invasion into fibroblasts. Although trypomastigotes produce an inhibitor of the complement cascade which limits C3 deposition during incubation in normal human serum, C1q binds to the parasite and enhances entry of trypomastigotes into target cells.
Assuntos
Complemento C1q/fisiologia , Macrófagos/parasitologia , Trypanosoma cruzi/fisiologia , Animais , Sangue , Ativação do Complemento , Complemento C1q/imunologia , Fibroblastos/imunologia , Fibroblastos/parasitologia , Temperatura Alta , Humanos , Macrófagos/imunologia , Monócitos/parasitologia , Trypanosoma cruzi/imunologiaRESUMO
The inflammatory response to intraarticular urate crystals is known to be variable in gouty arthritis. One source of variability may be the modulation of cellular responses by crystal-bound proteins. We have identified three apolipoproteins among the polypeptides bound to urate crystals exposed to plasma. Identification was first based on their coelectrophoresis with polypeptides from isolated lipoproteins and diminution in the protein coat of crystals exposed to lipoprotein-depleted plasma. The apoproteins were immunochemically identified by the Western blotting technique as apoprotein A-I, apoprotein B (apo B), and apoprotein E. Because neutrophils play a central role in acute gout, we investigated the potential effects of lipoproteins on neutrophil-urate crystal interactions. Plasma profoundly inhibited urate crystal-induced neutrophil luminol-dependent chemiluminescence (CL). Lipoprotein depletion by KBr density gradient centrifugation completely abrogated the inhibitory effect of plasma on urate-induced CL. The inhibitory activity of lipoprotein-depleted plasma was restored by adding back the d less than or equal to 1.25 g/cm3 lipoprotein fraction. Plasma also inhibited urate crystal-induced neutrophil superoxide generation and cytolysis (lactic dehydrogenase loss). This inhibition was significantly diminished by lipoprotein depletion, indicating that the lipoprotein effect was not limited to CL. Lipoprotein-depleted plasma reconstituted with very low, intermediate, and low density lipoproteins (LDL) inhibited crystal-induced CL. High density lipoprotein reconstitution was without effect. Immunodepletion from plasma of all apo B lipoproteins by agarose-bound apo B-specific antibody also removed all inhibitory activity for urate-induced CL. Thus, apo B lipoproteins were shown to be the inhibitory species in plasma. Binding of apo B lipoproteins to urate crystals and inhibition of CL was also seen in the absence of other plasma proteins. In addition, the binding of whole lipoprotein particles to the crystals was verified by detection of crystal-associated cholesterol in addition to the apoprotein. The effects of LDL on urate crystal-induced CL were stimulus specific. Coincubation of urate crystals and neutrophils in the presence of 10 micrograms/ml LDL resulted in 83% inhibition. In contrast, CL responses to a chemotactic hexapeptide, opsonized zymosan, and Staphylococcus aureus were not inhibited by LDL. The effects of depletion of apo B lipoproteins on plasma suppression of urate crystal-induced CL appeared to be unique. Plasma or sera depleted of other urate crystal-binding proteins including fibrinogen, fibronectin, C1q, and IgG retained virtually all their CL inhibitory activity. Lipoproteins containing apo B are thus a major regulator of neutrophil responses to urate crystals. These lipoproteins are present in variable concentration in synovial fluid and may exert an important influence on the course of gout.
Assuntos
Apolipoproteínas/sangue , Inflamação/fisiopatologia , Neutrófilos/fisiologia , Ácido Úrico/toxicidade , Anticorpos Monoclonais , Complexo Antígeno-Anticorpo , Apolipoproteínas/isolamento & purificação , Apolipoproteínas B , Eletroforese em Gel de Poliacrilamida , Humanos , Cinética , Lipoproteínas/sangue , Peso Molecular , Neutrófilos/efeitos dos fármacos , Ligação ProteicaRESUMO
Strains of Neisseria gonorrhoeae were used to evaluate bactericidal and opsonic properties of McAb 10 directed against the Neisserial outer membrane antigen, H.8. Gonococci were either serum resistant in the absence but serum sensitive in the presence, of McAb 10, or serum sensitive or serum resistant regardless of the presence of McAb 10. Strain JS3, which fell in the former category, was used in subsequent studies. C1 zymogen formed by reassociation of isolated C1 subunits was not directly activated by JS3 in the presence or absence of C1-inhibitor. JS3 thus was unable to directly activate the classical pathway independently of antibody. When purified classical pathway components were used to deposit C3 on JS3 in the absence of serum regulatory proteins or antibodies, added C1-inhibitor reduced C3 binding to background levels. When McAb 10 was present, C3 binding was unaffected by C1-inhibitor. Covalently bound, large molecular weight C3 alpha-chain-gonococcal complexes were disbanded by methylamine release of ester linkages. Released 125I-C3 migrated as C3b without degradation by gonococcal proteases. Purified classical components alone or McAb 10 alone facilitated JS3 killing by neutrophils; when combined, the two provided maximal killing. Levels of McAb 10 that only slightly increase C3 deposition on JS3 are bactericidal in serum and maximally opsonic in combination with purified classical pathway components.
Assuntos
Anticorpos Monoclonais , Proteínas da Membrana Bacteriana Externa/imunologia , Proteínas Inativadoras do Complemento 1/imunologia , Neisseria gonorrhoeae/imunologia , Atividade Bactericida do Sangue , Complemento C1/imunologia , Via Clássica do Complemento , Humanos , Peso Molecular , Neutrófilos/imunologia , FagocitoseRESUMO
The human mannose-binding protein (MBP) is a multimeric serum protein that is divided into three domains, a cysteine-rich NH2-terminal domain that stabilizes the collagen alpha helix of the second domain and a third COOH-terminal carbohydrate recognition domain. Previous studies have shown that both native and recombinant human MBP bind to wild-type virulent Salmonella montevideo that expresses a mannose-rich lipopolysaccharide. Interaction with MBP results in opsonization and killing by phagocytes. In this report we show that low concentration of MBP (less than 10 micrograms/ml) markedly enhance complement deposition via the alternative complement pathway on S. montevideo. Despite structural similarities between MBP and the C1q subcomponent of the first complement component, MBP did not restore classical pathway activity to C1q-deficient serum, nor did it activate C1s when added to a mixture of C1r and C1s. In the presence of MBP the C3 bound to S. montevideo during incubation in serum was in the form of C3b and iC3b at a ratio of 1:2. Presensitization of S. montevideo with MBP rendered this normally serum resistant organism susceptible to complement-mediated killing. These results emphasize that MBP and complement cooperate in first line defense of the nonimmune host.
Assuntos
Atividade Bactericida do Sangue/efeitos dos fármacos , Proteínas de Transporte/farmacologia , Ativação do Complemento/efeitos dos fármacos , Via Alternativa do Complemento/efeitos dos fármacos , Salmonella , Sequência de Aminoácidos , Complemento C1/imunologia , Complemento C3/metabolismo , Relação Dose-Resposta a Droga , Humanos , Cinética , Lipopolissacarídeos/análise , Mananas/farmacologia , Manose/análise , Lectinas de Ligação a Manose , Dados de Sequência Molecular , Salmonella/efeitos dos fármacos , Salmonella/imunologia , Salmonella/metabolismoRESUMO
Membrane receptors for the soluble 'defense collagens' - naturally occurring chimeric molecules that contain a recognition domain contiguous with a collagen-like triple helical domain and play a role in protecting the host from pathogens entering the blood, lung and other tissues - are being isolated. These receptors are key to understanding the mechanisms by which defense collagens influence cellular responses in order to either provide rapid 'stealth clearance' of cellular debris or to initiate the responses that lead to the destruction of harmful microbes.
Assuntos
Proteínas de Transporte/imunologia , Complemento C1q/imunologia , Glicoproteínas/imunologia , Receptores de Hialuronatos , Glicoproteínas de Membrana , Proteolipídeos/imunologia , Surfactantes Pulmonares/imunologia , Receptores de Superfície Celular/imunologia , Animais , Proteínas de Transporte/metabolismo , Complemento C1q/metabolismo , Glicoproteínas/metabolismo , Humanos , Lectinas de Ligação a Manose , Proteínas de Membrana/imunologia , Proteínas de Membrana/metabolismo , Proteínas Mitocondriais , Proteolipídeos/metabolismo , Proteína D Associada a Surfactante Pulmonar , Proteínas Associadas a Surfactantes Pulmonares , Surfactantes Pulmonares/metabolismo , Receptores de Superfície Celular/metabolismo , Receptores de Complemento/imunologia , Receptores de Complemento/metabolismo , Receptores Imunológicos/imunologia , Receptores Imunológicos/metabolismo , SolubilidadeRESUMO
Biocompatibility is a major concern for developing biomaterials used in medical devices, tissue engineering and drug delivery. Poly(lactic-co-glycolic acid) (PLGA) is one of the most widely used biodegradable materials, yet still triggers a significant foreign body response that impairs healing. Immune cells including macrophages respond to the implanted biomaterial and mediate the host response, which can eventually lead to device failure. Previously in our laboratory, we found that CD200, an immunomodulatory protein, suppressed macrophage inflammatory activation in vitro and reduced local immune cell infiltration around a biomaterial implant. While in our initial study we used polystyrene as a model material, here we investigate the effect of CD200 on PLGA, a commonly used biomaterial with many potential clinical applications. We fabricated PLGA with varied geometries, modified their surfaces with CD200, and examined macrophage cytokine secretion and phagocytosis. We found that CD200 suppressed secretion of the pro-inflammatory cytokine TNF-α and enhanced secretion of the anti-inflammatory cytokine IL-10, suggesting a role for CD200 in promoting wound healing and tissue remodeling. In addition, we found that CD200 increased phagocytosis in both murine macrophages and human monocytes. Together, these data suggest that modification with CD200 leads to a response that simultaneously prevents inflammation and enhances phagocytosis. This immunomodulatory feature may be used as a strategy to mitigate inflammation or deliver drugs or anti-inflammatory agents targeting macrophages.
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Microglial activation has been associated with several degenerative diseases of the central nervous system (CNS). One consequence of activation is the induction of a more efficient phagocytic response, and it is therefore important to determine what factors regulate microglial phagocytosis and whether this capacity influences the progression of neurodegenerative changes. Previous studies have demonstrated that complement component C1q enhances Fc receptor- and CR1-mediated phagocytosis in cells of the myeloid lineage via a cell surface receptor, C1qRp. Because C1q has been found in the area of lesions in several degenerative CNS diseases, the current investigations were carried out to characterize the effects of C1q on microglial phagocytosis. Neonatal rat microglia were shown to express C1qRp, as assessed by flow cytometry and immunocytochemistry. Interaction of these cells with substrate-bound C1q was shown to enhance both FcR-and CR1-mediated phagocytosis two- to fourfold. In addition, introduction of an antibody raised against the carboxy-terminal, cytoplasmic domain of C1qRp into microglia by electroporation markedly diminished the ability of C1q to enhance uptake of IgG-coated targets, whereas nonspecific IgG had no such effect. These results suggest that C1q in areas of active degeneration may promote the phagocytic capacity of microglia via interaction with microglial C1qRp.
Assuntos
Receptores de Hialuronatos , Microglia/fisiologia , Fagocitose , Receptores de Complemento/fisiologia , Animais , Proteínas de Transporte , Células Cultivadas , Enzimas Ativadoras do Complemento/fisiologia , Complemento C1q/fisiologia , Humanos , Glicoproteínas de Membrana/fisiologia , Proteínas Mitocondriais , RatosRESUMO
Complement protein C1q induces the production of superoxide (O2-) by neutrophils via an as yet unidentified receptor or receptor complex. Several strategies were therefore used to identify cell surface molecules involved in the response of neutrophils to C1q and its collagen-like domain (C1q-CLR). Treatment of neutrophils with phosphatidylinositol-specific phospholipase C effectively removed the phosphatidylinositol-linked surface molecules CD14 and CD16, yet did not reduce O2- production in response to C1q. Next, 17 monoclonal antibodies (mAbs) recognizing various neutrophil surface antigens were tested for their ability to inhibit C1q-CLR-mediated O2- production. Only two of the mAbs, 44a and IB4, which recognize CD11b/CD18 (complement receptor 3 or Mac-1), were inhibitory. In addition, neutrophils from a patient with leukocyte adhesion deficiency, which are CD18 deficient, did not produce O2- in response to C1q or C1q-CLR. Because CD11b/CD18 is recognized to play a role in cell adhesion, the role of adherence in C1q-mediated O2- production was explored. Adherence of neutrophils to C1q-CLR-coated surfaces occurred with kinetics, which usually paralleled those of O2- production, and was invariably abolished by the anti-CD11b mAb 44a. However, this mAb often only partially inhibited O2- production, indicating that an avid attachment of neutrophils to the C1q-CLR-coated surface is not required for O2- production.
Assuntos
Antígenos CD/fisiologia , Antígenos CD18/fisiologia , Complemento C1q/farmacologia , Síndrome da Aderência Leucocítica Deficitária/sangue , Neutrófilos/fisiologia , Superóxidos/sangue , Anticorpos Monoclonais/farmacologia , Antígenos CD/imunologia , Antígenos CD11/imunologia , Antígenos CD11/fisiologia , Antígenos CD18/imunologia , Colágeno/farmacologia , Complemento C1q/isolamento & purificação , Complemento C1q/fisiologia , Humanos , Imunoglobulina G/farmacologia , Técnicas In Vitro , Cinética , Síndrome da Aderência Leucocítica Deficitária/imunologia , Neutrófilos/efeitos dos fármacos , Valores de Referência , Fatores de TempoRESUMO
C1q, a subunit of the first component (C1) of the classical complement pathway, binds to neutrophils via its collagen-like region (C1q-CLR) stimulating superoxide production. We previously identified a region of C1q-CLR, defined by fragments generated by trypsin and endoLys-C digestion, that was required for triggering this respiratory burst. To further localize that critical site, purified human C1q was digested with pepsin to generate C1q-CLR, and subsequently cleaved with the matrix metalloproteinases, MMP-1, MMP-2, MMP-3, and MMP-9. Digestion of C1q-CLR with any of these MMPs did not alter the circular dichroism spectra, demonstrating that the fragments generated had maintained the secondary structure observed in the native molecule. All fragments retained the ability to trigger superoxide production by neutrophils. Analysis of the amino acid sequences of the purified cleavage products (none of which are identical to the published cleavage site specificities for these enzymes) demonstrated that it is the C-chain, but not the A-chain of C1q, that is critical for stimulating this activity, and thus may be a target for future therapeutic intervention.
Assuntos
Colagenases/metabolismo , Complemento C1q/metabolismo , Gelatinases/metabolismo , Metaloproteinase 3 da Matriz/metabolismo , Metaloendopeptidases/metabolismo , Neutrófilos/metabolismo , Fragmentos de Peptídeos/metabolismo , Explosão Respiratória , Superóxidos/metabolismo , Sequência de Aminoácidos , Colágeno/química , Complemento C1q/farmacologia , Humanos , Hidrólise , Metaloproteinase 1 da Matriz , Metaloproteinase 2 da Matriz , Metaloproteinase 9 da Matriz , Dados de Sequência Molecular , Neutrófilos/efeitos dos fármacos , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/farmacologia , Estrutura Secundária de Proteína , Estimulação Química , Relação Estrutura-AtividadeRESUMO
C1qR(P) is a type I cell surface glycoprotein that has been shown to enhance ingestion of suboptimally opsonized targets by phagocytes in vitro. In this study, we developed and characterized polyclonal antibodies to study the tissue distribution of this receptor targeted to either the N- or C-terminal portion of the molecule. C1qR(P) was detected in vascular endothelial cells and in a subset of pyramidal neurons in the brain, as well as neutrophils, but it was absent in most tissue macrophages. Analysis of in vitro differentiation of blood monocytes to dendritic cells demonstrated a down-regulation of the receptor as monocytes differentiate to dendritic cells, providing a possible explanation for the lack of reactivity of these cells in tissue. The predominant presence of C1qR(P) in endothelial cells, while compatible with a phagocytic role in host defense and/or clearance of cellular material, suggests other possible novel roles for this receptor.
Assuntos
Endotélio Vascular/química , Receptores de Hialuronatos , Glicoproteínas de Membrana , Receptores de Complemento/análise , Animais , Células CHO , Capilares/citologia , Proteínas de Transporte , Diferenciação Celular , Cricetinae , Cricetulus , Células Dendríticas/química , Células Dendríticas/efeitos dos fármacos , Endotélio Vascular/citologia , Regulação da Expressão Gênica , Humanos , Técnicas Imunoenzimáticas , Macrófagos/química , Macrófagos Peritoneais/química , Camundongos , Microglia/química , Proteínas Mitocondriais , Monócitos/química , Monócitos/citologia , Miocárdio/química , Proteínas de Neoplasias/análise , Proteínas do Tecido Nervoso/análise , Neutrófilos/química , Nucleopoliedrovírus/genética , Especificidade de Órgãos , Fagocitose , Células Piramidais/química , Ratos , Receptores de Complemento/genética , Receptores de Complemento/imunologia , Receptores de Complemento/fisiologia , Proteínas Recombinantes de Fusão/análise , Spodoptera/citologia , Transfecção , Fator de Necrose Tumoral alfa/farmacologia , Células U937/química , Veias Umbilicais/citologia , Vísceras/químicaRESUMO
Human C1qR(P) is a highly glycosylated transmembrane protein that is the human C1q receptor/receptor component that in vitro mediates enhancement of Fc- and C3b-mediated phagocytosis. A human genomic clone and a murine genomic clone that is 73% identical in sequence with the coding region for human C1qR(P) cDNA have been isolated. Chromosomal localization of the human and murine gene demonstrates that these genes are syntenic. Murine cell lines of diverse myeloid origins are shown to respond to interaction of C1q with the enhancement of phagocytosis similar to that seen previously in human peripheral blood monocytes. Northern blot, RT-PCR, Western blot and FACS analyses demonstrated that mC1qR(P) is expressed in these murine myeloid cell lines, but not in a mouse epithelial cell line, similar to the cell type expression of the human gene product. A polyclonal antibody to a peptide sequence common to the deduced sequence from the both murine and human C1qR(P) inhibited the enhancement of phagocytosis response to C1q when cells were permeabilized to permit access of the antibody to the intracellular milieu. These data support the postulate that the identified murine and human genes are homologs, confirm the previously predicted intracellular location of the C-terminus of the molecule, and indicates the necessary role of this intracellular domain in transducing the signal that leads to enhancement of phagocytic function.
Assuntos
Complemento C1q/imunologia , Receptores de Hialuronatos , Glicoproteínas de Membrana/genética , Fagocitose/imunologia , Receptores de Complemento/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Proteínas de Transporte , Linhagem Celular , Mapeamento Cromossômico , DNA Complementar , Citometria de Fluxo/métodos , Perfilação da Expressão Gênica , Humanos , Glicoproteínas de Membrana/imunologia , Camundongos , Microscopia de Fluorescência/métodos , Proteínas Mitocondriais , Dados de Sequência Molecular , RNA Mensageiro , Coelhos , Receptores de Complemento/imunologia , Ovinos , Células U937RESUMO
The complement system is a critical element of the innate immune system recognizing and killing, or targeting for destruction, otherwise pathogenic organisms. In addition to triggering the generation of a membranolytic complex, complement proteins interact with cell surface receptors to promote a local inflammatory response that contributes to the protection and healing of the host. Compelling evidence has been reported that in Alzheimer's Disease complement activation occurs in the brain, and that this contributes to the development of a local inflammatory state that is correlated with cognitive dysfunction. However, recent data suggest that at least some of the complement components have the ability to contribute to neuroprotective pathways. Thus, it is the balance of these seemingly competing events that influences the ultimate state of neuronal function. Knowledge of the unique molecular interactions that occur in the development of Alzheimer's Disease, the functional consequences of those interactions, and the proportional contribution of each element to this disorder, should facilitate the design of effective therapeutic strategies for this disease.
Assuntos
Doença de Alzheimer/patologia , Proteínas do Sistema Complemento/fisiologia , Doença de Alzheimer/prevenção & controle , Transtornos Cognitivos/patologia , Ativação do Complemento/efeitos dos fármacos , Ativação do Complemento/fisiologia , HumanosRESUMO
As the brain ages, amyloid deposits accumulate and, as these deposits condense into a beta-sheet conformation, they contribute to the organization of cellular responses and maintain a chronic level of stimulation and injury. Furthermore, accompanying reactions can lead to the production of additional beta-amyloid, the build up of additional fibrillar beta-amyloid, and prolongation of the response. As it accumulates, beta-amyloid appears to develop properties that drive many signal transduction processes in the classic injury cascade and also activate complement, which results in an amplified beta-amyloid AD cascade. In this way several mechanisms, although apparently independent, proceed in parallel, reinforce each other, and perpetuate pathology and structural damage to the brain. Specifically, we suggest that via the activation of complement, initiation, and perpetuation of other cascades, and its own direct toxic actions, beta-amyloid converts an acute response to injury into a chronic damaging inflammatory reaction thereby contributing to neuronal dysfunction and degeneration.
Assuntos
Reação de Fase Aguda/patologia , Peptídeos beta-Amiloides/fisiologia , Lesões Encefálicas/patologia , Reação de Fase Aguda/metabolismo , Animais , Lesões Encefálicas/metabolismo , Doença Crônica , Ativação do Complemento/fisiologia , HumanosRESUMO
In transgenic models of Alzheimer's disease (AD) neuronal loss has not been widely observed. The loss of neurons in AD may be due to chronic activation of complement (C') by beta-amyloid (A beta). A beta has been shown to activate C' by binding to a site on the C1q A-chain. The mouse A-chain sequence differs significantly from human, and a peptide based on the mouse A-chain sequence was ineffective at blocking activation of C' by A beta in contrast to the inhibition seen with the human peptide. Comparison of mouse and human serum showed that human C' was activated more effectively by A beta than was mouse C'. Therefore, additional genetic manipulations may be necessary to replicate in the murine model the inflammation and neurodegeneration that occur in AD.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Ativação do Complemento/fisiologia , Complemento C1q/genética , Doença de Alzheimer/imunologia , Doença de Alzheimer/metabolismo , Sequência de Aminoácidos , Peptídeos beta-Amiloides/imunologia , Peptídeos beta-Amiloides/farmacologia , Animais , Sítios de Ligação/fisiologia , Ativação do Complemento/efeitos dos fármacos , Complemento C1q/química , Complemento C1q/farmacologia , Relação Dose-Resposta a Droga , Humanos , Imunoglobulina G/metabolismo , Imunoglobulina G/farmacologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Modelos Moleculares , Degeneração Neural/imunologia , Degeneração Neural/metabolismo , Fragmentos de Peptídeos/farmacologia , Estrutura Quaternária de Proteína , Especificidade da EspécieRESUMO
Recent reports that complement proteins comprising the classical pathway are associated with senile plaques suggest that activation of the classical complement cascade in Alzheimer's disease tissue results in bystander cell lysis and may contribute to AD neuropathology. Analysis of cerebrospinal fluid may prove to be a useful means of detecting changes in immunological activity in the brain. We use an enzyme-linked immunosorbent assay to measure levels of C1q, a subunit of the classical complement cascade, in the CSF of patients clinically diagnosed with possible or probable AD. Significantly lower levels of C1q were detected in the CSF of the Alzheimer group as compared to control CSF [AD: mu = 268 ng/ml, SD = 84; non-AD: mu = 340 ng/ml, SD = 76; F(1, 44) = 5.84, p = 0.02]. Diminished performance on global measures of mental status such as the Mini-Mental State Exam (R = 0.45; p = 0.0072) and Blessed's Information, Memory, and Concentration test (R = 0.42; p = 0.0138) showed high correlations with decreased C1q levels. More specific measures of cognitive function, such as word recall (R = 0.42; p = 0.012), word recognition (R = 0.52; p = 0.0017) and delayed recall (R = 0.45; p = 0.0062) memory tasks also correlated strongly with decreased C1q levels.