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PubMed1984

[Serum immunoglobulins and complement fractions in protein malnutrition].

Serum immunoglobulins and some complement components (C1q, C3c, C4, factor B, C9) have been evaluated in 99 malnourished patients. The sole abnormality which seems related to protein calorie malnutrition is a C1q decrease significantly correlated to serum albumin, thyroxin binding prealbumin and retinol binding protein. The immunoglobulins modifications seem to be related to pathological conditions associated with malnutrition (sepsis, liver diseases).

Adult↗
PubMed1992

Complement gene expression in human brain: comparison between normal and Alzheimer disease cases.

Many investigators have reported the presence of complement proteins in Alzheimer disease (AD) brains, but their origin is uncertain. We report the expression of complement genes C1q, C3 and C4 in RNA extracted from temporal cortex samples of post-mortem human brain. The transcripts for C3 and C4 were detected by Northern hybridization analysis, and the mRNAs for C1q, C3 and C4 were detected by polymerase chain reaction (PCR) amplification of brain derived complementary DNA (cDNA). The relative abundances of mRNAs for C3 and C4 were compared between samples of temporal cortex from neurologically normal and Alzheimer disease (AD) cases, using a semiquantitative PCR assay. There was a 3.01 fold mean increase in expression of C3 and a 3.27-fold mean increase in expression of C4 in AD samples compared to control cases. These results indicate that localized synthesis of some of the major complement components can occur in human brain. The factors causing activation of complement in AD still remain undetermined.

Aged↗
PubMed2004

Reduced anti-TNFalpha autoantibody levels coincide with flare in systemic lupus erythematosus.

Deviating cytokine patterns, as a consequence of aberrant immunoregulation, is implicated to be of aetiopathogenetic importance in systemic lupus erythematosus (SLE). To evaluate the possibility of anti-cytokine autoantibody-mediated cytokine regulation/dysregulation, IgG class autoantibodies against cytokines (IL-1beta, IL-6, IL-10, TNFalpha and TGFbeta(1)) were analysed by enzyme-linked immunosorbent assay (ELISA) in serial serum samples from clinically well-characterized SLE patients and in normal human sera (NHS). Anti-TNFalpha autoantibody levels were lower in patients with active disease compared to inactive disease (P<0.001) as well as to NHS (P<0.001). The anti-TNFalpha antibody levels correlated inversely to the SLE disease activity index (SLEDAI) (r(2)=0.07, P<0.01), whereas anti-TGFbeta antibodies were raised in SLE and correlated positively to levels of complement factor C1q (r(2)=0.08, P<0.005). Generally raised anti-cytokine antibody levels and correlations to disease activity measures were found in one individual. Inverse correlations were found comparing SLEDAI scores and autoantibodies to TNFalpha (r(2)=0.92) and IL-6 (r(2)=0.86) and positive correlations were found between levels of anti-TNFalpha and C1q (r(2)=0.86) and C3 (r(2)=0.90). We show, for the first time, a coincidence between reduced anti-TNFalpha autoantibody levels and disease exacerbation in SLE, which is of interest regarding aetiopathogenesis and disease control.

Adolescent↗
PubMed1977

Separation of hydroxyproline-containing protein from C1q (a subcomponent of complement) in serum.

Precipitation of the euglobulin fraction from serum separates C1q from another hydroxyproline-containing protein(s), which remains in the serum-minus-euglobulin fraction. The presence of C1q in the euglobulin fraction has been verified by radial immunodiffusion assay, by sensitivity to collagenase, by hydroxyproline content, and by electrofocusing. The presence of another hydroxyproline-containing protein(s) in the serum-minus-euglobulin fraction has been verified by the same criteria. The isoelectric pH range of C1q is 6.1-7.0; the isoelectric pH range of the other hydroxyproline-containing protein(s) is 4.2-5.5.

Blood Protein Electrophoresis↗
PubMed2005

Characterization of Haemonchus contortus calreticulin suggests its role in feeding and immune evasion by the parasite.

Haemonchus contortus, a gastrointestinal parasite of sheep and goat feeds on the blood of its host and causes bleeding at the biting site. In this report, we demonstrate that the Ca2+ binding protein, calreticulin (CalR), is present in excretory/secretory products of adult worms. The secreted CalR enhanced plasma coagulation time. Using recombinant fragments, this property has been mapped to C-terminal part of the molecule which has binding sites for Ca2+ as well as clotting factors. Complement protein C1q bound to immobilized CalR and C1q dependent lysis of sensitized sheep erythrocytes was inhibited by CalR, a function mapped to N-domain of the protein. Factor X and a 24 kDa polypeptide derived from prothrombin but not prothrombin bound to immobilized CalR. The binding site for 24 kDa polypeptide in the CalR molecule has been localized in the P-domain. Our results suggest at least two functions for secreted CalR: first, to prevent blood clotting by binding to Ca2+ and clotting factors thus enabling parasite to feed on the host blood and second to modulate the host immune response by binding to complement C1q thereby facilitating parasite's survival within the host.

Amino Acid Sequence↗
PubMed1989

Complement components in Nigerians with bronchial asthma.

Serum complement components C1q, C3, C4, factor B, and C3d breakdown products were measured in asthmatic Nigerians and in age-matched and sex-matched controls. C3 mean level was higher than in controls while C1q and C4 mean levels were lower than in controls. High levels of C3d in asthmatic patients suggest the possible role of C3a and C5a anaphylatoxins in the etiopathogenesis of perennial asthma in Nigerian patients in a tropical environment with ubiquitous airborne allergens and infective agents. The significantly elevated levels of IgM and IgG may suggest recurrent respiratory challenge of perennial antigens in our environment.

Adult↗
PubMedDate not supplied

Comprehensive evaluation of complement components in the course of type I (Lepra) and type II (ENL) reactions.

Complement components C1q and C4 of classic pathway; C3d, a breakdown product of C3, and factor B of alternate pathway: and C3, a component both of classic and alternate pathways, were studied in 35 patients, comprising 18 type I (Lepra) and 17 type II (ENL) reactions. There was a significant decrease in C3 and factor B with a concomitant rise of C3d during ENL. These changes indicate their preeminent role in immunogenesis of type II (ENL) reaction. The changes in the classic pathway components, on the other hand, were insignificant, apparently suggesting its limited involvement in ENL. Furthermore, reversion of factor B and C3d after subsidence of reaction is intriguing and may indicate that they are not substantially affected even with contemporary treatment. Complement components, of both classic and alternate pathways, showed no significant alterations either during type I (Lepra) reaction or after its amelioration.

Complement Activating Enzymes↗
PubMed1998

Bullous systemic lupus erythematosus: detection of antibodies against noncollagenous domain of type VII collagen.

A 9-year-old girl with systemic lupus erythematosus developed bullous eruption. Histopathologic examination showed subepidermal blistering and immunoglobulins (IgG, IgM, IgA) and complement components (C1q, C3) deposited linearly at the basement membrane zone. IgG in this patient's serum bound to the dermal side of 1 mol/L sodium chloride-split normal human skin, and a 290 kd protein was identified in the dermal extract. The patient's serum recognized various epitopes on the noncollagenous domain as demonstrated by the use of fusion proteins of type VII collagen. Resolution of the bullous eruption occurred after treatment with dapsone.

Antimetabolites↗
PubMed1985

Application of molecular cloning to studies on the complement system.

The isolation of cDNA and, in certain cases, genomic clones has been reported for the following complement proteins: C1q, C2, C3, C4, C5, C9, and factor B, C4b-binding protein and C1-inhibitor. The availability of cloned DNA has allowed rapid advances to be made in the understanding of the structure (from the derived amino acid sequences), function, biosynthesis and genetics of these proteins. This is most strongly illustrated from recent studies on the C2, factor B and C4 genes, which code for the class III molecules of the major histocompatibility complex, especially as certain allelic forms of these genes may be associated with disease susceptibility.

Animals↗
PubMed2005

Add Alzheimer's disease to the list of autoimmune diseases.

A sole pathological event leading to Alzheimer's disease (AD) remains undiscovered in spite of decades of costly research. In fact, it is more probable that the causes of AD are the result of a myriad of intertwining pathologies. However, hope remains that a single awry event could lead to the many pathological events observed in AD brain tissues thereby creating the presentation of simultaneous pathologies. Age-related vascular diseases, which include an impaired blood-brain barrier (BBB), are a common denominator associated with various degrees of dementia, including AD. Recently, a key finding not only demonstrated the anomalous presence of immunoglobulin (Ig) detection in the brain parenchyma of AD tissues but, most importantly, specific neurons that showed degenerative, apoptotic features contained these vascular-derived antibodies. In addition, subsequent studies detected classical complement components, C1q and C5b-9, in these Ig-positive neurons, which also were spatially more associated with reactive microglia over the Ig-negative neurons. Thus, it is possible that the mere presence of anti-neuronal autoantibodies in the serum, whose importance had been previously dismissed, may be without pathological consequence until there is a BBB dysfunction to allow the deleterious effects of these autoantibodies access on their targets. Hence, these observations suggest autoimmunity-induced cell death in AD.

Aged↗
PubMed2000

Mannan-binding lectin and C1q bind to distinct structures and exert differential effects on macrophages.

While the interaction of complement component C1q with cellular proteins is extensively studied, much less is known about the binding of the structurally related molecule, mannan-binding lectin (MBL) to various cells. Here we show by cytofluorimetry that the interaction of MBL with immunocompetent cells is much more restricted than that of C1q. It is shown that under conditions of physiological ionic strength MBL binds to human monocyte-derived macrophages (Mphi) and monocytoid cell lines, but not to T and B lymphocytes, in contrast to C1q, which interacts with all these cells under the same conditions. As opposed to the binding of C1q, low ionic strength does not improve the interaction of MBL with Mphi. No competition for cellular binding sites was found when MBL and C1q were added simultaneously to the cells. Studying the functional consequences of the interaction, we found that the release of TNF-alpha from Mphi is induced by C1q but not by MBL. Production of complement C3 by Mphi is stimulated by C1q strongly, while the effect of MBL is much weaker. C3 produced upon C1q-mediated triggering is shown to opsonize RBC, resulting in enhanced phagocytosis. These results suggest that cell membrane molecules binding MBL and C1 q are not identical; moreover, biological functions exerted by these proteins are also markedly different.

Binding Sites↗
PubMed1997

C1Q synthesis by tissue mononuclear phagocytes from normal and from damaged rat liver: up-regulation by dexamethasone, down-regulation by interferon gamma, and lipopolysaccharide.

The subcomponent of complement C1, C1q, mediates complement activation via the classical pathway, and therefore may play an important role in the inflammatory processes in which complement activation is involved. The aim of our study was to investigate C1q synthesis by macrophages of normal and of acutely damaged livers. The localization of C1q in liver tissue was studied by immunohistochemistry. Rat liver tissue macrophages were isolated from normal as well as from acutely damaged (carbon tetrachloride model) liver, and were separated into small, monocyte-like phagocytes and large, mature tissue macrophages, as revealed by immunocytochemistry. C1q gene expression was studied by endogeneous labeling of newly synthesized proteins, immunoprecipitation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and by reverse-transcription polymerase chain reaction (RT-PCR) of C1qB messenger RNA (mRNA). Semiquantitative analysis was performed by Northern blotting of total RNA and hybridization with the radioactively labeled RT-PCR product. C1 esterase inhibitor synthesis was studied in parallel. For comparison, C1q and C1-inhibitor synthesis were also investigated in blood monocytes and peritoneal macrophages. C1q was weakly detectable in sinusoidal cells of the normal liver. C1qB mRNA, as well as constitutive synthesis and secretion of C1q, was clearly detected in freshly isolated and cultured Kupffer cells from normal rat liver. In comparison, newly recruited "inflammatory" macrophages from damaged rat liver synthesized considerably lower amounts of the protein, similar to what was found in the monocyte-like macrophages of normal liver and in peritoneal macrophages. Monocyte C1qB mRNA was not detected even by RT-PCR, and remained undetectable during the time in culture. Similar behavior was observed for C1-inhibitor synthesis. Treatment of the cultures with interferon gamma (IFN-gamma) or lipopolysaccharide (LPS) strongly decreased, whereas treatment with dexamethasone strongly increased C1q gene expression in the macrophage populations, and induced C1qB mRNA in cultured monocytes, as revealed by RT-PCR. Kupffer cells of normal liver may produce considerable amounts of C1q, whereas the inflammatory macrophages of the acutely damaged liver may not be so important for the synthesis of C1q.

Animals↗
PubMed1996

Transplantation with allogenic bone marrow from a donor with systemic lupus erythematosus (SLE): successful outcome in the recipient and induction of an SLE flare in the donor.

OBJECTIVE: To investigate the transfer of autoimmunity by allogenic bone marrow transplantation. METHODS: Bone marrow transplantation was performed in a 43 years old man with acute myeloid leukaemia (AML) in remission. The donor was his HLA identical brother who had a mild systemic lupus erythematosus (SLE). Autoantibodies, including antinuclear, anti-C1q, and anticardiolipin antibodies, were measured before and after transplantation. RESULTS: Transient mild graft versus host disease (GvHD) developed in the recipient in the weeks following transplantation. The donor had persistently high concentrations of anti-C1q antibodies to the collagenous region of the complement component C1q. Three months after transplantation the recipient developed antiC1q antibodies that persisted for two months. No other autoantibodies and no SLE-like manifestations appeared. Chronic GVHD started five months posttransplant and responded to intensified immunosuppressive treatment. Three years post-transplant the patient was in unmaintained remission. Within a few weeks after bone marrow donation the donor's disease was exacerbated with development of severe pulmonary alveolitis which required treatment with cyclophosphamide. CONCLUSIONS: When bone marrow transplantation was performed in a patient with AML with bone marrow from an HLA identical brother who had SLE, no evidence of transfer of disease was obtained. However, the recipient temporarily produced anti-C1q antibodies which was a characteristic feature of the donor's SLE and was probably produced by the transplant. The flare of the donor's SLE might be related to the bone marrow tap.

Adult↗
PubMed2004

Origin of the classical complement pathway: Lamprey orthologue of mammalian C1q acts as a lectin.

The lectin complement pathway in innate immunity is closely related to the classical complement pathway in adaptive immunity, with respect to the structures and functions of their components. Both pathways are initiated by complexes consisting of collagenous proteins and serine proteases of the mannose-binding lectin (MBL)-associated serine protease (MASP)/C1r/C1s family. It has been speculated that the classical pathway emerged after the lectin pathway, and that the activation mechanism of the latter was partially conserved. The classical and lectin pathways can be traced back to at least cartilaginous fish and ascidian (urochordata), respectively. To elucidate the evolution of the complement system, we isolated and characterized a GlcNAc-binding lectin from sera of lamprey (agnathans), the most primitive vertebrate that lacks the classical pathway. Lamprey GlcNAc-binding lectin was an oligomer consisting of 24-kDa subunits. cDNA and phylogenetic analyses revealed that the lamprey GlcNAc-binding lectin is an orthologue of mammalian C1q, a collagenous subcomponent of the first component involved in binding to immunoglobulins in the classical pathway. Lamprey C1q copurified with MASP-A, a serine protease of the MASP/C1r/C1s family, which exhibited proteolytic activity against lamprey C3. Surface plasmon resonance analysis showed that lamprey C1q specifically bound to GlcNAc, but not various other carbohydrates tested. These results suggest that C1q may have emerged as a lectin and may have functioned as an initial recognition molecule of the complement system in innate immunity before the establishment of adaptive immunity such as immunoglobulins in the cartilaginous fish.

Amino Acid Sequence↗
PubMed1981

Quantitative studies of the interaction of 3H-dsDNA/anti-DNA immune complexes with complement: comparison and evaluation of the Raji cell, the solution phase C1Q, and the red blood cell linked complement fixation radioimmunoassays.

We have prepared antibody/3H-dsDNA immune complexes and have used three independent radioimmunoassays to quantitate their interaction with complement; the solution phase C1q assay, the Raji cell assay, and a complement-based red blood cell adherence assay (RBC-CF). Our results indicate that although there is reasonable qualitative agreement between the Raji cell assay and the RBC-CF assay, there are some differences in the quantitative range of sensitivities of the two assays. On the other hand, we find that most of the complement-fixing antibody/3H-dsDNA complexes are not detected in the solution phase C1q assay. The results suggest this is because the absolute concentrations of the immune complexes were too low to achieve significant precipitation under the standard conditions used in the C1q assay. The implication of these findings with respect to the potential detection and analysis of antibody/dsDNA immune complexes is discussed.

Antibodies↗
PubMed2004

Maturation of dendritic cells abrogates C1q production in vivo and in vitro.

Dendritic cells (DCs) and complement are essential components of the innate immune system. Immature DCs (immDCs) and mature DCs (mDCs) can migrate to lymphoid areas inducing, respectively, tolerance and immune responses. Primary deficiency of complement component C1q (C1q) leads to autoimmunity, suggesting a role in the maintenance of tolerance. In the present study, we investigated the production of C1q by immDCs, mDCs, and macrophages. We demonstrated that monocyte-derived and CD34(+)-derived interstitial DCs are a rich source of C1q. C1q produced by immDCs is functionally active in complement activation and binding to apoptotic cells. The production of C1q is completely down-regulated upon DC maturation in vitro. Moreover, we found that DC differentiation in the presence of interferon-alpha (IFN-alpha) accelerated DC maturation and strongly impaired overall C1q production. Finally, we demonstrated the presence, in significant numbers, of DC-SIGN(+)/C1q(+) cells in T-cell areas of tonsils, next to DC-LAMP(+) mDCs lacking C1q. We conclude from these results that immDC, a cell with tolerogenic properties, is a rich source of active C1q in vitro and in vivo, which is down-regulated on maturation. Therefore, immDCs may be considered an additional source of C1q in humans.

Cell Differentiation↗