C1q-deficient Mice Research Articles

Nonencapsulated Streptococcus pneumoniae cause Bacteremia through Inhibition of C-Reactive Protein Binding

Abstract Naturally occurring nonecapsulated Streptococcus pneumoniae (NESp) are found worldwide and can cause invasive infections. In contrast, encapsulated pneumococci that fail to express capsule are rapidly cleared from the blood of infected mice. We previously demonstrated that NESp expressing the Ami-like proteins AliC and AliD are able to evade complement-mediated killing. Data indicated that factor H (FH) failed to bind to NESp, and thus did not reduce complement activation as seen in FH binding pneumococci. Proteomic data have shown that deletion of aliC and aliD altered pneumococcal protein expression. Additionally, NESp expressing AliC and AliD caused invasive pneumococcal disease in C1q-deficient mice. The purpose of this study was to examine the regulated pneumococcal genes in complement evasion by NESp. Flow cytometry was used to examine binding of C3b to NESp. A mouse model of infection was used to investigate complement interaction with NESp in vivo. NESp expressing AliC and AliD were able to persist for at least four days following intravenous infection of mice. Deletion of aliC and aliD resulted in the clearance of NESp within 24 hours post-infection. There was a four-fold increase in C3b deposition on the mutant NESp compared to the wildtype. Choline binding protein AC (CbpAC), a variant of pneumococcal protein A (PspA), was found to have reduced expression in the aliC and aliD deleted mutant. C-reactive protein (CRP) showed increased binding to NESp in which cbpAC was deleted. Regulated expression of CbpAC in NESp is able to overcome the innate immune response and lead to persistence of NESp within the host by reducing C1q deposition and arresting classical complement activation. Supported by Departmental research funds.

Complement protein C1q activates lung fibroblasts and exacerbates silica-induced pulmonary fibrosis in mice

Pulmonary fibrosis is a progressive fibrotic disease with a poor prognosis and has suboptimal therapeutic options. The complement protein, C1q, which has various functions, such as promoting phagocytosis and signal transduction, has been shown to exacerbate several fibrosis-related diseases such as myofibrosis. In this study, we examined the role and cellular targets of C1q in pulmonary fibrosis. Silica-induced pulmonary fibrotic C1q-deficient mice showed improvement in fibrosis, and intratracheal administration of C1q to normal mice led to the induction of fibrotic changes. Single-cell RNA sequencing analysis revealed the early activation of fibroblasts and type 2 alveolar epithelial cells after intratracheal administration of C1q, and treatment of primary lung fibroblasts with C1q induced the expression of profibrotic genes. Thus, the inhibition of C1q may be regarded as a therapeutic target for pulmonary fibrosis.

Novel Monoclonal Antibodies Against Mouse C1q: Characterisation and Development of a Quantitative ELISA for Mouse C1q

Recent studies have identified roles for complement in synaptic pruning, both physiological during development and pathological in Alzheimer’s disease (AD). These reports suggest that C1q initiates complement activation on synapses and C3 fragments then tag them for removal by microglia. There is an urgent need to characterise these processes in rodent AD models; this requires the development of reagents and methods for detection and quantification of rodent C1q in fluids and pathological tissues. These will enable better evaluation of the role of C1q in disease and its value as disease biomarker. We describe the generation in C1q-deficient mice of novel monoclonal antibodies against mouse and rat C1q that enabled development of a sensitive, specific, and quantitative ELISA for mouse and rat C1q capable of measuring C1q in biological fluids and tissue extracts. Serum C1q levels were measured in wild-type (WT), C1q knockout (KO), C3 KO, C7 KO, Crry KO, and 3xTg and APPNL-G-F AD model mice through ageing. C1q levels significantly decreased in WT, APPNL-G-F, and C7 KO mice with ageing. C1q levels were reduced in APPNL-G-F compared to WT at all ages and in 3xTg at 12 months; C3 KO and C7 KO, but not Crry KO mice, also demonstrated significantly lower C1q levels compared to matched WT. In brain homogenates, C1q levels increased with age in both WT and APPNL-G-F mice. This robust and adaptable assay for quantification of mouse and rat C1q provides a vital tool for investigating the expression of C1q in rodent models of AD and other complement-driven pathologies.

Complement C1q Enhances Primary Hemostasis.

The cross-talk between the inflammatory complement system and hemostasis is becoming increasingly recognized. The interaction between complement C1q, initiation molecule of the classical pathway, and von Willebrand factor (vWF), initiator molecule of primary hemostasis, has been shown to induce platelet rolling and adhesion in vitro. As vWF disorders result in prolonged bleeding, a lack of C1q as binding partner for vWF might also lead to an impaired hemostasis. Therefore, this study aimed to investigate the in vivo relevance of C1q-dependent binding of vWF in hemostasis. For this purpose, we analyzed parameters of primary and secondary hemostasis and performed bleeding experiments in wild type (WT) and C1q-deficient (C1qa−/−) mice, with reconstitution experiments of C1q in the latter. Bleeding tendency was examined by quantification of bleeding time and blood loss. First, we found that complete blood counts and plasma vWF levels do not differ between C1qa−/− mice and WT mice. Moreover, platelet aggregation tests indicated that the platelets of both strains of mice are functional. Second, while the prothrombin time was comparable between both groups, the activated partial thromboplastin time was shorter in C1qa−/− mice. In contrast, tail bleeding times of C1qa−/− mice were prolonged accompanied by an increased blood loss. Upon reconstitution of C1qa−/− mice with C1q, parameters of increased bleeding could be reversed. In conclusion, our data indicate that C1q, a molecule of the first-line of immune defense, actively participates in primary hemostasis by promoting arrest of bleeding. This observation might be of relevance for the understanding of thromboembolic complications in inflammatory disorders, where excess of C1q deposition is observed.

Nonencapsulated Streptococcus pneumoniae causes Bacteremia in C1q-Deficient Mice

Abstract Since the introduction of the pneumococcal conjugate vaccines, the frequency of infections by nonencapsulated Streptococcus pneumoniae (NESp) has steadily increased. We previously demonstrated that NESp expressing AliC and AliD instead of the canonical capsule synthesis genes in the cps locus are able to survive killing in a whole blood bactericidal assay. Also, NESp expressing AliC and AliD are associated with invasive pneumococcal disease (IPD). The purpose of this study was to determine if NESp expressing AliC and AliD evade complement-mediated killing. Flow cytometry was used to examine binding of C3b and factor H (FH) to NESp in vitro. We used a chinchilla model of otitis media (OM) and mouse models of infection to examine complement interaction with NESp in vivo. Deletion of aliC and aliD resulted in reduced expression of choline binding protein AC (CbpAC), a variant of pneumococcal surface protein C (PspC). There was a four-fold increase in C3b deposition on a CbpAC mutant compared to the wild-type. Deletion of cbpA significantly reduced virulence in OM in which complement is known to play a role. When C1q-deficient mice were intravenously challenged with the wild-type strain, 60% of the mice failed to survive compared to 100% survival of mice challenged with the CbpA deficient mutant. Further, the wild-type NESp burden in the blood of C1q-deficient mice reached 1×107CFU/ml, and bacteremia persisted for at least five days. In contrast, the CbpAC mutant was not detectable in the blood by 48 hours post-infection. Overall, the ratio of CbpA and deposited C3b on the NESp surface appears to be crucial for NESp to counteract complement deposition and evade host response. Thus, NESp are able to initiate bacteremia and persist within the host.

MafB is a critical regulator of complement component C1q

The transcription factor MafB is expressed by monocytes and macrophages. Efferocytosis (apoptotic cell uptake) by macrophages is important for inhibiting the development of autoimmune diseases, and is greatly reduced in Mafb-deficient macrophages. Here, we show the expression of the first protein in the classical complement pathway C1q is important for mediating efferocytosis and is reduced in Mafb-deficient macrophages. The efferocytosis defect in Mafb-deficient macrophages can be rescued by adding serum from wild-type mice, but not by adding serum from C1q-deficient mice. By hemolysis assay we also show that activation of the classical complement pathway is decreased in Mafb-deficient mice. In addition, MafB overexpression induces C1q-dependent gene expression and signals that induce C1q genes are less effective in the absence of MafB. We also show that Mafb-deficiency can increase glomerular autoimmunity, including anti-nuclear antibody deposition. These results show that MafB is an important regulator of C1q.

The non-inflammatory role of C1q during Her2/neu-driven mammary carcinogenesis

ABSTRACTThere is an ever increasing amount of evidence to support the hypothesis that complement C1q, the first component of the classical complement pathway, is involved in the regulation of cancer growth, in addition to its role in fighting infections. It has been demonstrated that C1q is expressed in the microenvironment of various types of human tumors, including breast adenocarcinomas. This study compares carcinogenesis progression in C1q deficient (neuT-C1KO) and C1q competent neuT mice in order to investigate the role of C1q in mammary carcinogenesis. Significantly accelerated autochthonous neu+ carcinoma progression was paralleled by accelerated spontaneous lung metastases occurrence in C1q deficient mice. Surprisingly, this effect was not caused by differences in the tumor-infiltrating cells or in the activation of the complement classical pathway, since neuT-C1KO mice did not display a reduction in C3 fragment deposition at the tumor site. By contrast, a significant higher number of intratumor blood vessels and a decrease in the activation of the tumor suppressor WW domain containing oxidoreductase (WWOX) were observed in tumors from neuT-C1KO as compare with neuT mice. In parallel, an increase in Her2/neu expression was observed on the membrane of tumor cells. Taken together, our findings suggest that C1q plays a direct role both on halting tumor angiogenesis and on inducing apoptosis in mammary cancer cells by coordinating the signal transduction pathways linked to WWOX and, furthermore, highlight the role of C1q in mammary tumor immune surveillance regardless of complement system activation.

Complement component C1q limits osteoarthritis pathology by regulating macrophage activation

Abstract Osteoarthritis (OA), the most common form of arthritis in the world, is characterized by articular cartilage breakdown in synovial joints. There is evidence of low-grade inflammatory responses in OA, but their contribution to OA pathogenesis is unclear. Studies have demonstrated that dysregulated complement activity is involved in OA pathogenesis. The complement component, C1q, is known to regulate inflammation via mechanisms involving apoptotic cell clearance and macrophage activation. Thus, we hypothesized that C1q is a key negative regulator of inflammatory mechanisms in OA. Using a combination of NanoString-based mRNA quantification and Luminex-based analyses for cytokine profiling, we found that differentiation of human monocyte-derived macrophages in C1q-depleted serum followed by stimulation with cartilage debris resulted in enhanced pro-inflammatory (e.g., IL1β) and reduced anti-inflammatory (e.g,. IL10) cytokine expression and secretion compared to cells grown in normal human serum. To definitively establish a regulatory role for C1q in OA, we used a well-established destabilization of the medial meniscus (DMM) model of knee OA in genetically-deficient mice. We found that knees of C1q-deficient mice subjected to DMM developed worse OA pathologies including exacerbated cartilage damage, osteophyte formation and synovitis relative to C1q-sufficient mice. Our data suggest that C1q deficiency exacerbates inflammation and cartilage damage through mechanisms involving dysregulated macrophage activation. Understanding the precise mechanisms underlying C1q-mediated regulation of inflammation may lead to the identification of novel targets for the treatment of inflammatory diseases including OA.

C1q acts in the tumour microenvironment as a cancer-promoting factor independently of complement activation.

Complement C1q is the activator of the classical pathway. However, it is now recognized that C1q can exert functions unrelated to complement activation. Here we show that C1q, but not C4, is expressed in the stroma and vascular endothelium of several human malignant tumours. Compared with wild-type (WT) or C3- or C5-deficient mice, C1q-deficient (C1qa−/−) mice bearing a syngeneic B16 melanoma exhibit a slower tumour growth and prolonged survival. This effect is not attributable to differences in the tumour-infiltrating immune cells. Tumours developing in WT mice display early deposition of C1q, higher vascular density and an increase in the number of lung metastases compared with C1qa−/− mice. Bone marrow (BM) chimeras between C1qa−/− and WT mice identify non-BM-derived cells as the main local source of C1q that can promote cancer cell adhesion, migration and proliferation. Together these findings support a role for locally synthesized C1q in promoting tumour growth.

AB0175 C1Q Regulates the TLR7-Mediated Inflammatory Response by Pristane-Primed Macrophages: Implications for Pristane-Induced Lupus (PIL)

BackgroundIntraperitoneal injection of the natural oil pristane induces loss of immune tolerance and development of pristane-induced lupus (PIL) in susceptible mouse strains. PIL is characterised by high titres of autoantibodies,...

A Dramatic Increase of C1q Protein in the CNS during Normal Aging

The decline of cognitive function has emerged as one of the greatest health threats of old age. Age-related cognitive decline is caused by an impacted neuronal circuitry, yet the molecular mechanisms responsible are unknown. C1q, the initiating protein of the classical complement cascade and powerful effector of the peripheral immune response, mediates synapse elimination in the developing CNS. Here we show that C1q protein levels dramatically increase in the normal aging mouse and human brain, by as much as 300-fold. This increase was predominantly localized in close proximity to synapses and occurred earliest and most dramatically in certain regions of the brain, including some but not all regions known to be selectively vulnerable in neurodegenerative diseases, i.e., the hippocampus, substantia nigra, and piriform cortex. C1q-deficient mice exhibited enhanced synaptic plasticity in the adult and reorganization of the circuitry in the aging hippocampal dentate gyrus. Moreover, aged C1q-deficient mice exhibited significantly less cognitive and memory decline in certain hippocampus-dependent behavior tests compared with their wild-type littermates. Unlike in the developing CNS, the complement cascade effector C3 was only present at very low levels in the adult and aging brain. In addition, the aging-dependent effect of C1q on the hippocampal circuitry was independent of C3 and unaccompanied by detectable synapse loss, providing evidence for a novel, complement- and synapse elimination-independent role for C1q in CNS aging.

C1q-induced LRP1B and GPR6 Proteins Expressed Early in Alzheimer Disease Mouse Models, Are Essential for the C1q-mediated Protection against Amyloid-β Neurotoxicity

Complement protein C1q is induced in the brain in response to a variety of neuronal injuries, including Alzheimer disease (AD), and blocks fibrillar amyloid-β (fAβ) neurotoxicity in vitro. Here, we show that C1q protects immature and mature primary neurons against fAβ toxicity, and we report for the first time that C1q prevents toxicity induced by oligomeric forms of amyloid-β (Aβ). Gene expression analysis reveals C1q-activated phosphorylated cAMP-response element-binding protein and AP-1, two transcription factors associated with neuronal survival and neurite outgrowth, and increased LRP1B and G protein-coupled receptor 6(GPR6) expression in fAβ-injured neurons. Silencing of cAMP-response element-binding protein, LRP1B or GPR6 expression inhibited C1q-mediated neuroprotection from fAβ-induced injury. In addition, C1q altered the association of oligomeric Aβ and fAβ with neurons. In vivo, increased hippocampal expression of C1q, LRP1B, and GPR6 is observed as early as 2 months of age in the 3 × Tg mouse model of AD, whereas no such induction of LRP1B and GPR6 was seen in C1q-deficient AD mice. In contrast, expression of C1r and C1s, proteases required to activate the classical complement pathway, and C3 showed a significant age-dependent increase only after 10-13 months of age when Aβ plaques start to accumulate in this AD model. Thus, our results identify pathways by which C1q, up-regulated in vivo early in response to injury without the coordinate induction of other complement components, can induce a program of gene expression that promotes neuroprotection and thus may provide protection against Aβ in preclinical stages of AD and other neurodegenerative processes.

Intracerebral immune complex formation induces inflammation in the brain that depends on Fc receptor interaction

In this study, we investigate the underlying mechanisms of antibody-mediated inflammation in the brain. We show that immune complexes formed in the brain parenchyma generate a robust and long-lasting inflammatory response, characterized by increased expression of the microglia markers CD11b, CD68 and FcRII/III, but no neutrophil recruitment. In addition to these histological changes, we observed transient behavioural changes that coincided with the inflammatory response in the brain. The inflammatory and behavioural changes were absent in Fc-gamma chain (Fcγ)-deficient mice, while C1q-deficient mice were not different from wild-type mice. We conclude that, in the presence of antigen, antibodies can lead to a local immune complex-mediated inflammatory reaction in the brain parenchyma and indirectly induce neuronal tissue damage through recruitment and activation of microglia via Fcγ receptors. These observations may have important implications for the development of therapeutic antibodies directed against neuronal antigens used for therapeutic intervention in neurological diseases.

Identification of a Cytochrome P4502E1/Bid/C1q-dependent Axis Mediating Inflammation in Adipose Tissue after Chronic Ethanol Feeding to Mice

Chronic, heavy alcohol exposure results in inflammation in adipose tissue, insulin resistance, and liver injury. Here we have identified a CYP2E1/Bid/C1q-dependent pathway that is activated in response to chronic ethanol and is required for the development of inflammation in adipose tissue. Ethanol feeding for 25 days to wild-type (C57BL/6J) mice increased expression of multiple markers of adipose tissue inflammation relative to pair-fed controls independent of increased body weight or adipocyte size. Ethanol feeding increased the expression of CYP2E1 in adipocytes, but not stromal vascular cells, in adipose tissue and Cyp2e1(-/-) mice were protected from adipose tissue inflammation in response to ethanol. Ethanol feeding also increased the number of TUNEL-positive nuclei in adipose tissue of wild-type mice but not in Cyp2e1(-/-) or Bid (-/-) mice. Apoptosis contributed to adipose inflammation, as the expression of multiple inflammatory markers was decreased in mice lacking the Bid-dependent apoptotic pathway. The complement protein C1q binds to apoptotic cells, facilitating their clearance and activating complement. Making use of C1q-deficient mice, we found that activation of complement via C1q provided the critical link between CYP2E1/Bid-dependent apoptosis and onset of adipose tissue inflammation in response to chronic ethanol. In summary, chronic ethanol increases CYP2E1 activity in adipose, leading to Bid-mediated apoptosis and activation of complement via C1q, finally resulting in adipose tissue inflammation. Taken together, these data identify a novel mechanism for the development of adipose tissue inflammation that likely contributes to the pathophysiological effects of ethanol.

Role of Complement Component C1q in the Onset of Preeclampsia in Mice

Preeclampsia (PE) is a life-threatening, pregnancy-induced disease and a leading cause of maternal and fetal morbidity and mortality. Despite considerable research, the causes of PE remain unclear, and there is no effective treatment. Studies in animal models that resemble this complex pregnancy-related disorder may help to identify possible therapies for PE. Complement component C1q has an important role in trophoblast migration, spiral arteries remodeling, and normal placentation. Here we show that pregnant C1q-deficient (C1q(-/-)) mice recapitulate the key features of human PE: hypertension, albuminuria, endotheliosis, decreased placental vascular endothelial growth factor (VEGF) and elevated levels of soluble VEGF receptor 1 (sFlt-1) that correlate with increased fetal death. In addition, decreased blood flow and increased oxidative stress are observed in placentas from C1q(-/-) mice. Treatment of C1q(-/-) mice with pravastatin restored trophoblast invasiveness, placental blood flow, and angiogenic balance and, thus, prevented the onset of PE. Serum-soluble receptors for VEGF-1 levels were reduced and placental VEGF levels were significantly increased in C1q(-/-) mice treated with pravastatin compared with untreated C1q(-/-) mice (VEGF: 1067±171 versus 419±194 pg/mL; P<0.01). Pravastatin treatment reduced hypertension (change in mean arterial pressure: 1±1 versus 18±3 mm Hg in C1q(-/-) untreated mice), and albuminuria (of creatinine) was reduced from 820±175 to 117±45 μg/mg (both P<0.01). Renal damage and endothelial dysfunction were significantly attenuated with pravastatin. This model that highlights the causative role of impaired trophoblast invasion in the pathogenesis of PE allowed us to identify pravastatin as a good therapeutic option to prevent PE.

The Therapeutic Potential of the Humoral Pattern Recognition Molecule PTX3 in Chronic Lung Infection Caused by Pseudomonas aeruginosa

Chronic lung infections by Pseudomonas aeruginosa strains are a major cause of morbidity and mortality in cystic fibrosis (CF) patients. Although there is no clear evidence for a primary defect in the immune system of CF patients, the host is generally unable to clear P. aeruginosa from the airways. PTX3 is a soluble pattern recognition receptor that plays nonredundant roles in the innate immune response to fungi, bacteria, and viruses. In particular, PTX3 deficiency is associated with increased susceptibility to P. aeruginosa lung infection. To address the potential therapeutic effect of PTX3 in P. aeruginosa lung infection, we established persistent and progressive infections in mice with the RP73 clinical strain RP73 isolated from a CF patient and treated them with recombinant human PTX3. The results indicated that PTX3 has a potential therapeutic effect in P. aeruginosa chronic lung infection by reducing lung colonization, proinflammatory cytokine levels (CXCL1, CXCL2, CCL2, and IL-1β), and leukocyte recruitment in the airways. In models of acute infections and in in vitro assays, the prophagocytic effect of PTX3 was maintained in C1q-deficient mice and was lost in C3- and Fc common γ-chain-deficient mice, suggesting that facilitated recognition and phagocytosis of pathogens through the interplay between complement and FcγRs are involved in the therapeutic effect mediated by PTX3. These data suggested that PTX3 is a potential therapeutic tool in chronic P. aeruginosa lung infections, such as those seen in CF patients.

Complement C1q enhances homing‐related responses of hematopoietic stem/progenitor cells

Previously, we reported that the complement cleavage fragments C3a and C5a are important modulators of trafficking of hematopoietic stem/progenitor cells (HSPCs). The aim of this study was to examine a possible role for complement component 1, subcomponent q (C1q) in HSPC migration. CD34+ HSPCs isolated from cord blood (CB), bone marrow (BM), and granulocyte-colony-stimulating factor (G-CSF)-mobilized peripheral blood (mPB) were evaluated for the expression of C1q and its receptor for phagocytosis (C1qRp) using reverse transcription-polymerase chain reaction, Western blotting, and fluorescence-activated cell sorting. Chemotactic responses and chemoinvasiveness toward stromal cell-derived factor (SDF)-1 and expression of matrix metalloproteinase (MMP)-9 were also examined after C1q stimulation. Moreover, G-CSF- and zymosan-induced mobilization was evaluated in C1q-deficient mice. C1q was expressed in CD34+ cells from mPB, but not from CB or steady-state BM; however, stimulation of the latter with G-CSF induced C1q expression. C1qRp receptor was found on BM, CB, and mPB CD34+ cells and more mature ex vivo expanded myeloid and megakaryocytic precursors. Although C1q itself was not a chemoattractant for HSPCs, it primed/enhanced the chemotactic response of CD34+ cells to a low SDF-1 gradient and their chemoinvasion across the reconstituted basement membrane Matrigel and increased secretion of MMP-9 by these cells. Moreover, in in vivo studies C1q-deficient mice were found to be easy G-CSF mobilizers compared to wild-type mice and normal zymosan mobilizers. We demonstrated that C1q primes the responses of CD34+ HSPCs to an SDF-1 gradient, which may enhance their ability to stay within BM niches, suggesting that the C1q/C1qRp axis contributes to HSPC homing/retention in BM.

Complement and Alcoholic Liver Disease: Role of C1q in the Pathogenesis of Ethanol-Induced Liver Injury in Mice

Complement is involved in the development of alcoholic liver disease in mice; however, the mechanisms for complement activation during ethanol exposure have not been identified. C1q, the recognition subunit of the first complement component, binds to apoptotic cells, thereby activating the classical complement pathway. Because ethanol exposure increases hepatocellular apoptosis, we hypothesized that ethanol-induced apoptosis would lead to activation of complement via the classical pathway. Wild-type and C1qa-/- mice were allowed free access to ethanol-containing diets or pair-fed control diets for 4 or 25 days. Ethanol feeding for 4 days increased apoptosis of Kupffer cells in both wild-type and C1qa-/- mice. Ethanol-induced deposition of C1q and C3b/iC3b/C3c was colocalized with apoptotic Kupffer cells in wild-type, but not C1qa-/-, mice. Furthermore, ethanol-induced increases in tumor necrosis factor-alpha and interleukin-6 expression at this early time point were suppressed in C1q-deficient mice. Chronic ethanol feeding (25 days) increased steatosis, hepatocyte apoptosis, and activity of serum alanine and aspartate aminotransferases in wild-type mice. These markers of hepatocyte injury were attenuated in C1qa-/- mice. In contrast, chronic ethanol (25 days)-induced increases in cytochrome P450 2E1 expression and oxidative stress did not differ between wild-type and C1qa-/- mice. For the first time, these data indicate that ethanol activates the classical complement pathway via C1q binding to apoptotic cells in the liver and that C1q contributes to the pathogenesis of ethanol-induced liver injury.

Synapse Remodeling, Compliments of the Complement System

A growing body of evidence indicates that some proteins known for their immune functions also have distinct nonimmune functions in the normal uninjured central nervous system. In this issue, Stevens et al. (2007) demonstrate an unexpected requirement for molecules of the complement cascade in the remodeling of synaptic connections in the developing visual system.

C1q deficiency promotes the production of transgenic-derived IgM and IgG3 autoantibodies in anti-DNA knock-in transgenic mice

C1q-deficient mice have been shown to develop a lupus-like disease and to display an impaired clearance of apoptotic cells that are enriched in lupus autoantigens. However, the role of C1q in the regulation of autoreactive B cells remains debatable. To explore this we crossed MRL/Mp C1q-deficient mice with knock-in transgenic (Tg) mice expressing an anti-ssDNA antibody (VH3H9R and VH3H9R/VLκ8R). Analysis of the VH3H9R mice showed that in the absence of C1q higher titres of Tg-derived IgM and IgG3 anti-ssDNA antibodies were detectable. In contrast, in the VH3H9R/VLκ8R C1q-deficient animals no increase in Tg antibody levels was observed. In both models the lack of C1q induced a marked reduction of marginal zone B cells and this was paralleled by a significant increase in the percentage of plasmocytes. Thus, one could postulate that in the absence of C1q the failure to clear efficiently dying cells provides an additional stimulus to the autoreactive Tg B cells resulting in their emigration from the marginal zone B cell compartment with subsequent increase in plasmocytes. However, the lack of C1q led to an increased production of Tg IgM and IgG3 antibodies only in VH3H9R mice indicating that additional genetic susceptibility factors are required to break self-tolerance.