Genetic variants in the region of the C1q genes are associated with rheumatoid arthritis

The intricate relationship between autoimmunity disease and neutrophils death patterns: a love-hate story

Autoimmune diseases are pathological conditions that result from the misidentification of self-antigens in immune system, leading to host tissue damage and destruction. These diseases can affect different organs and systems, including the blood, joints, skin, and muscles. Despite the significant progress made in comprehending the underlying pathogenesis, the complete mechanism of autoimmune disease is still not entirely understood. In autoimmune diseases, the innate immunocytes are not functioning properly: they are either abnormally activated or physically disabled. As a vital member of innate immunocyte, neutrophils and their modes of death are influenced by the microenvironment of different autoimmune diseases due to their short lifespan and diverse death modes. Related to neutrophil death pathways, apoptosis is the most frequent cell death form of neutrophil non-lytic morphology, delayed or aberrant apoptosis may contribute to the development anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV). In addition, NETosis, necroptosis and pyroptosis which are parts of lytic morphology exacerbate disease progression through various mechanisms in autoimmune diseases. This review aims to summarize recent advancements in understanding neutrophil death modes in various autoimmune diseases and provide insights into the development of novel therapeutic approaches for autoimmune diseases.

Overview on the Link Between the Complement System and Auto-Immune Articular and Pulmonary Disease

Complement system (CS) dysregulation is a key factor in the pathogenesis of different autoimmune diseases playing a central role in many immune innate and adaptive processes. Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by ta breach of self-tolerance leading to a synovitis and extra-articular manifestations. The CS is activated in RA and seems not only to mediate direct tissue damage but also play a role in the initiation of RA pathogenetic mechanisms through interactions with citrullinated proteins. Interstitial lung disease (ILD) represents the most common extra-articular manifestation that can lead to progressive fibrosis. In this review, we focused on the evidence of CS dysregulation in RA and in ILD, and highlighted the role of the CS in both the innate and adaptive immune responses in the development of diseases, by using idiopathic pulmonary fibrosis as a model of lung disease. As a proof of concept, we dissected the evidence that several treatments used to treat RA and ILD such as glucocorticoids, pirfenidone, disease modifying antirheumatic drugs, targeted biologics such as tumor necrosis factor (TNF)-inhibitors, rituximab, tocilizumab, and nintedanib may act indirectly on the CS, suggesting that the CS might represent a potential therapeutic target in these complex diseases.

The complement system and human autoimmune diseases

Genetic deficiencies of early components of the classical complement activation pathway (especially C1q, r, s, and C4) are the strongest monogenic causal factors for the prototypic autoimmune disease systemic lupus erythematosus (SLE), but their prevalence is extremely rare. In contrast, isotype genetic deficiency of C4A and acquired deficiency of C1q by autoantibodies are frequent among patients with SLE. Here we review the genetic basis of complement deficiencies in autoimmune disease, discuss the complex genetic diversity seen in complement C4 and its association with autoimmune disease, provide guidance as to when clinicians should suspect and test for complement deficiencies, and outline the current understanding of the mechanisms relating complement deficiencies to autoimmunity. We focus primarily on SLE, as the role of complement in SLE is well-established, but will also discuss other informative diseases such as inflammatory arthritis and myositis.

The differences in serum C1q levels between first-episode patients with bipolar disorder and major depressive disorder

OBJECTIVE

This study aimed at exploring the changes of serum complement C1q levels in patients with Bipolar Disorder (BD) using a cross-sectional design, and the differences between Major Depressive Disorder (MDD) and BD. Moreover, the correlation between complement C1q and bech-rafaelsdn mania rating scales (BRMS) in patients with MDD and BD was assessed.

METHODS

Serum complement C1q levels were measured by ADVIA 2400 biochemical analyser in 104 patients with MDD, 71 patients with BD type I and 42 patients with BD type II diagnosed by Diagnostic and Statistical of Mental Disorder 5 (DSM-5). Then simple and multivariate linear regression analysis was conducted between the level of serum C1q and BRMS among patients with BD.

RESULTS

The serum complement C1q levels were higher in BD type I than BD type II (P < 0.001); Serum complement C1q levels were higher in MDD than BD type II (P < 0.001). We discovered that there was a positive correlation relationship between serum complement C1q levels and BRMS in BD type I (r = 0.756, P < 0.001).

CONCLUSION

We confirmed that serum complement C1q levels were higher in patients with BD type II than in MDD patients. These current results support the view that the complement C1q may play an important role in the pathophysiology of BD. Serum complement C1q was strongly associated with BD and is worth investigating in future studies.

Complement System Inhibition Modulates the Inflammation Induced by the Venom of Premolis semirufa, an Amazon Rainforest Moth Caterpillar

The caterpillar of the Premolis semirufa moth, commonly called Pararama, is found in the Brazilian Amazon region. Contact with the hairs can cause a chronic inflammatory reaction, termed "pararamosis". To date, there is still no specific treatment for pararamosis. In this study, we used a whole human blood model to evaluate the involvement of the complement in the proinflammatory effects of P. semirufa hair extract, as well as the anti-inflammatory potential of complement inhibitors in this process. After treatment of blood samples with the P. semirufa hair extract, there was a significant increase in the generation of soluble terminal complement complex (sTCC) and anaphylatoxins (C3a, C4a, and C5a), as well as the production of the cytokines TNF-α and IL-17 and the chemokines IL-8, RANTES, MIG, MCP-1, and IP-10. The inhibition of C3 with compstatin significantly decreased IL-17, IL-8, RANTES, and MCP-1 production. However, the use of the C5aR1 antagonist PMX205 promoted a reduction in the production of IL-8 and RANTES. Moreover, compstatin decreased CD11b, C5aR1, and TLR2 expression induced by P. semirufa hair extract in granulocytes and CD11b, TLR4, and TLR2 in monocytes. When we incubated vascular endothelial cells with extract-treated human plasma, there was an increase in IL-8 and MCP-1 production, and compstatin was able to decrease the production of these chemokines. C5aR1 antagonism also decreased the production of MCP-1 in endothelial cells. Thus, these results indicate that the extract of the Pararama bristles activates the complement system and that this action contributes to the production of cytokines and chemokines, modulation of the expression of surface markers in leukocytes, and activation of endothelial cells.

The C1q-ApoE complex: A new hallmark pathology of viral hepatitis and nonalcoholic fatty liver disease

We recently identified a high-affinity C1q-ApoE complex in human artery atherosclerotic intima lesions and in human amyloid plaques of Alzheimer's Disease brains defining a common pathogenetic pathway of two diverse diseases, i.e. atherosclerosis and dementia. C1q is the initiating and controlling protein of the classical complement cascade (CCC), which occupies a key role in multiple acute and chronic inflammatory tissue responses. C1q is largely produced by myeloid cells including Kupffer cells (KCs) and subsequently secreted into the circulation as an inactive preprotein. Its binding partner, Apolipoprotein E (ApoE), is produced by KCs and hepatocytes and it is also secreted into the circulation, where it regulates essential steps of lipid transport. In addition to its major source, ApoE can be produced by non-liver cells including immune cells and multiple other cells depending on local tissue contexts. To initiate the CCC cascade, C1q must be activated by molecules as varied as oxidized lipids, amyloid fibrils, and immune complexes. However, ApoE is mute towards inactive C1q but binds at high-affinity to its activated form. Specifically, our studies revealed that ApoE is a CCC-specific checkpoint inhibitor via the formation of the C1q-ApoE complex. We proposed that it may arise in multiple if not all CCC-associated diseases and that its presence indicates ongoing CCC activity. Here, we turned to the liver to examine C1q-ApoE complexes in human B- and C-viral hepatitis and nonalcoholic fatty liver disease (NAFLD). In addition, we used multidrug-resistance-2 gene-knockout (Mdr2-KO) mice as a model for inflammatory liver disease and hepatocellular carcinoma (HCC) pathogenesis. In normal murine and human livers, KCs were the major C1q-producing cell type while hepatocytes were the primary ApoE-forming cell type though the C1q-ApoE complex was rare or nonexistent. However, significant numbers of C1q-ApoE complexes formed in both Mdr2-KO, human viral hepatitis, and NAFLD around portal triads where immune cells had infiltrated the liver. Additionally, high numbers of C1q-ApoE complexes emerged in human livers in areas of extracellular lipid droplets across the entire liver parenchyma in NAFLD-affected patients. Thus, the C1q-ApoE complex is a new pathological hallmark of viral hepatitis B and C and NAFLD.

Association of C1q gene cluster variants with rheumatoid arthritis: a pilot study

Single-nucleotide polymorphisms (SNPs) in C1q gene cluster were previously linked to autoimmunity and SLE, but data are scarce for their association with RA. In the present study, we evaluated associations of five SNPs (rs665691, rs682658, rs172378, rs292001 and rs294179) in the C1q genetic region with RA and some of its clinical and immunologic characteristics. Fifty-eight RA patients and 67 age- and gender-matched healthy controls, all Caucasian, participated in the study. They were genotyped for the five SNPs using TaqMan allelic discrimination assay, and their C1q levels were estimated by ELISA. Rheumatoid factor and anti-citrullinated peptide antibodies were measured (using latex agglutination and ELISA resp.) in the RA patients' group and relevant clinical information was collected. RA patients and healthy controls had similar frequencies of alleles and genotypes of rs665691, rs682658 and rs294179. Minor G-allele and GG genotype of rs172378 were associated with RA (OR = 2.80; 95% CI 1.62-4.81; p = 0.0002 and OR = 5.01; 95% CI 1.55-16.24; p = 0.007, resp.), as well as AA genotype of rs292001 (OR = 3.23; 95% CI 1.15-9.08; p = 0.026). C1q levels were significantly lower (still normal) in RA patients' group compared to healthy volunteers: 89 µg/ml (68-121) vs 114 µg/ml (60-169), p < 0.0001. Significant association was established between rs172378 and rs292001 and RA, in contrast to rs665691, rs682658 and rs294179. RA patients had lower C1q levels than healthy controls. Our findings correspond to the scientific knowledge so far and add additional clarity from a Bulgarian cohort.

Circulating C1q levels in health and disease, more than just a biomarker

C1q is the recognition molecule of the classical pathway of the complement system. By binding to its targets, such as antigen-bound immunoglobulins or C-reactive protein, C1q contributes to the innate defense against infections. However, C1q also plays several other roles beyond its traditional role in complement activation. Circulating levels of C1q are determined in routine diagnostics as biomarker in several diseases. Decreased C1q levels are present in several autoimmune conditions. The decreased levels reflect the consumption of C1q by complement activation and serves as a biomarker for disease activity. In contrast, increased C1q levels are present in infectious and inflammatory diseases and may serve as a diagnostic biomarker. The increased levels of C1q are still incompletely understood but are suggested to modulate the adaptive immune response as C1q is known to impact on the maturation status of antigen-presenting cells and C1q impacts directly on T cells leading to decreased T-cell activity in high C1q conditions. In this review, we provide a comprehensive overview of the current literature on circulating levels of C1q in health and disease, and discuss how C1q can both protect against infections as well as maintain tolerance by regulating adaptive immunity.

Identification of Novel Targets of Knee Osteoarthritis Shared by Cartilage and Synovial Tissue

Arthritis is the leading cause of disability among adults, while osteoarthritis (OA) is the most common form of arthritis that results in cartilage loss. However, accumulating evidence suggests that the protective hyaline cartilage should not be the sole focus of OA treatment. Particularly, synovium also plays essential roles in OA’s initiation and progression and warrants serious consideration when battling against OA. Thus, biomarkers with similar OA-responsive expressions in cartilage and synovium should be the potential targets for OA treatment. On the other hand, molecules with a distinguished response during OA in cartilage and synovium should be ruled out as OA therapeutic(s) to avoid controversial effects in different tissues. Here, to pave the path for developing a new generation of OA therapeutics, two published transcriptome datasets of knee articular cartilage and synovium were analyzed in-depth. Genes with statistically significantly different expression in OA and healthy cartilage were compared with those in the synovium. Thirty-five genes with similar OA-responsive expression in both tissues were identified while recognizing three genes with opposite OA-responsive alteration trends in cartilage and synovium. These genes were clustered based on the currently available knowledge, and the potential impacts of these clusters in OA were explored.

Establishment of anti-C1q monoclonal antibodies to measure serum C1q levels discriminating disease severity subsets of rheumatoid arthritis within 5 years of onset

Objectives: To establish anti-C1q monoclonal antibodies which can measure serum C1q levels discriminating disease severity subsets of rheumatoid arthritis (RA) within 5 years of onset.Methods: In this multi-centre, longitudinal, observational study, 122 RA patients [102 females, baseline age 58.5 years, rheumatoid factor (RF) positivity 78.7%, serum C-reactive protein (CRP) 1.2 mg/dl, and concomitant methotrexate (MTX) 4.9 mg/week (29.5%)] within 5 years of onset (disease duration 21.0 months) were enrolled from 1985 to 2000. Patients were not treated by more than 8 mg/week of MTX or biologics which may strongly affect the course of joint destruction. Disease severity at 10-15 years of onset was classified according to the number of destructed joints of overall 68 joints on plain radiographs (36 patients were mild RA group involving only peripheral joints and 86 were severe RA group involving large axial joints). Baseline serum C1q levels were evaluated by ELISA with newly developed 4 monoclonal anti-C1q antibodies, and compared between two groups as well as conventional RA disease activity markers.Results: There were no significant differences between two groups in baseline conventional RA disease activity markers such as RF, erythrocyte sedimentation rate, CRP, and matrix metalloproteinase-3. However, compared to mild RA group, severe RA group showed higher baseline serum C1q levels (μg/ml) evaluated by anti-C1q monoclonal antibodies of no.33 (104.8 ± 22.3 vs. 118.3 ± 19.3; p = .0024), no. 40 (102.6 ± 21.9 vs 121.2 ± 22.3; p = .000069), no. 54 (102.1 ± 22.5 vs. 119.3 ± 26.9; p = .00052), and no. 76 (105.6 ± 21.8 vs. 122.6 ± 26.4; p = .00043). Receiver operating characteristic curve analysis revealed that in patients with serum C1q levels of ≥110.5 μg/ml (measured by antibody no. 40), 78.9% (75/95) belonged to severe RA group.Conclusion: Measuring serum C1q levels of RA within 5 years of onset by newly developed anti-C1q antibodies may be useful in predicting the prognosis of disease severity evaluated by the extent of joint destruction.

Cq1 Exon Polymorphisms in Caucasian and African American Systemic Lupus Erythematosus patients

BACKGROUND

C1q protein is composed of three protein chains (A, B and C) that are the products of separate genes. Genetic deficiencies in C1Q genes are important factors influencing the risk of systemic lupus erythematosus (SLE). Therefore, this study aimed to investigate the possible association of single nucleotide polymorphisms (SNPs) in the coding region of the C1Q genes with SLE.

METHODS

To search for potential SNPs in the encoding regions of C1q A, B and C chains, Cq1 exons were initially amplified and directly sequenced from leukocyte DNA from a subset of Caucasian and African American SLE patients and healthy controls. The sequences were analyzed by the Phrap and Phred software analysis system and the SNPs were identified by visual inspection. To test if any of these SNPs were linked to susceptibility to SLE, they were measured in 210 SLE patients ((59 African Americans and 151 Caucasians) and 129 matched healthy controls (55 African Americans and 74 Caucasians) by restriction fragment length polymorphism analysis.

RESULTS

The sequencing phase of the study identified three synonymous SNPs: Nucleotide 276G>A in C1QA, 66C>A in C1QB and 129G>A in C1QC. Statistically, no differences were found in genotype or allele frequencies between patients and controls for the 276G>A or 66C>A SNP. However, in Caucasians, the frequencies of the 129G>A genotypes were significantly different between SLE patients and controls (P = 0.005), specifically with the GG genotype being over represented in the controls (P = 0.004).

CONCLUSION

The results show that the homozygous 129GG genotype is associated with protection against SLE onset. This protection is race dependent, being observed in Caucasians but not African Americans. The mechanism of this association is currently unclear.

Complement and its environmental determinants in the progression of human rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex autoimmune disease with an etiology that is not yet well understood, disproportionally affects women and also varies in incidence and prevalence by population. The presence of anti-citrullinated protein antibodies (ACPA) is a highly specific biomarker for the diagnosis of clinically apparent RA. ACPA are also present in the serum for an average of 3-5 years prior to the onset of RA during an asymptomatic period characterized by mucosal inflammation and local ACPA production at these sites. We hypothesized that systemic complement activation products might be generated during the pre-clinical initiation of RA and/or provide a second hit that promotes subsequent arthritis development in the joints. In addition, we evaluated which demographic and genetic features and environmental exposures could influence the complement activation process. We analyzed plasma from healthy subjects, subjects at-risk for the development of RA based on serum ACPA positivity in absence of inflammatory arthritis (IA), and ACPA positive RA subjects by Multiplex Assay and ELISA for eighteen complement system components, factors and activation products belonging to the classical, lectin and alternative pathways. By using regression models, associations between complement proteins and various demographic, genetic, and environmental factors previously found to be associated with RA, including sex, smoking, shared epitope, and oral contraceptive use, were examined. We found no evidence of systemic complement activation in ACPA positive subjects without IA, but in contrast found evidence of systemic involvement of the both classical and alternative pathways during the stage of the disease where classified RA is present, (i.e. during joint inflammation and damage). With regard to the demographic, genetic, and environmental variables, females who reported current or past oral contraceptive use and subjects with current tobacco exposure demonstrated alterations of the alternative pathway of complement. Furthermore, RA subjects with established disease who have a body mass index categorized as obese demonstrated higher levels of C2 compared to RA subjects who are not considered obese. In sum, the complement system may be involved in the pathogenesis of RA, with only localized mucosal effects during the preclinical period in those at-risk for RA but in the joint as well as systemically in those who have developed clinically apparent arthritis.

Epidemiology of ATTRV30M neuropathy in Cyprus and the modifier effect of complement C1q on the age of disease onset

BACKGROUND

ATTRV30M amyloidosis is a lethal autosomal dominant sensorimotor and autonomic neuropathy caused by amyloid deposition composed of aggregated misfolded TTR monomers with the V30M mutation. The age of onset in patients with ATTRV30M varies in different foci and the mechanism behind it is still unknown.

METHODS

The tertiary neurology center following all ATTRV30M patients in Cyprus was used to collect demographic data to estimate; prevalence, incidence, penetrance, anticipation, time from disease onset to diagnosis and transplantation. Ocular, cardiac and leptomeningeal involvement in transplanted patients was explored. Correlation of C1q tagging SNPs with age of disease onset was carried out.

RESULTS

Prevalence and incidence for ATTRV30M neuropathy in Cyprus are 5.4/100,000 and 0.3/100,000 respectively. Mean age of onset is 40.6 years and anticipation is 8.3 years. Penetrance reaches 51% and 75% by the ages of 50 and 80 years respectively. In liver transplanted patients rates of ocular, cardiac and leptomeningeal involvement were estimated to be 60%, 20% and 16%, respectively. C1q polymorphisms correlated with age of disease onset.

CONCLUSIONS

ATTRV30M neuropathy has a rising prevalence in Cyprus due to improved survival of patients. Late onset complications are becoming a major problem. Complement C1q appears to be a modifier in this disease.

Common and rare genetic variants of complement components in human disease

Genetic variability in the complement system and its association with disease has been known for more than 50 years, but only during the last decade have we begun to understand how this complement genetic variability contributes to the development of diseases. A number of reports have described important genotype-phenotype correlations that associate particular diseases with genetic variants altering specific aspects of the activation and regulation of the complement system. The detailed functional characterization of some of these genetic variants provided key insights into the pathogenic mechanisms underlying these pathologies, which is facilitating the design of specific anti-complement therapies. Importantly, these analyses have sometimes revealed unknown features of the complement proteins. As a whole, these advances have delineated the functional implications of genetic variability in the complement system, which supports the implementation of a precision medicine approach based on the complement genetic makeup of the patients. Here we provide an overview of rare complement variants and common polymorphisms associated with disease and discuss what we have learned from them.

Proteinase 3 Interferes With C1q-Mediated Clearance of Apoptotic Cells

Proteinase 3 (PR3) is the autoantigen in granulomatosis with polyangiitis, an autoimmune necrotizing vasculitis associated with anti-neutrophil cytoplasmic antibodies (ANCAs). Moreover, PR3 is a serine protease whose membrane expression can potentiate inflammatory diseases such as ANCA-associated vasculitis and rheumatoid arthritis. During apoptosis, PR3 is co-externalized with phosphatidylserine (PS) and is known to modulate the clearance of apoptotic cells through a calreticulin (CRT)-dependent mechanism. The complement protein C1q is one mediator of efferocytosis, the clearance of altered self-cells, particularly apoptotic cells. Since PR3 and C1q are both involved in the clearance of apoptotic cells and immune response modulation and share certain common ligands (i.e., CRT and PS), we examined their possible interaction. We demonstrated that C1q binding was increased on apoptotic rat basophilic leukemia (RBL) cells that expressed PR3, and we demonstrated the direct interaction between purified C1q and PR3 molecules as shown by surface plasmon resonance. To better understand the functional consequence of this partnership, we tested C1q-dependent phagocytosis of the RBL cell line expressing PR3 and showed that PR3 impaired C1q enhancement of apoptotic cell uptake. These findings shed new light on the respective roles of C1q and PR3 in the elimination of apoptotic cells and suggest a novel potential axis to explore in autoimmune diseases characterized by a defect in apoptotic cell clearance and in the resolution of inflammation.

Complement C1q expression in Erythema nodosum leprosum

Complement C1q is a soluble protein capable of initiating components of the classical pathway in host defence system. In earlier qualitative studies, C1q has been implicated in the pathogenesis of Erythema Nodosum Leprosum (ENL). However, little is known about the role of this complement in ENL reaction. In the present study we described the protein level of C1q production and its gene expression in the peripheral blood and skin biopsies in patients with ENL reaction and lepromatous leprosy (LL) patient controls before and after treatment. Thirty untreated patients with ENL reaction and 30 non-reactional LL patient controls were recruited at ALERT Hospital, Ethiopia. Peripheral blood and skin biopsies were obtained from each patient before and after treatment. The level of circulating C1q in the plasma was determined by enzyme-linked immunosorbent assay. The mRNA expression of the three C1q components, C1qA, C1qB, and C1qC in the peripheral blood and skin biopsies was determined by qPCR. Circulating C1q in the peripheral blood of untreated ENL patients was significantly decreased compared to LL patient controls. Untreated ENL patients had increased C1q gene expression in the peripheral blood compared to LL controls. Similarly, C1qA and C1qC gene expression were substantially increased in the skin biopsies of untreated ENL patients compared to LL controls. However, after treatment none of these genes show significant difference in both groups. In conclusion, while circulating C1q is inversely correlated with active ENL reactions, its gene expression is directly correlated with ENL. The decreased circulating C1q may suggest the utilization of C1q in immune-complex formation in these patients. Therefore, C1q could be a potential diagnostic marker for active ENL reactions as well as for monitoring ENL treatment.

Is the A-Chain the Engine That Drives the Diversity of C1q Functions? Revisiting Its Unique Structure

The immunopathological functions associated with human C1q are still growing in terms of novelty, diversity, and pathologic relevance. It is, therefore, not surprising that C1q is being recognized as an important molecular bridge between innate and adaptive immunity. The secret of this functional diversity, in turn, resides in the elegant but complex structure of the C1q molecule, which is assembled from three distinct gene products: A, B, and C, each of which has evolved from a separate and unique ancestral gene template. The C1q molecule is made up of 6A, 6B, and 6C polypeptide chains, which are held together through strong covalent and non-covalent bonds to form the 18-chain, bouquet-of-flower-like protein that we know today. The assembled C1q protein displays at least two distinct structural and functional regions: the collagen-like region (cC1q) and the globular head region (gC1q), each being capable of driving a diverse range of ligand- or receptor-mediated biological functions. What is most intriguing, however, is the observation that most of the functions appear to be predominantly driven by the A-chain of the molecule, which begs the question: what are the evolutionary modifications or rearrangements that singularly shaped the primordial A-chain gene to become a pluripotent and versatile component of the intact C1q molecule? Here, we revisit and discuss some of the known unique structural and functional features of the A-chain, which may have contributed to its versatility.

Association between C1q gene polymorphisms and autoimmune thyroid diseases

OBJECTIVE

In the present study, we aimed to assess the associations of C1q gene polymorphisms with autoimmune thyroid diseases (AITD) susceptibility.

SUBJECTS AND METHODS

A set of 1,003 AITD patients (661 with Graves' disease and 342 with Hashimoto's thyroiditis) and 880 ethnically- and geographically-matched controls from Chinese Han population were included. Five common single nucleotide polymorphisms (SNPs) (rs294185, rs292001, rs682658, rs665691 and rs294179) in C1q gene locus were genotyped. Frequencies of genotypes and alleles were compared between patients and controls, and haplotype analysis was also performed.

RESULTS

There was no statistically significant difference between AITD patients and controls in the frequencies of alleles of rs294185 (P = 0.41), rs292001 (P = 0.71), rs682658 (P = 0.68), rs665691 (P = 0.68) and rs294179 (P = 0.69). There was also no statistically significant difference between AITD patients and controls in the frequencies of genotypes of rs294185 (P = 0.72), rs292001 (P = 0.89), rs682658 (P = 0.83), rs665691 (P = 0.90) and rs294179 (P = 0.43). Stratified analyses showed that none of those five SNPs in C1q gene were associated with Graves' disease or Hashimoto's thyroiditis (all P values > 0.05). Haplotype analysis revealed that there were no obvious genetic associations of C1q gene polymorphisms with AITD susceptibility.

CONCLUSIONS

We, for the first time, identified the associations between C1q gene SNPs and AITD, and our findings suggested that five common SNPs in C1q gene were not associated with AITD susceptibility in Chinese Han population.

Arthritis models: usefulness and interpretation

Animal models of arthritis are used to better understand pathophysiology of a disease or to seek potential therapeutic targets or strategies. Focusing on models currently used for studying rheumatoid arthritis, we show here in which extent models were invaluable to enlighten different mechanisms such as the role of innate immunity, T and B cells, vessels, or microbiota. Moreover, models were the starting point of in vivo application of cytokine-blocking strategies such as anti-TNF or anti-IL-6 treatments. The most popular models are the different types of collagen-induced arthritis and arthritis in KBN mice. As spontaneous arthritides, human TNF-α transgenic mice are a reliable model. It is mandatory to use animal models in the respect of ethical procedure, particularly regarding the number of animals and the control of pain. Moreover, design of experiments should be of the highest level, animal models of arthritis being dedicated to exploration of well-based novelties, and never used for confirmation or replication of already proven concepts. The best interpretations of data in animal models of arthritis suppose integrated research, including translational studies from animals to humans.

C1q as an autocrine and paracrine regulator of cellular functions

Most of the complement proteins in circulation are, by and large, synthesized in the liver. However data accumulated over the past several decades provide incontrovertible evidence that some if not most of the individual complement proteins are also synthesized extrahepatically by activated as well as non-activated cells. The question that is finally being addressed by various investigators is: are the locally synthesized proteins solely responsible for the myriad of biological functions in situ without the contribution of systemic complement? The answer is probably "yes". Among the proteins that are synthesized locally, C1q takes center stage for several reasons. First, it is synthesized predominantly by potent antigen presenting cells such as monocytes, macrophages and dendritic cells (DCs), which by itself is a clue that it plays an important role in antigen presentation and/or DC maturation. Second, it is transiently anchored on the cell surface via a transmembrane domain located in its A chain before it is cleaved off and released into the pericellular milieu. The membrane-associated C1q in turn, is able to sense danger patterns via its versatile antigen-capturing globular head domains. More importantly, locally synthesized C1q has been shown to induce a plethora of biological functions through the induction of immunomodulatory molecules by an autocrine- or paracrine- mediated signaling in a manner that mimics those of TNFα. These include recognition of pathogen- and danger- associated molecular patterns, phagocytosis, angiogenesis, apoptosis and induction of cytokines or chemokines that are important in modulating the inflammatory response. The functional convergence between C1q and TNFα in turn is attributed to their shared genetic ancestry. In this paper, we will infer to the aforementioned "local-synthesis-for-local function" paradigm using as an example, the role played by locally synthesized C1q in autoimmunity in general and in systemic lupus erythematosus in particular.

SLE-associated risk factors affect DC function

Numerous risk alleles for systemic lupus erythematosus (SLE) have now been identified. Analysis of the expression of genes with risk alleles in cells of hematopoietic origin demonstrates them to be most abundantly expressed in B cells and dendritic cells (DCs), suggesting that these cell types may be the drivers of the inflammatory changes seen in SLE. DCs are of particular interest as they act to connect the innate and the adaptive immune response. Thus, DCs can transform inflammation into autoimmunity, and autoantibodies are the hallmark of SLE. In this review, we focus on mechanisms of tolerance that maintain DCs in a non‐activated, non‐immunogenic state. We demonstrate, using examples from our own studies, how alterations in DC function stemming from either DC‐intrinsic abnormalities or DC‐extrinsic regulators of function can predispose to autoimmunity.

Fundamental role of C1q in autoimmunity and inflammation

C1q, historically viewed as the initiating component of the classical complement pathway, also exhibits a variety of complement-independent activities in both innate and acquired immunity. Recent studies focusing on C1q's suppressive role in the immune system have provided new insight into how abnormal C1q expression and bioactivity may contribute to autoimmunity. In particular, molecular networks involving C1q interactions with cell surface receptors and other ligands are emerging as mechanisms involved in C1q's modulation of immunity. Here, we discuss the role of C1q in controlling immune cell function, including recently elucidated mechanisms of action, and suggest how these processes are critical for maintaining tissue homeostasis under steady-state conditions and in preventing autoimmunity.

Fc-Gamma Receptor Polymorphisms Predispose Patients to Infectious Complications After Liver Transplantation

We investigated the impact of polymorphisms in host innate immunoregulatory genes on the development of infectious complications after liver transplantation (LT). The single-nucleotide polymorphisms (SNPs) of C1QA [276A/G], FCGR2A [131H/R], and FCGR3A [158F/V], genes encoding the Fc gamma receptor (FcγR), were analyzed in 89 living donor LT recipients in relation to the occurrences of postoperative infectious complications within 30 days after LT. Consistent with a lower affinity of the isoform encoded by FCGR3A [158F] to both IgG1 and IgG3, a significantly higher incidence of bloodstream infections (BSI) was observed in the FCGR3A [158F/V or F/F] than in the FCGR3A [158V/V] individuals. The combination of FCGR2A and FCGR3A SNPs further stratified the incidence of BSI, regardless of C1QA SNP. The predominant causative pathogen of BSI in the FCGR3A [158F/F or F/V] patients was gram-positive cocci (73.3%), of which one third was methicillin-resistant Staphylococcus aureus. No differences were observed in the incidence of fungal infections or in cytomegalovirus infections with respect to the three gene polymorphisms. Our findings indicate that FcγR SNPs are predisposing factors for BSI and can predict mortality after LT. This study provides a foundation for further prospective studies on a larger scale.

Fingerprinting of anti-citrullinated protein antibodies (ACPA): specificity, isotypes and subclasses

Anti-citrullinated protein antibodies (ACPA) are a family of rheumatoid arthritis (RA)-specific autoantibodies that recognize the amino acid citrulline, resulting from the post-translational modification of arginine. Peptidyl arginine deiminase, the enzyme responsible for citrullination, is present in humans in different isoforms with different tissue distribution, enzymatic activity and target specificity; nonetheless, the number of proteins citrullinated in physiological or pathological conditions is wide, but not every citrullinated protein is a target for antibodies. In pre-RA patients the immune response to citrullinated antigens is initially restricted, expands with time and, after the onset of the disease, is relatively stable. ACPA are heterogeneous in terms of not only fine specificity but also isotype and IgG subclasses usage. This heterogeneity may be relevant for the immunopathogenesis of RA, conditioning the interaction of antibodies with complement and Fc receptors.

Autoimmunity in 2013

The peer-reviewed publications in the field of autoimmunity published in 2013 represented a significant proportion of immunology articles and grew since the previous year to indicate that more immune-mediated phenomena may recognize an autoimmune mechanism and illustrated by osteoarthritis and atherosclerosis. As a result, our understanding of the mechanisms of autoimmunity is becoming the paradigm for translational research in which the progress in disease pathogenesis for both tolerance breakdown and inflammation perpetuation is rapidly followed by new treatment approaches and clinical management changes. The similarities across the autoimmune disease spectrum outnumber differences, particularly when treatments are compared. Indeed, the therapeutics of autoimmune diseases are based on a growing armamentarium that currently includes monoclonal antibodies and small molecules which act by targeting molecular markers or intracellular mediators with high specificity. Among the over 100 conditions considered as autoimmune, the common grounds are well illustrated by the data reported for systemic lupus erythematosus and rheumatoid arthritis or by the plethora of studies on Th17 cells and biomarkers, particularly serum autoantibodies. Further, we are particularly intrigued by studies on the genomics, epigenetics, and microRNA at different stages of disease development or on the safe and effective use of abatacept acting on the costimulation of T and B cells in rheumatoid arthritis. We are convinced that the data published in 2013 represent a promising background for future developments that will exponentially impact the work of laboratory and clinical scientists over the next years.

C1q rs292001 polymorphism and C1q antibodies in juvenile lupus and their relation to lupus nephritis

C1q deficiency is related strongly to systemic lupus erythematosus (SLE), but very few and inconsistent studies explored the single nucleotide polymorphisms of the C1q gene in relation to juvenile SLE (jSLE) and lupus nephritis (LN). The objective of this study was to analyse whether C1q rs 292001 polymorphism is associated with SLE and disease phenotype, especially nephritis, and to investigate the relation between this polymorphism and clinical data, treatment outcome, serum level of C1q protein and antibodies. Typing of C1q rs292001 polymorphism using restriction fragment length polymorphism and measuring serum levels of C1q protein and antibodies by enzyme-linked immunosorbent assay (ELISA) were performed for 130 children with SLE and 208 healthy controls. The A allele of C1q rs292001 was associated with jSLE and LN (P = 0·005 and 0·013, respectively) and the AA genotype was associated with jSLE (P = 0·036). Low serum levels of C1q protein were found in jSLE and LN (P < 0·001 and 0·009, respectively), and these levels were increased after treatment in patients with LN (P = 0·009) and active renal disease (P = 0·027). Higher titres of C1q antibodies were found in patients with LN (P = 0·015) and correlated negatively with C1q protein level (P < 0·001) and patient age (P = 0·04). The A allele and AA genotype of C1q rs292001 can be considered a susceptibility risk factor and the GG genotype could be considered protective for jSLE and LN in the studied cohort of Egyptian children. Decreased serum levels of C1q protein and increased titres of C1q antibodies may be involved in the pathogenesis of jSLE, especially LN.

Classical pathway deficiencies - A short analytical review

Deficiencies in the classical pathway of complement activation have some common features but show also great differences. Deficiencies of each of the components (C1q, C1s, C1r, C4 and C2) imply increased susceptibility to bacterial infections. They are also associated with increased risk to develop systemic lupus erythematosus where deficiency of C1q is strongly associated to the disease while C4 less and C2 much less. Deficiency of C1q affects only activation of the classical pathway while deficiency of C4 and C2 also prevent activation of the lectin pathway. Bypass mechanisms may result in complement activation also in absence of C2 but not in absence of C1q or C4. The genes for C2 and C4 isotypes are closely located within the MHC class III region on chromosome 6p and the genes for the 3 C1q chains are on chromosome 1p. Deficiencies of C1q and of C4 show genetic heterogeneity while deficiency of C2 in the great majority of cases is caused by a specific deletion. The production of C4 and C2 is mainly by the hepatocytes in the liver while C1q is produced by monocytic bone marrow derived cells. This has implications for the possibility to treat the deficiency and hematopoietic stem cell transplantation has been tried in C1q deficiency.

C1q, antibodies and anti-C1q autoantibodies

The complement system has long been known for its role in combating infections. More recently the complement system is becoming increasingly appreciated for its role in processes that range from waste transport, immune tolerance and shaping of the adaptive immune response. Antibodies represent the humoral part of the adaptive immune response and the complement system interacts with antibodies in several ways. Activated complement fragments impact on the production of antibodies, the complement system gets activated by antibodies and complement proteins can be the target of (auto)antibodies. In this review, written to celebrate the contributions of Prof. Dr. M.R. Daha to the field of immunology and especially complement, we will focus on C1q and its various interactions with antibodies. We will specifically focus on the mechanisms by which C1q will interact with monomeric IgG versus polymerized IgG and fluid-phase IgM versus solid-phase IgM. In addition in this review we will discuss in detail how C1q itself is targeted by autoantibodies and how these autoantibodies are currently considered to play a role in human disease.

Investigation of Transcriptional Gene Profiling in Normal Murine Hair Follicular Substructures Using Next-Generation Sequencing to Provide Potential Insights Into Skin Disease

Skin diseases, including hair-related diseases and neoplasia, are a major public health problem. While their prevalence is increasing, their treatment options are limited. Researchers have tried to investigate the genes and signal pathways underlying hair follicles (HFs) to develop genetically targeted therapies through microarrays, which represent an appropriate modality for the analysis of small genomes. To enable the comprehensive transcriptome analysis of large and/or complex transcriptomes, we performed RNA-seq using next-generation sequencing (NGS). We isolated interfollicular keratinocytes (IFKs), HFs, and dermal fibroblasts including dermal papilla cells (DFs-DPCs) from normal C57BL/6 murine skin, transplanted combinations of these samples into nude mice, and followed the mice over time. Sustained hair growth was supported by HFs and DFs-DPCs. We then investigated the pathways and the relevant gene ontology associated with any identified differentially expressed genes (DEGs). In addition, in the culture and flow cytometry (FCM), the HFs had a more quiescent cell cycle pattern than did the IFKs and DFs-DPCs. Therefore, the representative cell cycle-related gene expression of IFKs, HFs, and DFs-DPCs was analyzed by NGS. Our study will allow researchers to further investigate the potential interactions and signaling pathways that are active in HF-related diseases and cancer and may aid in future bioengineering applications.

Variation in complement protein C1q is not a major contributor to cognitive impairment in Parkinson's disease

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Cognitive decline is a strong hallmark of PD.

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Genetic variation in C1Q – does not account for the cognitive decline seen in PD.

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Genetic variation in C1Q – is unlikely to contribute to PD aetiology.

Traditional dogma regarding the brain as an immune exempt organ has changed in recent years. New research has highlighted the role of the classical complement cascade in both synaptic elimination and function, driven largely by the role of the pathway initiating protein C1q. Given the links between C1q and cognitive function we assessed the genetic variability of the C1q encoding genes: C1QA, C1QB and C1QC between PD patients and matched controls. Despite a strong link between C1Q/cognitive decline and PD/cognitive decline we were unable to find a link between common C1Q variation and PD. We conclude that common C1Q-A/B/C genetic variation is unlikely to contribute to cognitive decline or the missing heritability in PD.

Interaction association analysis of imputed SNPs in case-control and follow-up studies

A new method is described to assess the interactions of imputed SNPs (single nucleotide polymorphisms) in case-control and follow-up studies, properly incorporating SNP imputation uncertainty in the likelihood model. Using simulation studies and analysis of real data obtained from the Framingham study cohort, we compare the performance of this new method to DOSAGE and NAIVE (also known as Best-Guess) methods, developed and commonly used in the context of single SNP and extended to SNP-by-SNP interaction. The results show that only our new method is unbiased under all examined scenarios regarding allele frequencies, imputation uncertainty degree, and interaction effect size. In addition, our method achieves at least as much power as the other two, and exceeds their statistical power in certain follow-up analysis situations. This method is fast enough to perform Genome Wide Interaction Studies (GWIS) with hundreds of thousands of interactions. By performing an exhaustive simulation study let us to provide recommendations for selecting the most appropriated method depending on MAF, interaction effect size, and uncertainty degree. In general, DOSAGE and our proposed method are recommended in most situations being our method more powerful and accurate when uncertainty and effect increase.

Identification of a novel non-coding mutation in C1qB in a Dutch child with C1q deficiency associated with recurrent infections

INTRODUCTION

C1q deficiency is a rare genetic disorder that is strongly associated with development of systemic lupus erythematosus (SLE). Several mutations in the coding regions of the C1q genes have been described that result in stop-codons or other genetic abnormalities ultimately leading to C1q deficiency. Here we report on a Dutch boy suffering from recurrent infections with a complete C1q deficiency, without any SLE symptoms.

METHODS

The presence of C1q in serum was assessed using ELISA and hemolytic assay. By western blot we examined the different C1q chains in cell lysates. We identified the mutation using deep-sequencing. By qPCR we studied the mRNA expression of C1qA, C1qB and C1qC in the PBMCs of the patient.

RESULTS

Deep-sequencing revealed a homozygous mutation in the non-coding region of C1qB in the patient, whereas both parents were heterozygous. The mutation is located two nucleotides before the splice site of the second exon. In-silico analyses predict a complete abrogation of this natural splice site. Analyses of in vitro cultured cells from the patient revealed a lack of production of C1q and intracellular absence of C1qB in the presence of C1qA and C1qC peptides. Quantitative PCR analysis revealed total absence of C1qB mRNA, a reduced level of C1qA mRNA and normal levels of C1qC mRNA.

CONCLUSION

In this study we report a new mutation in the non-coding region of C1qB that is associated with C1q deficiency.

Association of rs172378 C1q gene cluster polymorphism with lupus nephritis in Bulgarian patients

Introduction

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that can affect substantially any organ in the body. One of its most severe manifestations is lupus nephritis. Hereditary C1q deficiency is strongly related to SLE but there are very few and inconsistent studies exploring the single nucleotide polymorphisms (SNPs) of the C1q gene cluster in relation to the pathogenesis of SLE. In the present study we evaluated the possible association of gene variants in complement C1q gene cluster with susceptibility to lupus nephritis in a Bulgarian population, focusing on five previously associated with SLE SNPs in other populations.

Materials and methods

Thirty-eight patients with lupus nephritis and 185 healthy controls, all from Bulgaria, were genotyped for the five C1q SNPs, rs587585, rs292001, rs172378, rs294179 and rs631090, by quantitive real-time PCR methods. We also determined C1q serum levels of C1q and haemolytic activity of C1q in relation to C1q genotypes.

Results

Lupus nephritis patients and healthy controls had statistically similar frequencies of genotypes and alleles of rs587585, rs292001, rs294179 and rs631090 SNPs. Nevertheless, minor G allele in rs172378 was significantly overrepresented in lupus nephritis patients when compared with healthy controls (36% vs. 23%, odds ratio = 1.80, 95% confidence interval = 1.06–3.06, p = 0.029). The SNP rs292001 showed a trend towards lower serum C1q levels in healthy controls. Two SNPs – rs294179 and rs292001 – were in a linkage disequilibrium in patients and healthy controls with different power (healthy controls: r2 = 0.6526, D′ = 0.842; lupus nephritis patients: r2 = 0.491, D′ = 0.686). The haplotype C-A-A-T-T in the patient group was associated with lupus nephritis: 7.7% vs. 0.8%, odds ratio = 10.81, 95% confidence interval = 1.45–80.57, p = 0.002.

Conclusions

These results support the implication of the G allele in rs172378 as a risk factor for lupus nephritis in a homozygous status, at least for a Bulgarian population.

Relative contribution of c1q and apoptotic cell-surface calreticulin to macrophage phagocytosis

C1q has been shown to recognize apoptotic cells, to enhance their uptake and to modulate cytokine release by phagocytes and thus promote immune tolerance. Surface-exposed calreticulin (CRT), known as a C1q receptor, is also considered to be an early eat-me signal that enhances the phagocytosis of apoptotic cells and is capable of eliciting an immunogenic response. However, the molecular mechanisms that trigger these functions are not clear. We hypothesized that CRT and C1q might act together in these processes. We first showed, by means of fluorescence resonance energy transfer (FRET), that CRT interacts with the C1q globular region at the surface of early apoptotic cells. Next, we pointed out that knockdown of CRT on early apoptotic HeLa cells impairs the enhancement effect of C1q on their uptake by THP-1 monocyte-derived macrophages. Furthermore, a deficiency of CRT induces contrasting effects on cytokine release by THP-1 macrophages, increasing interleukin (IL)-6 and monocyte chemotactic protein 1/CCL2 and decreasing IL-8. Remarkably, these effects were greatly reduced when apoptotic cells were opsonized by C1q, which counterbalanced the effect of the CRT deficiency. These results demonstrate that CRT-C1q interaction is involved in the C1q bridging function and they highlight the particular ability of C1q to control the phagocyte inflammatory status, i.e. by integrating the molecular changes that could occur at the surface of dying cells.