Human Complement C4B Allotypes and Deficiencies in Selected Cases With Autoimmune Diseases

Decoding tryptophan: Pioneering new frontiers in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease that affects multiple organ systems, with its pathogenesis intricately tied to genetic, environmental, and immune regulatory factors. In recent years, the aberration of tryptophan metabolism has emerged as a key player in the disease, particularly through the activation of the kynurenine pathway and its influence on immune regulation. This review delves into the critical pathways of tryptophan metabolism and its profound impact on the multi-system manifestations of SLE, including its connections to the nervous system, kidneys, skin, and other organs. Additionally, it examines how tryptophan metabolism modulates the function of various immune cell types. The review also explores potential therapeutic avenues targeting tryptophan metabolism, such as dietary interventions, probiotic modulation, IDO expression inhibition, and immunoadsorption techniques. While current research has underscored the pivotal role of tryptophan metabolism in the onset and progression of SLE, its full therapeutic potential remains to be fully elucidated. This review aims to provide a solid scientific foundation for therapeutic strategies based on modulating tryptophan metabolism in SLE, offering a comprehensive overview of both clinical and basic research in this rapidly evolving field.

Anti-inflammatory properties of Pleione bulbocodioides extract through STING/ NF-κB pathway inhibition

The members of Pleione (Orchidaceae) are popular worldwide for their ornamental appeal and medicinal properties. Pleione bulbocodioides, a CITES Appendix II-listed species, has been traditionally used in dermatological therapies but remains pharmacologically understudied. In this study, the in vitro anti-inflammatory effects of extracts from artificially cultivated P. bulbocodioides were investigated. We found the P. bulbocodioides extract (PE) significantly suppressed TNF-α/IFN-γ-induced expression of IL-6, IL-1β, CCL5, CCL8, CXCL8, CXCL3, and TMEM173 (STING) genes in both HaCaT cells and NHEKs. Transcriptomic analysis and Western blotting confirmed the inhibitory effects on STING/NF-κB signaling pathway of PE. And phytochemical characterization identified militarine and batatasin III as principal bioactive constituents responsible for STING/NF-κB pathway inhibition by PE. PE also demonstrated comparable anti-inflammatory efficacy in LPS-induced RAW 264.7 macrophages and SLS-irritated 3D reconstructed human epidermis. Thus, these findings indicate the potential of PE as a natural anti-inflammatory therapeutic or skincare ingredient for dermatological applications.

Association of C4d with disease activity in anti-neutrophil cytoplasmic antibody-associated vasculitis: evidence for classical/lectin complement pathway activation

BACKGROUND

We aimed to investigate the involvement of the classical/lectin complement pathway in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) by exploring the complement activation fragment C4d in association to AAV activity.

METHODS

Forty patients with active AAV and twenty population-based controls were included. The study included 27 (67.5%) patients with a diagnosis of GPA and 13 (32.5%) with MPA. Twenty-four patients (60%) were anti-proteinase 3 (PR3)-ANCA positive and 16 (40%) anti-myeloperoxidase (MPO)-ANCA positive. Thirty-three (82.5%) patients had kidney involvement. A follow-up sample obtained after induction therapy (median 6 months) was available for 24 of the patients, of whom 20 were in remission. Plasma C4d was analysed by ELISA detecting an epitope that arises upon complement-mediated cleavage. Plasma complement factor 4 (C4) and the soluble terminal complement complex (sTCC) were analysed by ELISA. The C4d/C4 ratio was calculated. HLA-DRB1-typing and immunohistochemistry for C4d in kidney biopsies were performed.

RESULTS

Patients with active AAV had higher C4d, sTCC levels and C4d/C4 ratio than controls (p < 0.001, p = 0.004, p < 0.001). C4d, sTCC levels and C4d/C4 ratio all decreased from active disease to remission (p = 0.010, p = 0.009, p = 0.011). C4d levels in AAV patients in remission remained higher than population-based controls (p = 0.026). Active anti-PR3-ANCA patients had higher C4d levels and C4d/C4 ratio than anti-MPO-ANCA patients (p = 0.001, p = 0.007). Patients with active AAV and kidney involvement had lower C4d levels than patients without (p = 0.04). C4d levels and C4d/C4 ratio correlated positively with the percentage of normal glomeruli in kidney biopsies. The immunohistochemistry was negative for C4d in kidney biopsies.

CONCLUSIONS

The specific C4d assay revealed activity in the classical/lectin complement pathway in AAV, which reflected general disease activity, but was not associated specifically with kidney involvement. C4d levels differed depending on anti-PR3/MPO-ANCA subtypes suggesting differences in complement activation and underlying pathogenetic mechanisms. The findings imply that the classical/lectin complement pathway may play a more significant role in AAV pathogenesis than previously reported and that plasma C4d levels and C4d/C4 ratio may be biomarker candidates for disease activity and treatment outcome monitoring.

Investigation of the association between circulating inflammatory proteins and encephalitis risk in Europeans by two-sample Mendelian randomization analysis

Background

Cytokines are powerful immune response factors that operate at inflammation sites and are also found in the blood. Nevertheless, research on encephalitis and these circulating inflammatory proteins is quite limited.

Methods

This study investigated the potential causal effects of 91 circulating inflammatory proteins on three different types of encephalitis using a two-sample Mendelian randomisation analysis. The data source for encephalitis was the latest Finngen_R12 dataset, released in 2024. The study investigated causal effects mainly using Steiger, MR-Egger, weighted median and inverse variance weighting (IVW) methods. In addition, sensitivity analyses were performed, including heterogeneity assessment, horizontal pleiotropy and leave-one-out techniques.

Results

In this study, 91 circulating inflammatory proteins were subjected to MR analysis of causality with each of the three types of encephalitis. The results suggest that the inflammatory factors with a potential causal relationship with viral encephalitis are artemin, C-C motif chemokine 28, C-X-C motif chemokine 1, interleukin-10 and neurotrophin-3. Inflammatory factors potentially causally associated with acute disseminated encephalomyelitis are monocyte chemoattractant protein 2, interleukin-10 receptor subunit beta and matrix metalloproteinase-1. Inflammatory factors potentially causally associated with autoimmune encephalitis are C-C motif chemokine 28 levels and Macrophage inflammatory protein 1a levels.

Conclusion

This study identifies potential causal effects of certain circulating inflammatory factors on susceptibility to three types of encephalitis. Although the exact mechanisms by which inflammatory proteins contribute to the pathogenesis of different encephalitis subtypes remain unclear, our findings provide new perspectives on these potential causal relationships.

Causal relationship between circulating inflammatory proteins and risk of different types of encephalitis: A two-sample Mendelian randomization study

BACKGROUND

Cytokines are potent molecules of the immune response. They act at the site of inflammation and circulate in the bloodstream. However, there are few studies on encephalitis and circulating inflammatory proteins.

METHODS

In this study, Mendelian randomization (MR) was used to explore the potential causal effect of 91 circulating inflammatory proteins on 3 different types of encephalitis. Causal effects were examined using Steiger, MR-Egger, weighted median, and inverse variance weighting (IVW) methods. IVW methods were primarily used for results interpretation. In addition, sensitivity analyses were performed, including assessment of heterogeneity, horizontal pleiotropy, and Leave-one-out techniques.

RESULTS

We subjected 91 circulating inflammatory proteins to MR analysis of causality with each of the three types of encephalitis. The results suggested that the inflammatory factors with a potential causal relationship with viral encephalitis were caspase 8, C-X-C motif chemokine 6, interleukin-10, interleukin-15 receptor subunit alpha, interleukin-7, and TNF-beta. Inflammatory factors potentially causally associated with acute disseminated encephalomyelitis are beta-nerve growth factor, cystatin D, interleukin-7, Latency-associated peptide transforming growth factor beta 1,and neurotrophin-3.Inflammatory factors potentially causally associated with autoimmune encephalitis are C-C motif chemokine 25, hepatocyte growth factor, latency-associated peptide transforming growth factor beta 1, programmed cell death 1 ligand 1, sulfotransferase 1A1, and tumor necrosis factor.

CONCLUSION

This finding identifies potential causal effects of certain circulating inflammatory factors on susceptibility to three types of encephalitis. It also suggests the therapeutic potential of modulating the levels of these cytokines. A basis for further research is provided.

Genomic complexity and clinical significance of the RCCX locus

Nearly identical, repetitive elements in the genome contribute to the variability in genetic inheritance patterns, particularly in regions like the RCCX locus, where such repeats can lead to structural variations. In addition, during the formation of gametes as a result of meiosis, variants of loci with repetitive elements that do not code for the required proteins may occur. As a result, an individual with certain genetic rearrangements in this region may have an increased risk of developing a congenital disorder, particularly in cases where the non-functional allele is inherited dominantly. At the same time, there is still no routine or generally recognized diagnostic method to determine the sequence of the repetitive fragments. The functionally important RCCX locus consists of such repetitive fragments. The available knowledge about the genomic variants of the RCCX locus is fragmented, as there is no standardized method to determine its structure. It should be noted that in some structural variants of the RCCX locus, the sequence of protein-coding genes is disrupted, leading to the development of diseases such as congenital adrenal hyperplasia (CAH). Although genetic testing is generally accepted as a gold standard for CAH diagnosis, there are a myriad of strategies on which exact methods to use and in which order. The reason for this inconsistency lies in the complexity of the RCCX locus and the fact that each patient or carrier may have a highly individualized mutation or combination thereof. In this review, we have discussed all known methods that can be used to study the structure of the RCCX locus. As a result, optimal approaches are proposed for the diagnosis of the most common disease caused by lesions in the RCCX-CAH due to CYP21A2 deficiency.

Low C4A copy numbers and higher HERV gene insertion contributes to increased risk of SLE, with absence of association with disease phenotype and disease activity

Low copy numbers (CNs) of C4 genes are associated with systemic autoimmune disorders and affects autoantibody diversity and disease subgroups. The primary objective of this study was to characterize diversity of complement (C4) and C4-Human Endogenous Retrovirus (HERV) gene copy numbers in SLE. We also sought to assess the association of C4 and C4-HERV CNs with serum complement levels, autoantibodies, disease phenotypes and activity. Finally, we checked the association of C4 and HERV CNs with specific HLA alleles. Genomic DNA from 70 SLE and 90 healthy controls of south Indian Tamil origin were included. Demographic, clinical and serological data was collected in a predetermined proforma. CNs of C4A and C4B genes and the frequency of insertion of 6.4kb HERV within C4 gene (C4AL, C4BL) was determined using droplet digital polymerase chain reaction (ddPCR). A four digit high resolution HLA genotyping was done using next generation sequencing. In our cohort, the total C4 gene copies ranged from 2 to 6. Compared to controls, presence of two or less copies of C4A gene was associated with SLE risk (p = 0.005; OR = 2.79; 95% CI = 1.29-6.22). Higher frequency of HERV insertion in C4A than in C4B increases such risk (p = 0.000; OR = 12.67; 95% CI = 2.80-115.3). AL-AL-AL-BS genotype was significantly higher in controls than SLE (9%vs1%, p = 0.04; OR = 0.15, 95% CI = 0.00-0.16). Distribution of HLA alleles was not different in SLE compared to controls as well as in SLE subjects with ≤ 2 copies and > 2 copies of C4A, but HLA allele distribution was diverse in subjects with C4B ≤ 2 copies and > 2 copies. Finally, there was no correlation between the C4 and the C4-HERV diversity and complement levels, autoantibodies, disease phenotypes and activity. In conclusion, our data show that, low C4A copy number and higher insertion of HERV-K in C4A increases the risk for SLE. C4 and C4-HERV CNs did not correlate with serum complements, autoantibodies, disease phenotypes and activity in SLE. Further validation in a larger homogenous SLE cohort is needed.

Translating Molecular Approaches to Oligodendrocyte-Mediated Neurological Circuit Modulation

The central nervous system (CNS) exhibits remarkable adaptability throughout life, enabled by intricate interactions between neurons and glial cells, in particular, oligodendrocytes (OLs) and oligodendrocyte precursor cells (OPCs). This adaptability is pivotal for learning and memory, with OLs and OPCs playing a crucial role in neural circuit development, synaptic modulation, and myelination dynamics. Myelination by OLs not only supports axonal conduction but also undergoes adaptive modifications in response to neuronal activity, which is vital for cognitive processing and memory functions. This review discusses how these cellular interactions and myelin dynamics are implicated in various neurocircuit diseases and disorders such as epilepsy, gliomas, and psychiatric conditions, focusing on how maladaptive changes contribute to disease pathology and influence clinical outcomes. It also covers the potential for new diagnostics and therapeutic approaches, including pharmacological strategies and emerging biomarkers in oligodendrocyte functions and myelination processes. The evidence supports a fundamental role for myelin plasticity and oligodendrocyte functionality in synchronizing neural activity and high-level cognitive functions, offering promising avenues for targeted interventions in CNS disorders.

Increased risk of persistent neuropathic pain after traumatic nerve injury and surgery for carriers of a human leukocyte antigen haplotype

ABSTRACT

It is not known why some patients develop persistent pain after nerve trauma while others do not. Among multiple risk factors for the development of persistent posttrauma and postsurgical pain, a neuropathic mechanism due to iatrogenic nerve lesion has been proposed as the major cause of these conditions. Because there is some evidence that the human leukocyte antigen (HLA) system plays a role in persistent postsurgical pain, this study aimed to identify the genetic risk factors, specifically among HLA loci, associated with chronic neuropathic pain after traumatic nerve injuries and surgery in the upper extremities. Blood samples were taken to investigate the contribution of HLA alleles (ie, HLA-A, HLA-B, HLA-DRB1, HLA-DQB1, and HLA-DPB1) in a group of patients with persistent neuropathic pain (n = 70) and a group of patients with neuropathy without pain (n = 61). All subjects had intraoperatively verified nerve damage in the upper extremity. They underwent bedside clinical neurological examination to identify the neuropathic pain component according to the present grading system of neuropathic pain. Statistical analyses on the allele and haplotype were conducted using the BIGDAWG package. We found that the HLA haplotype A*02:01-B*15:01-C*03:04-DRB1*04:01-DQB1*03:02 was associated with an increased risk of developing persistent neuropathic pain in the upper extremity (OR = 9.31 [95% CI 1.28-406.45], P < 0.05). No significant associations were found on an allele level when correcting for multiple testing. Further studies are needed to investigate whether this association is on a haplotypic level or if certain alleles may be causing the association.

ptx3a+ fibroblast/epicardial cells provide a transient macrophage niche to promote heart regeneration

Macrophages conduct critical roles in heart repair, but the niche required to nurture and anchor them is poorly studied. Here, we investigated the macrophage niche in the regenerating heart. We analyzed cell-cell interactions through published single-cell RNA sequencing datasets and identified a strong interaction between fibroblast/epicardial (Fb/Epi) cells and macrophages. We further visualized the association of macrophages with Fb/Epi cells and the blockage of macrophage response without Fb/Epi cells in the regenerating zebrafish heart. Moreover, we found that ptx3a+ epicardial cells associate with reparative macrophages, and their depletion resulted in fewer reparative macrophages. Further, we identified csf1a expression in ptx3a+ cells and determined that pharmacological inhibition of the csf1a pathway or csf1a knockout blocked the reparative macrophage response. Moreover, we found that genetic overexpression of csf1a enhanced the reparative macrophage response with or without heart injury. Altogether, our studies illuminate a cardiac Fb/Epi niche, which mediates a beneficial macrophage response after heart injury.

Risk and protection of different rare protein-coding variants of complement component C4A in age-related macular degeneration

Introduction: Age-related macular degeneration (AMD) is the leading cause of central vision loss in the elderly. One-third of the genetic contribution to this disease remains unexplained. Methods: We analyzed targeted sequencing data from two independent cohorts (4,245 cases, 1,668 controls) which included genomic regions of known AMD loci in 49 genes. Results: At a false discovery rate of <0.01, we identified 11 low-frequency AMD variants (minor allele frequency <0.05). Two of those variants were present in the complement C4A gene, including the replacement of the residues that contribute to the Rodgers-1/Chido-1 blood group antigens: [VDLL1207-1210ADLR (V1207A)] with discovery odds ratio (OR) = 1.7 (p = 3.2 × 10-5) which was replicated in the UK Biobank dataset (3,294 cases, 200,086 controls, OR = 1.52, p = 0.037). A novel variant associated with reduced risk for AMD in our discovery cohort was P1120T, one of the four C4A-isotypic residues. Gene-based tests yielded aggregate effects of nonsynonymous variants in 10 genes including C4A, which were associated with increased risk of AMD. In human eye tissues, immunostaining demonstrated C4A protein accumulation in and around endothelial cells of retinal and choroidal vasculature, and total C4 in soft drusen. Conclusion: Our results indicate that C4A protein in the complement activation pathways may play a role in the pathogenesis of AMD.

High-throughput complement component 4 genomic sequence analysis with C4Investigator

The complement component 4 gene loci, composed of the C4A and C4B genes and located on chromosome 6, encodes for complement component 4 (C4) proteins, a key intermediate in the classical and lectin pathways of the complement system. The complement system is an important modulator of immune system activity and is also involved in the clearance of immune complexes and cellular debris. C4A and C4B gene loci exhibit copy number variation, with each composite gene varying between 0 and 5 copies per haplotype. C4A and C4B genes also vary in size depending on the presence of the human endogenous retrovirus (HERV) in intron 9, denoted by C4(L) for long-form and C4(S) for short-form, which affects expression and is found in both C4A and C4B. Additionally, human blood group antigens Rodgers and Chido are located on the C4 protein, with the Rodger epitope generally found on C4A protein, and the Chido epitope generally found on C4B protein. C4A and C4B copy number variation has been implicated in numerous autoimmune and pathogenic diseases. Despite the central role of C4 in immune function and regulation, high-throughput genomic sequence analysis of C4A and C4B variants has been impeded by the high degree of sequence similarity and complex genetic variation exhibited by these genes. To investigate C4 variation using genomic sequencing data, we have developed a novel bioinformatic pipeline for comprehensive, high-throughput characterization of human C4A and C4B sequences from short-read sequencing data, named C4Investigator. Using paired-end targeted or whole genome sequence data as input, C4Investigator determines the overall gene copy numbers, as well as C4A, C4B, C4(Rodger), C4(Ch), C4(L), and C4(S). Additionally, C4Ivestigator reports the full overall C4A and C4B aligned sequence, enabling nucleotide level analysis. To demonstrate the utility of this workflow we have analyzed C4A and C4B variation in the 1000 Genomes Project Data set, showing that these genes are highly poly-allelic with many variants that have the potential to impact C4 protein function.

High-throughput complement component 4 genomic sequence analysis with C4Investigator

The complement component 4 gene locus, composed of the C4A and C4B genes and located on chromosome 6, encodes for C4 protein, a key intermediate in the classical and lectin pathways of the complement system. The complement system is an important modulator of immune system activity and is also involved in the clearance of immune complexes and cellular debris. The C4 gene locus exhibits copy number variation, with each composite gene varying between 0-5 copies per haplotype, C4 genes also vary in size depending on the presence of the HERV retrovirus in intron 9, denoted by C4(L) for long-form and C4(S) for short-form, which modulates expression and is found in both C4A and C4B. Additionally, human blood group antigens Rodgers and Chido are located on the C4 protein, with the Rodger epitope generally found on C4A protein, and the Chido epitope generally found on C4B protein. C4 copy number variation has been implicated in numerous autoimmune and pathogenic diseases. Despite the central role of C4 in immune function and regulation, high-throughput genomic sequence analysis of C4 variants has been impeded by the high degree of sequence similarity and complex genetic variation exhibited by these genes. To investigate C4 variation using genomic sequencing data, we have developed a novel bioinformatic pipeline for comprehensive, high-throughput characterization of human C4 sequence from short-read sequencing data, named C4Investigator. Using paired-end targeted or whole genome sequence data as input, C4Investigator determines gene copy number for overall C4, C4A, C4B, C4(Rodger), C4(Ch), C4(L), and C4(S), additionally, C4Ivestigator reports the full overall C4 aligned sequence, enabling nucleotide level analysis of C4. To demonstrate the utility of this workflow we have analyzed C4 variation in the 1000 Genomes Project Dataset, showing that the C4 genes are highly poly-allelic with many variants that have the potential to impact C4 protein function.

Complement C4-deficient mice have a high mortality rate during PTZ-induced epileptic seizures, which correlates with cognitive problems and the deficiency in the expression of Egr1 and other immediate early genes

Complement system plays an important role in the immune defense against pathogens; however, recent studies demonstrated an important role of complement subunits C1q, C4, and C3 in normal functions of the central nervous system (CNS) such as non-functional synapse elimination (synapse pruning), and during various neurologic pathologies. Humans have two forms of C4 protein encoded by C4A and C4B genes that share 99.5% homology, while mice have only one C4B gene that is functionally active in the complement cascade. Overexpression of the human C4A gene was shown to contribute to the development of schizophrenia by mediating extensive synapse pruning through the activation C1q-C4-C3 pathway, while C4B deficiency or low levels of C4B expression were shown to relate to the development of schizophrenia and autism spectrum disorders possibly via other mechanisms not related to synapse elimination. To investigate the potential role of C4B in neuronal functions not related to synapse pruning, we compared wildtype (WT) mice with C3- and C4B- deficient animals for their susceptibility to pentylenetetrazole (PTZ)- induced epileptic seizures. We found that C4B (but not C3)-deficient mice were highly susceptible to convulsant and subconvulsant doses of PTZ when compared to WT controls. Further gene expression analysis revealed that in contrast to WT or C3-deficient animals, C4B-deficient mice failed to upregulate expressions of multiple immediate early genes (IEGs) Egrs1-4, c-Fos, c-Jus, FosB, Npas4, and Nur77 during epileptic seizures. Moreover, C4B-deficient mice had low levels of baseline expression of Egr1 on mRNA and protein levels, which was correlated with the cognitive problems of these animals. C4-deficient animals also failed to upregulate several genes downstream of IEGs such as BDNF and pro-inflammatory cytokines IL-1β, IL-6, and TNF. Taken together, our study demonstrates a new role of C4B in the regulation of expression of IEGs and their downstream targets during CNS insults such as epileptic seizures.

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.

Low copy numbers of complement C4 and C4A deficiency are risk factors for myositis, its subgroups and autoantibodies

BACKGROUND

Idiopathic inflammatory myopathies (IIM) are a group of autoimmune diseases characterised by myositis-related autoantibodies plus infiltration of leucocytes into muscles and/or the skin, leading to the destruction of blood vessels and muscle fibres, chronic weakness and fatigue. While complement-mediated destruction of capillary endothelia is implicated in paediatric and adult dermatomyositis, the complex diversity of complement C4 in IIM pathology was unknown.

METHODS

We elucidated the gene copy number (GCN) variations of total C4, C4A and C4B, long and short genes in 1644 Caucasian patients with IIM, plus 3526 matched healthy controls using real-time PCR or Southern blot analyses. Plasma complement levels were determined by single radial immunodiffusion.

RESULTS

The large study populations helped establish the distribution patterns of various C4 GCN groups. Low GCNs of C4T (C4T=2+3) and C4A deficiency (C4A=0+1) were strongly correlated with increased risk of IIM with OR equalled to 2.58 (2.28-2.91), p=5.0×10-53 for C4T, and 2.82 (2.48-3.21), p=7.0×10-57 for C4A deficiency. Contingency and regression analyses showed that among patients with C4A deficiency, the presence of HLA-DR3 became insignificant as a risk factor in IIM except for inclusion body myositis (IBM), by which 98.2% had HLA-DR3 with an OR of 11.02 (1.44-84.4). Intragroup analyses of patients with IIM for C4 protein levels and IIM-related autoantibodies showed that those with anti-Jo-1 or with anti-PM/Scl had significantly lower C4 plasma concentrations than those without these autoantibodies.

CONCLUSIONS

C4A deficiency is relevant in dermatomyositis, HLA-DRB1*03 is important in IBM and both C4A deficiency and HLA-DRB1*03 contribute interactively to risk of polymyositis.

Significance of urine complement proteins in monitoring lupus activity

Objectives

Complement activation is a critical feature in the development of systemic lupus erythematosus (SLE). Whether there are changes of complement components in the urine of SLE has not been reported. The aim of the study was to evaluate the complement-related proteins in the urine of SLE, verify differentially expressed proteins(DEPs) in the active phase of SLE, further explore their clinical application value.

Methods

First, we used bioinformatics and functional enrichment to screen and identify the urine protein profile of SLE patients. Then, analyzed and verified the proteins related to the complement pathway by western-blot and Parallel Reaction Monitoring (PRM) technology. Further evaluated the relationship between urinary DEPs related to complement pathway and disease activity.

Results

A total of 14 complement pathway-related proteins were screened for differences in expression between the active group and the stable group, eight of these DEPs were up-regulated and six were down-regulated. These DEPs may play a key role in SLE disease activity. We used PRM technology to verify the eight up-regulated proteins, and found that four of these complement proteins, namely C9, C8A, C4B, and C8G, were significantly increased in active group. Furthermore, these four DEPs were highly correlated with disease activity. In the urine of SLE patients, AUCs of 0.750, 0.840, 0.757 and 0.736 were achieved with C9, C8A, C4B, and C8G, respectively.

Conclusions

Complement-related DEPs in urine have a certain correlation with SLE disease activity. Urine C9, C8A, C4B and C8G present promising non-invasive biomarkers for monitoring lupus activity.