Identification of IgG subclasses and C-reactive protein in lupus nephritis: the relationship between the composition of immune deposits and FCgamma receptor type IIA alleles

Exploring the contribution of genetics on the clinical manifestations of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease characterized by diverse clinical manifestations affecting multiple organs and systems. The understanding of genetic factors underlying the various manifestations of SLE has evolved considerably in recent years. This review provides an overview of the genetic implications in some of the most prevalent manifestations of SLE, including renal involvement, neuropsychiatric, cutaneous, constitutional, musculoskeletal, and cardiovascular manifestations. We discuss the current state of knowledge regarding the genetic basis of these manifestations, highlighting key genetic variants and pathways implicated in their pathogenesis. Additionally, we explore the clinical implications of genetic findings, including their potential role in risk stratification, prognosis, and personalized treatment approaches for patients with SLE. Through a comprehensive examination of the genetic landscape of SLE manifestations, this review aims to provide insights into the underlying mechanisms driving disease heterogeneity and inform future research directions in this field.

Increased Immunoglobulin Gamma-3 Chain C in the Serum, Saliva, and Urine of Patients with Systemic Lupus Erythematosus

Immunoglobulin gamma-3 chain C (IGHG3) levels have been detected in the blood and tissue of patients with systemic lupus erythematosus (SLE). This study aims to assess its clinical value by measuring and comparing levels of IGHG3 in different body fluids in patients with SLE. The levels of IGHG3 in saliva, serum, and urine from 181 patients with SLE and 99 healthy controls were measured and analyzed. In patients with SLE and healthy controls, salivary IGHG3 levels were 3078.9 ± 2473.8 and 1413.6 ± 1075.3 ng/mL, serum IGHG3 levels were 478.1 ± 160.9 and 364.4 ± 97.9 μg/mL, and urine IGHG3 levels were 64.0 ± 74.5 and 27.1 ± 16.2 ng/mL, respectively (all p < 0.001). Salivary IGHG3 was correlated with ESR (correlation coefficient [r], 0.173; p = 0.024). Serum IGHG3 was correlated with leukocyte count (r, -0.219; p = 0.003), lymphocyte count (r, 0.22; p = 0.03), anti-dsDNA antibody positivity (r, 0.22; p = 0.003), and C3 levels (r, -0.23; p = 0.002). Urinary IGHG3 was correlated with hemoglobin level (r, -0.183; p = 0.021), ESR (r, 0.204; p = 0.01), anti-dsDNA antibody positivity (r, 0.262; p = 0.001), C3 levels (r, -0.202; p = 0.011), and SLE disease activity index (r, 0.332; p = 0.01). Urinary IGHG3 was higher in patients with nephritis than in those without (119.5 ± 110.0 vs. 49.8 ± 54.4 ng/mL; p < 0.01). IGHG3 was increased in the saliva, serum, and urine of patients with SLE. While salivary IGHG3 was not identified to be specific to SLE disease activity, serum IGHG3 showed correlations with clinical characteristics. Urinary IGHG3 levels were associated with disease activity and renal involvement in SLE.

Fc Gamma Receptors as Regulators of Bone Destruction in Inflammatory Arthritis

Bone erosion is one of the primary features of inflammatory arthritis and is caused by excessive differentiation and activation of osteoclasts. Fc gamma receptors (FcγRs) have been implicated in osteoclastogenesis. Our recent studies demonstrate that joint-deposited lupus IgG inhibited RANKL-induced osteoclastogenesis. FcγRI is required for RANKL-induced osteoclastogenesis and lupus IgG-induced signaling transduction. We reviewed the results of studies that analyzed the association between FcγRs and bone erosion in inflammatory arthritis. The analysis revealed the dual roles of FcγRs in bone destruction in inflammatory arthritis. Thus, IgG/FcγR signaling molecules may serve as potential therapeutic targets against bone erosion.

Distinct Effector B Cells Induced by Unregulated Toll-like Receptor 7 Contribute to Pathogenic Responses in Systemic Lupus Erythematosus

Systemic Lupus Erythematosus (SLE) is characterized by B cells lacking IgD and CD27 (double negative; DN). We show that DN cell expansions reflected a subset of CXCR5- CD11c+ cells (DN2) representing pre-plasma cells (PC). DN2 cells predominated in African-American patients with active disease and nephritis, anti-Smith and anti-RNA autoantibodies. They expressed a T-bet transcriptional network; increased Toll-like receptor-7 (TLR7); lacked the negative TLR regulator TRAF5; and were hyper-responsive to TLR7. DN2 cells shared with activated naive cells (aNAV), phenotypic and functional features, and similar transcriptomes. Their PC differentiation and autoantibody production was driven by TLR7 in an interleukin-21 (IL-21)-mediated fashion. An in vivo developmental link between aNAV, DN2 cells, and PC was demonstrated by clonal sharing. This study defines a distinct differentiation fate of autoreactive naive B cells into PC precursors with hyper-responsiveness to innate stimuli, as well as establishes prominence of extra-follicular B cell activation in SLE, and identifies therapeutic targets.

Antibodies targeting circulating protective molecules in lupus nephritis: Interest as serological biomarkers

Lupus nephritis (LN) is one of the most frequent and severe manifestations of systemic lupus erythematosus (SLE), considered as the major predictor of poor prognosis. An early diagnosis of LN is a real challenge in the management of SLE and has an important implication in guiding treatments. In clinical practice, conventional parameters still lack sensitivity and specificity for detecting ongoing disease activity in lupus kidneys and early relapse of nephritis. LN is characterized by glomerular kidney injury, essentially due to deposition of immune complexes involving autoantibodies against cellular components and circulating proteins. One of the possible mechanisms of induction of autoantibodies in SLE is a defect in apoptotic cells clearance and subsequent release of intracellular autoantigens. Autoantibodies against soluble protective molecules involved in the uptake of dying cells, including complement proteins and pentraxins, have been described. In this review, we present the main autoantibodies found in LN, with a focus on the antibodies against these protective molecules. We also discuss their pathogenic role and conclude with their potential interest as serological biomarkers in LN.

The relationship between anti-C-reactive protein and disease activity in patients with systemic lupus erythematosus

BACKGROUND/AIMS

Anti-C-reactive protein (CRP) antibody has been introduced as a potential biologic marker in Systemic lupus erythematosus (SLE). The aim of study is to evaluate the level of anti-CRP antibody in patients with SLE.

METHODS

This study investigated the relationship between levels of anti-CRP antibodies and disease activity markers, such as complement, anti-double-stranded DNA antibody, and SLE disease activity index in 34 patients with SLE.

RESULTS

The serum anti-CRP antibody levels of the patients with SLE were significantly higher than those of the healthy controls (11.3 ± 5.6 µg/mL vs. 9.1 ± 2.8 µg/mL). The percentages of the positive anti-CRP antibody were 52.9% in SLE and 27.8% in controls. Disease duration of SLE showed significant correlation with the anti-CRP antibody (r = 0.234, p = 0.026). However no significant relationship was observed between the levels of anti-CRP antibodies and disease activity markers.

CONCLUSIONS

These data show that the anti-CRP antibody levels of the patients with SLE were significantly higher than those of healthy controls. We observed that the presence of the anti-CRP anti-CRP antibody was not associated with disease activity of SLE.

Effects of a spleen tyrosine kinase inhibitor on progression of the lupus nephritis in mice

The Fc receptors (FcR) have pivotal roles in the pathogenesis of the autoimmune glomerulonephritis. We therefore investigated the effects of a Syk inhibitor on the progression of lupus nephritis and SH3 domain binding protein 2 and p38MAP kinase signalings in mice. NZB/W F1 mice, a model of lupus nephritis, received a Syk inhibitor R406. Western blotting and immunohistochemistry revealed that R406 treatment significantly delayed the appearance of proteinuria, histologically improved their glomerulosclerosis and inhibited the increased the expression of MCP-1 and TGF-β1 mRNAs and the nephrin and podocin proteins in the kidney. The treatment suppressed the phosphorylation of 3BP2 in white blood cells from the spleen and significantly inhibited the phosphorylation of p38MAPK in the kidney but did not affect expression of neonatal Fc receptor. These findings indicate the important roles and mechanisms of Fcγ receptors I and III in the development of autoimmune glomerulonephritis and suggest the possible application of Syk inhibitors as novel medicines for the glomerulonephritis.

Dissecting the relationships of IgG subclasses and complements in membranous lupus nephritis and idiopathic membranous nephropathy

Membranous lupus nephritis (MLN) and idiopathic membranous nephropathy (IMN) are kidney diseases with similar morphology, but distinct etiologies, both producing glomeruli with immune deposits. Immunoglobulins and complements, the main components of the deposits, can be detected by immunofluorescence (IF) microscopy. Previous researches characterized the immune deposits only individually, but not the interactions between them. To study these relationships we analyzed an IF profile of IgG subclasses and complements (IgG1, IgG2, IgG3, IgG4, C3, C1q, and C4) in 53 and 95 cases of biopsy-confirmed MLNs and IMNs, respectively, mainly using information theory and Bayesian networks. We identified significant entropy differences between MLN and IMN for all markers except C3 and IgG1, but mutual information (a measure of mutual dependence) were not significantly different for all the pairs of markers. The entropy differences between MLN and IMN, therefore, were not attributable to the mutual information. These findings suggest that disease type directly and/or indirectly influences the glomerular deposits of most of IgG subclasses and complements, and that the interactions between any pair of the markers were similar between the two diseases. A Markov chain of IgG subclasses was derived from the mutual information about each pair of IgG subclass. Finally we developed an integrated disease model, consistent with the previous findings, describing the glomerular immune deposits of the IgG subclasses and complements based on a Bayesian network using the Markov chain of IgG subclasses as seed. The relationships between the markers were effectively explored by information theory and Bayesian network. Although deposits of IgG subclasses and complements depended on both disease type and the other markers, the interaction between the markers appears conserved, independent from the disease type. The disease model provided an integrated and intuitive representation of the relationships of the IgG subclasses and complements in MLN and IMN.

Fc Gamma Receptor IIA (CD32A) R131 Polymorphism as a Marker of Genetic Susceptibility to Sepsis

Sepsis is a devastating disease that can affect humans at any time between neonates and the elderly and is associated with mortality rates that range from 30 to 80%. Despite intensive efforts, its treatment has remained the same over the last few decades. Fc receptors regulate multiple immune responses and have been investigated in diverse complex diseases. FcγRIIA (CD32A) is an immunoreceptor, tyrosine-based activation motif-bearing receptor that binds immunoglobulin G and C-reactive protein, important opsonins in host defense. We conducted a study of 702 patients (184 healthy individuals, 171 non-infected critically ill patients, and 347 sepsis patients) to investigate if genetic polymorphisms in the CD32A coding region affect the risk of septic shock. All individuals were genotyped for a variant at position 131 of the FcγRIIA gene. We found that allele G, associated with the R131 genotype, was significantly more frequent in septic patients than in the other groups (p = 0.05). Our data indicate that FcγRIIA genotyping can be used as a marker of genetic susceptibility to sepsis.

Genetics of human lupus nephritis

Systemic lupus erythematosus (SLE) is an inflammatory autoimmune disease characterized by immune complex formation with multi-organ manifestations. Lupus nephritis (LN) is one of the most severe types of organ damage in SLE, and it clearly contributes to increased morbidity and mortality due to SLE. LN occurs more frequently and is more severe in non-European ancestral backgrounds, although the cause of this disparity remains largely unknown. Genetic factors play an important role in the pathogenesis of SLE. Although many SLE susceptibility genes have been identified, the genetic basis of LN is not as well understood. While some of the established general SLE susceptibility genes are associated with LN, recent discoveries highlight a number of genes with renal functions that are specifically associated with LN. Some of these genes associated with LN help to explain the disparity in the prevalence of nephritis between individuals with SLE, and also partially explain differences in LN between ancestral backgrounds. Moreover, not only the gene mutations, but also post-translational modifications seem to play important roles in the pathogenesis of LN. Overall it seems likely that a combination of general SLE susceptibility genes cooperate with LN specific risk genes to result in the genetic propensity for LN. In this review, we will outline the genetic contribution to LN and describe possible roles of LN susceptibility genes.

Genetics of Lupus Nephritis: Clinical Implications

Systemic lupus erythematosus is a heterogeneous autoimmune disease marked by the presence of pathogenic autoantibodies, immune dysregulation, and chronic inflammation that may lead to increased morbidity and early mortality from end-organ damage. More than half of all systemic lupus erythematosus patients will develop lupus nephritis. Genetic-association studies have identified more than 50 polymorphisms that contribute to lupus nephritis pathogenesis, including genetic variants associated with altered programmed cell death and defective immune clearance of programmed cell death debris. These variants may support the generation of autoantibody-containing immune complexes that contribute to lupus nephritis. Genetic variants associated with lupus nephritis also affect the initial phase of innate immunity and the amplifying, adaptive phase of the immune response. Finally, genetic variants associated with the kidney-specific effector response may influence end-organ damage and the progression to end-stage renal disease and death. This review discusses genetic insights of key pathogenic processes and pathways that may lead to lupus nephritis, as well as the clinical implications of these findings as they apply to recent advances in biologic therapies.

IgG Subclass Staining in Routine Renal Biopsy Material

Immunofluorescence staining plays a vital role in nephropathology, but the panel of antibodies used has not changed for decades. Further classification of immunoglobulin (Ig)G-containing immune-type deposits with IgG subclass staining (IgG1, IgG2, IgG3, and IgG4) has been shown to be of diagnostic utility in glomerular diseases, but their value in the evaluation of renal biopsies has not been addressed systematically in large renal biopsy material. Between January 2007 and June 2014, using direct immunofluorescence, we stained every renal biopsy for the IgG subclasses if there was moderate to prominent glomerular IgG staining and/or IgG-predominant or IgG-codominant glomerular staining. The total number of biopsies stained was 1084, which included 367 cases of membranous glomerulonephritis, 307 cases of lupus nephritis, 74 cases of fibrillary glomerulonephritis, 53 cases of proliferative glomerulonephritis with monoclonal IgG deposits, and 25 cases of antiglomerular basement membrane disease, among others. We found that monoclonality of IgG deposits cannot always be reliably determined on the basis of kappa and lambda light chain staining alone, particularly if concomitant (frequently nonspecific) IgM staining is present. In IgG heavy and heavy and light chain deposition disease (3 cases), subclass staining is very helpful, and in proliferative glomerulonephritis with monoclonal IgG deposits subclass staining is necessary. IgG subclass staining is useful in differentiating primary from secondary membranous glomerulonephritis. In proliferative glomerulonephritis with polyclonal IgG deposition, IgG1 dominance/codominance with concomitant IgG3 and IgG2 but weak or absent IgG4 staining favors an underlying autoimmune disease. IgG subclass staining is a very useful diagnostic method in a selected cohort of renal biopsies, particularly in biopsies with glomerulonephritis with monoclonal IgG deposits.

High sensitivity C-reactive protein in systemic lupus erythematosus: relation to disease activity, clinical presentation and implications for cardiovascular risk

Measurement of high sensitivity C-reactive protein (hs-CRP), has been used in the assessment of disease activity in numerous rheumatic conditions including systemic lupus erythematosus (SLE). However, the utility of hs-CRP measurement in patients with lupus is uncertain. This study examined if hs-CRP can be used to assess disease activity, severity and cardiovascular risk in SLE. Serum samples from 601 visits of 213 SLE patients and 134 controls were analysed for hs-CRP by nephelometry. Detailed demographic data were obtained from all subjects and medication history and key laboratory parameters were collected. Disease activity was assessed using the SLEDAI. High sensitivity CRP was not associated with disease activity (SLEDAI), number of ACR SLE criteria or presence of any particular organ involvement. hs-CRP levels were significantly correlated with standard cardiovascular risk factors including body weight ( P = 0.0002), hypertension ( P = 0.001), and apolipoprotein A-I ( P < 0.0001). Interestingly an inverse correlation was seen between hs-CRP levels and antimalarial use ( P = 0.0018). Our results suggest that measurement of hs-CRP, though not valuable as marker of disease activity in SLE may be of some use in the assessment of cardiovascular risk. We speculate that antimalarials may help to reduce cardiovascular risk in patients with SLE.

Clinical disease activity and titers of anti-dsDNA antibodies measured by an automated immunofluorescence assay in patients with systemic lupus erythematosus

Autoantibodies specific for double stranded DNA (anti-dsDNA Abs) are a serological biomarker of systemic lupus erythematosus (SLE) and constitute useful tools for monitoring many SLE patients. A new automated immunofluorescence and quantitative assay (EliA dsDNA) has recently become available. Its performance has been demonstrated to be equivalent to the Farr and Crithidia luciliae fluorescence (CLIFT) tests. The aim of the present work was to assess the utility of this new assay to monitor clinical activity in a large cohort of SLE patients. To this end, 1020 sera from 181 SLE patients were evaluated by the two methods. Results showed a higher frequency of positive results of anti-dsDNA Abs during lupus flares measured by EliA dsDNA than by CLIFT. Likewise, titers of those Abs were significantly increased in active SLE in comparison with inactive SLE when measured by EliA dsDNA but not by CLIFT. Serum titers of anti-dsDNA Abs by both assays showed a significant negative association with concentrations of C3 and C4. In summary, this retrospective study on a large cohort of patients demonstrated that EliA dsDNA was at least as useful as CLIFT as monitoring tool in the follow-up of SLE patients, but with the advantages of being automated, quick and quantitative.

Prognostic value of anti-CRP antibodies in lupus nephritis in long-term follow-up

Background

Autoantibodies against monomeric C-reactive protein (anti-CRP-Ab) observed in patients with systemic lupus erythematosus (SLE) and lupus nephritis (LN) were suggested to be associated with active LN and a poor response to therapy during short-term follow-up.

The aim of this study was to confirm this finding and to investigate the prognostic value of anti-CRP-Ab in patients with LN during long-term follow-up.

Methods

Sera of 57 SLE patients (47 women, 10 men) with biopsy proven LN and 122 healthy individuals were analyzed for the presence of anti-CRP-Ab by in-house ELISA.

Anti-CRP-Ab levels were studied in relation to routine laboratory tests, urine analysis, levels of C3, C4, other immunological markers and the overall disease activity as assessed by Systemic Lupus Erythematosus Disease Activity Index (SLEDAI).

The prognostic value of anti-CRP-Ab was tested in a subgroup of 29 newly diagnosed LN patients (median follow-up 5.9 years). Response to therapy at various time points was assessed with respect to baseline anti-CRP-Ab levels. At least partial response in the first/second year of treatment was considered as a “favorable outcome”, while non-response, renal flare or end stage renal disease were considered as “unfavorable outcome”.

Results

Anti-CRP-Ab were only detected in patients with active renal disease and their levels correlated with SLEDAI (r_s = 0.165, p = 0.002). The time to response was shorter in patients being anti-CRP-Ab negative at baseline compared to anti-CRP-Ab positive patients, p = 0.037. In the second year of therapy, baseline anti-CRP-Ab positivity was a significant predictor of “unfavorable outcome” (OR [95 % CI] = 15.6 [1.2-771]; p = 0.021). The predictive value of “baseline anti-CRP positivity” further increased when combined with “non-response to therapy in the first year”. Baseline anti-CRP-Ab positivity was not a predictor of “unfavorable outcome” at the end of follow-up, (OR [95 % CI] = 5.5 [0.6-71.1], p = 0.169).

Conclusions

Baseline serum levels of anti-CRP-Ab seem to be a strong risk factor for a composite outcome of non-response, renal flare or end stage renal disease after two years of standard treatment of LN. The response to therapy seems to be delayed in anti-CRP-Ab positive patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0879-8) contains supplementary material, which is available to authorized users.

Autoantibodies to C-reactive protein in incomplete lupus and systemic lupus erythematosus

OBJECTIVE

Anti-C-reactive protein (CRP) antibodies have been described in patients with systemic lupus erythematosus (SLE). We investigated the potential of the anti-CRP antibody as a marker for disease activity in SLE patients and as a predictor of progression to SLE in patients with incomplete lupus.

METHODS

Immunoglobulin G anti-CRP antibody levels were measured using an enzyme-linked immunosorbent assay.

RESULTS

Patients with incomplete lupus exhibited clinical and immunologic characteristics different from those in SLE patients: no serositis and alopecia, more common oral ulcers and arthritis, lower disease activity index, lower positivity for antinuclear and anti-double-strand DNA antibodies, and higher complement levels. Anti-CRP antibody levels were higher in SLE patients (35.6 [35.1] AU) than in patients with incomplete lupus (23.1 [25.8] AU, P = 0.016) and normal controls (21.0 [14.3] AU, P < 0.001). Anti-CRP antibody was significantly higher in SLE patients with arthritis and correlated with disease activity markers, including antichromatin antibody. However, no difference in anti-CRP antibody levels was observed between patients with incomplete lupus that progressed to SLE and those whose did not.

CONCLUSION

These data suggest that anti-CRP antibodies can neither be used as biomarkers in SLE nor predict SLE progression in patients with incomplete lupus.

Fcγ receptors and ligands and cardiovascular disease

Fcγ receptors (FcγRs) classically modulate intracellular signaling on binding of the Fc region of IgG in immune response cells. How FcγR and their ligands affect cardiovascular health and disease has been interrogated recently in both preclinical and clinical studies. The stimulation of activating FcγR in endothelial cells, vascular smooth muscle cells, and monocytes/macrophages causes a variety of cellular responses that may contribute to vascular disease pathogenesis. Stimulation of the lone inhibitory FγcR, FcγRIIB, also has adverse consequences in endothelial cells, antagonizing NO production and reparative mechanisms. In preclinical disease models, activating FcγRs promote atherosclerosis, whereas FcγRIIB is protective, and activating FcγRs also enhance thrombotic and nonthrombotic vascular occlusion. The FcγR ligand C-reactive protein (CRP) has undergone intense study. Although in rodents CRP does not affect atherosclerosis, it causes hypertension and insulin resistance and worsens myocardial infarction. Massive data have accumulated indicating an association between increases in circulating CRP and coronary heart disease in humans. However, Mendelian randomization studies reveal that CRP is not likely a disease mediator. CRP genetics and hypertension warrant further investigation. To date, studies of genetic variants of activating FcγRs are insufficient to implicate the receptors in coronary heart disease pathogenesis in humans. However, a link between FcγRIIB and human hypertension may be emerging. Further knowledge of the vascular biology of FcγR and their ligands will potentially enhance our understanding of cardiovascular disorders, particularly in patients whose greater predisposition for disease is not explained by traditional risk factors, such as individuals with autoimmune disorders.

IRF5-mediated signaling and implications for SLE

Transcription of the type I IFN genes is regulated by members of the Interferon Regulatory Factor (IRF) family of transcription factors, composed in humans of 9 distinct proteins. In addition to IRF3 and IRF7, the transcription factor IRF5 has been shown to be involved in type I IFN production and interestingly, polymorphisms of the IRF5 gene in humans can result in risk or protective haplotypes with regard to SLE susceptibility. In addition to regulation of type I IFN expression, IRF5 is involved in other signaling pathways, including IgG switching in B cells, macrophage polarization and apoptosis, and its role in SLE pathogenesis may therefore not be limited to dysregulated control of IFN expression. In this review we will comprehensively discuss the role of IRF5 in immune-mediated responses and its potential multifaceted role in conferring SLE susceptibility.

The proinflammatory effect of C-reactive protein on human endothelial cells depends on the FcγRIIa genotype

INTRODUCTION

The stimulatory effects of CRP (C-reactive protein) on endothelial cells are mainly mediated via FcγRIIa. This receptor exists in two different allotypes bearing either arginine (R131) or histidine (H131) at the extracellular amino acid position 131 of the mature protein, but only FcγRIIa-R131 displays high avidity for CRP. This study investigated the role of the FcγRIIa genotype in CRP-stimulated endothelial cells.

MATERIALS AND METHODS

We tested the effects of CRP on expression of the adhesion molecules ICAM-1, VCAM-1, and E-selectin, as well as the endothelial release of pro-inflammatory molecules as a function of the FcγRIIa-genotype (FcγRIIa-H/H131, FcγRIIa-H/R131, FcγRIIa-R/R131) in HUVEC (Human Umbilical Vein Endothelial Cells). HUVEC were grouped according to their FcγRIIa status by genotyping with an allele specific nested-PCR. The expression of ICAM-1, VCAM-1, and E-selectin on HUVEC was detected by flow cytometry. The release of soluble markers (sCD40L, IL-6, IL-8, MCP-1, tPA, sP-selectin, and sVCAM-1) was measured using a multiplex assay for flow cytometry.

RESULTS AND CONCLUSIONS

CRP-stimulated expression of ICAM-1 and E-selectin was dependent on the specific FcγRIIa-genotype, with most pronounced induction in HUVEC with the FcγRIIa-R/R genotype, followed by H/R and H/H. In accordance with this finding, the supernatants of stimulated HUVEC with the R/R genotype showed significantly higher levels of tPA, MCP-1, and IL-6. Our data show that CRP stimulates the expression of adhesion molecules and the release of soluble markers by HUVEC as a function of the FcγRIIa-genotype. These findings could be relevant in the context of risk stratification in patients with cardiovascular disease.

Prognostic factors for treatment response in patients with lupus nephritis

OBJECTIVE

To identify prognostic factors associated with response to induction therapy in lupus nephritis (LN) according to the stage of treatment.

MATERIAL AND METHODS

We analyzed a retrospective cohort of patients of systemic lupus erythematosus (SLE) with biopsy-proven LN from January 2001 to December 2008. LN was classified according to WHO. All patients received induction therapy and had a minimum follow-up period of two years. We analyzed 18 clinical and laboratory variables that potentially have predictive value for response to therapy. We identified predictors of therapeutic response at 6, 12 and 24 months by univariate and multivariate analysis; odds ratios (OR) with confidence intervals (CI) 95% were also calculated.

RESULTS

We reviewed the clinical records of 168 patients, 141 female (84%). The response rate was 69% at 6 months, 86.9% at 12 months and 79.7% at 24 months. Multivariate analysis found that > 25 years of age at diagnosis of LN and the presence of microhematuria were factors associated with good response to induction treatment. At 12 months, baseline creatinine clearance < 30ml/min was associated with a poor response to treatment. Finally at 24 months, delay in treatment was a predictor of poor response to treatment and the presence of a histological proliferative NL and low C3 were associated with good response to treatment.

CONCLUSIONS

There are treatment-modifiable factors that can alter aberrant immunologic activity of NF. Therefore, intensive early treatment of lupus nephritis is associated with favorable response to two years.

Pentraxins: structure, function, and role in inflammation

The pentraxins are an ancient family of proteins with a unique architecture found as far back in evolution as the Horseshoe crab. In humans the two members of this family are C-reactive protein and serum amyloid P. Pentraxins are defined by their sequence homology, their pentameric structure and their calcium-dependent binding to their ligands. Pentraxins function as soluble pattern recognition molecules and one of the earliest and most important roles for these proteins is host defense primarily against pathogenic bacteria. They function as opsonins for pathogens through activation of the complement pathway and through binding to Fc gamma receptors. Pentraxins also recognize membrane phospholipids and nuclear components exposed on or released by damaged cells. CRP has a specific interaction with small nuclear ribonucleoproteins whereas SAP is a major recognition molecule for DNA, two nuclear autoantigens. Studies in autoimmune and inflammatory disease models suggest that pentraxins interact with macrophage Fc receptors to regulate the inflammatory response. Because CRP is a strong acute phase reactant it is widely used as a marker of inflammation and infection.

Pentraxins and Fc receptors

Pentraxins are innate pattern recognition molecules whose major function is to bind microbial pathogens or cellular debris during infection and inflammation and, by doing so, contribute to the clearance of necrotic cells as well as pathogens through complement activations. Fc receptors are the cellular mediators of antibody functions. Although conceptually separated, both pentraxins and antibodies are important factors in controlling acute and chronic inflammation and infections. In recent years, increasing experimental evidence suggests a direct link between the innate pentraxins and humoral Fc receptors. Specifically, both human and mouse pentraxins recognize major forms of Fc receptors in solution and on cell surfaces with affinities similar to antibodies binding to their low affinity Fc receptors. Like immune complex, pentraxin aggregation and opsonization of pathogen result in Fc receptor and macrophage activation. The recently published crystal structure of human serum amyloid P (SAP) in complex with FcγRIIA further illustrated similarities to antibody recognition. These recent findings implicate a much broader role than complement activation for pentraxins in immunity. This review summarizes the structural and functional work that bridge the innate pentraxins and the adaptive Fc receptor functions. In many ways, pentraxins can be regarded as innate antibodies.

Differential diagnosis of lupus and primary membranous nephropathies by IgG subclass analysis

BACKGROUND AND OBJECTIVES

Previous studies showed that the accuracy of IgG subclasses (ISs) in differentiating membranous lupus nephritis (MLN) from primary membranous nephropathy (PMN) is <80%. This study hypothesized that diagnostic accuracy of ISs would be increased if renal compartment measurements and decision tree analysis are applied.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Renal biopsy specimens from 41 patients with MLN and 59 patients with PMN between October 2004 and March 2010 were examined, and immunofluorescence staining against IgG1, IgG2, IgG3, and IgG4 as well as C3, C1q, and C4 was evaluated in five different renal compartments (glomerular capillary walls, mesangium, tubules, interstitium, and blood vessels). From IS data, a decision tree to differentiate MLN from PMN was produced (IS decision tree) and its accuracy was compared with that of previous studies. Diagnostic accuracy of the IS decision tree was also compared with that of the complement decision tree as a reference.

RESULTS

The demographic information and patterns of IS deposition were similar to those of previous studies. The IS decision tree had, as decision markers, IgG1 in the mesangium and IgG2 and IgG4 along the glomerular capillary wall. The IS decision tree showed higher accuracy (88%) than that of previous studies (<80%) and also that of the complement decision tree (81%).

CONCLUSIONS

Accuracy of ISs was increased due to the study methods, but the same methodology was less effective using complement measurements. Appropriate data analysis may enhance diagnostic value, but the analysis alone cannot achieve the ideal diagnostic value.

Patients with unstable angina pectoris show an increased frequency of the Fc gamma RIIa R131 allele

Patients with Systemic Lupus Erythematosus (SLE) carry an increased risk for the development of coronary artery disease (CAD). The R131 allele of the Fc gamma receptor IIa (FcγRIIa) is associated with SLE incidence and disease severity but also with CAD. Compared to stable angina pectoris (SAP) the unstable angina (UAP), as a manifestation of destabilizing CAD, is associated with increased risk of persistent instability, myocardial infarction, and death. Identification of clinically relevant determinants for unstable angina promises reduction of UAP-associated mortality in patients with SLE. We conducted a clinical study among 553 consecutive patients with stable angina pectoris (n = 330) and unstable angina pectoris (n = 223). All patients were genotyped for a frequent functional variant at position 131 of the mature FcγRIIa. UAP, but not SAP was significantly associated with the R/R131 genotype (P < 0.001). In troponin-negative patients with angina carrying the R/R131 genotype the odds ratio for suffering from UAP was 4.02 (95% confidence interval, 2.52-6.41) compared to those with non-R/R131 genotypes. In a multivariable analysis, the R/R131 genotype independently predicted the risk for development of UAP in a model adjusted for classical atherogenic risk factors. Our data imply that risk stratification of SLE- and other high risk patients with troponin-negative angina could be significantly improved by FcγRIIa genotyping.

High prevalence of autoantibodies to C-reactive protein in patients with chronic hepatitis C infection: association with liver fibrosis and portal inflammation

The presence of autoantibodies against C-reactive protein (anti-CRP) has been reported in association with autoimmunity and histopathology in chronic hepatitis C virus (HCV) infection. Resistin could play a role in the pathogenesis of hepatitis, although results on HCV infection are ambiguous. Here we retrospectively analyzed anti-CRP and resistin levels in the sera of 38 untreated and well-characterized HCV patients at the time of their first liver biopsy. HCV activity and general health were assessed by a physician at least yearly until follow-up ended. Anti-CRP and resistin were also measured in patients with autoimmune hepatitis (AIH) and nonalcoholic fatty liver disease (NAFLD). Anti-CRP antibodies were registered in all HCV patients, whereas only a few AIH (11%) and NAFLD (12%) sera were positive. Anti-CRP levels were related to histopathological severity and were highest in patients with cirrhosis at baseline. Resistin levels were similar in HCV, AIH, and NAFLD patients, but high levels of resistin were associated with early mortality in HCV patients. Neither anti-CRP nor resistin predicted a response to interferon-based therapy or cirrhosis development or was associated with liver-related mortality. We conclude that anti-CRP antibodies are frequently observed in chronic HCV infection and could be a useful marker of advanced fibrosis and portal inflammation.

Progesterone and autoimmune disease

Sexual dimorphism in human immune systems is most apparent in the female predominance of certain autoimmune diseases (ADs) like systemic lupus erythematosus (SLE). Epidemiologic, observational and experimental evidence strongly suggest sex steroids are important modulators of genetic risk in human AD. In this regard, the roles of progesterone (Pg), an immunomodulatory female sex steroid, are poorly understood. Several lines of investigation indicate Pg and synthetic progestins impact risk of AD and immune-mediated injury in different ways depending on their concentrations and their engagement of various Pg receptors expressed in immune organs, immune cells or tissues targeted by immune attack. At low physiologic levels, Pg may enhance interferon-alpha (IFN-α) pathways important in SLE pathogenesis. Commonly used synthetic progestins may have the opposite effect. At pregnancy levels, Pg may suppress disease activity in rheumatoid arthritis (RA) and multiple sclerosis (MS) via inhibition of T helper type 1 (Th1) and Th17 pathways and induction of anti-inflammatory molecules. Importantly, Pg's immunomodulatory effects differ from those of estrogens and androgens. An additional layer of complexity arises from apparent interdependence of sex hormone signaling pathways. Identifying mechanisms by which Pg and other sex steroids modulate risk of AD and immune-mediated injury will require clarification of their cellular and molecular targets in vivo. These future studies should be informed by recent genetic discoveries in human AD, particularly those revealing their sex-specific genetic associations.

Distribution of glomerular IgG subclass deposits in patients with membranous nephropathy and anti-U1 ribonucleoprotein antibody

BACKGROUND

It is known that a predominant glomerular deposition of IgG4 is characteristic of idiopathic membranous nephropathy (MN) and that significant deposition of other IgG subclasses is also observed in lupus MN. However, there is no report focusing on the distribution of glomerular IgG subclass deposits in MN patients with anti-U1 ribonucleoprotein (RNP) antibody.

METHODS

We evaluated clinicopathological features and the distribution patterns of glomerular IgG subclass deposits in seven MN patients with positive anti-RNP antibody and negative antibodies to double-stranded DNA (dsDNA) and Smith antigen (Sm) (RNP-MN group) and in seven age- and sex-matched lupus MN patients with positive anti-dsDNA antibody and negative antibodies to RNP and Sm (L-MN group).

RESULTS

Mixed connective tissue disease was diagnosed in four patients in the RNP-MN group. Two patients in the RNP-MN group and three patients in the L-MN group developed nephrotic syndrome. Renal insufficiency was not present in all patients in both groups. Hypocomplementemia was found in two patients in the RNP-MN group and six patients in the L-MN group. In the RNP-MN group, positive stainings for glomerular IgG1, IgG2, IgG3 and IgG4 were observed in one, seven, zero and five patients, respectively. On the contrary, in the L-MN group, positive stainings for glomerular IgG1, IgG2, IgG3 and IgG4 were observed in seven, seven, seven, and six patients, respectively.

CONCLUSIONS

This is the first study showing striking differences in the distribution of glomerular IgG subclass deposits between RNP-MN and L-MN groups. RNP-MN and L-MN may result from different immunological mechanisms.

Structural basis for Fc gammaRIIa recognition of human IgG and formation of inflammatory signaling complexes

The interaction of Abs with their specific FcRs is of primary importance in host immune effector systems involved in infection and inflammation, and are the target for immune evasion by pathogens. FcγRIIa is a unique and the most widespread activating FcR in humans that through avid binding of immune complexes potently triggers inflammation. Polymorphisms of FcγRIIa (high responder/low responder [HR/LR]) are linked to susceptibility to infections, autoimmune diseases, and the efficacy of therapeutic Abs. In this article, we define the three-dimensional structure of the complex between the HR (arginine, R134) allele of FcγRIIa (FcγRIIa-HR) and the Fc region of a humanized IgG1 Ab, hu3S193. The structure suggests how the HR/LR polymorphism may influence FcγRIIa interactions with different IgG subclasses and glycoforms. In addition, mutagenesis defined the basis of the epitopes detected by FcR blocking mAbs specific for FcγRIIa (IV.3), FcγRIIb (X63-21), and a pan FcγRII Ab (8.7). The epitopes detected by these Abs are distinct, but all overlap with residues defined by crystallography to contact IgG. Finally, crystal structures of LR (histidine, H134) allele of FcγRIIa and FcγRIIa-HR reveal two distinct receptor dimers that may represent quaternary states on the cell surface. A model is presented whereby a dimer of FcγRIIa-HR binds Ag-Ab complexes in an arrangement that possibly occurs on the cell membrane as part of a larger signaling assembly.

High-sensitivity C-reactive protein and erythrocyte sedimentation rate in systemic lupus erythematosus

Levels of C-reactive protein (CRP) have been shown to rise in acute illnesses such as infections and some autoimmune diseases, but not in flares of systemic lupus erythematosus (SLE). Our goal was to investigate the high-sensitivity CRP (hsCRP) response to infection versus disease flare in patients with SLE, and to compare this with the erythrocyte sedimentation rate (ESR) response in these patients. We aimed to determine the hsCRP level that distinguishes between infection and flare in SLE, and investigated the correlation between hsCRP and organ involvement in SLE. We reviewed electronic medical records of all patients with SLE admitted to Cedars Sinai Medical Center between 28 August 2001 and 27 April 2008. Patients were divided into three groups based on the reason for hospitalization: 1) lupus flare; 2) active infection; and 3) both lupus flare and active infection. Data were collected on patient demographics, medication use, microbial culture results, organ involvement in lupus flare, ESR and CRP levels. Data were collected on 85 eligible patients, of whom 54 had a lupus flare, 22 had active infection and eight had both. While the ESR levels did not differ significantly between patients with disease flare and active infection, the hsCRP level was significantly lower in the lupus flare group than in the infection group. Most patients in the lupus flare group who had a significantly high hsCRP level had serositis. We found that at a cut-off of above 5 mg/dl, hsCRP level was correlated with infection with a specificity of 80%. At a cut-off of above 6 mg/dl, hsCRP correlated with infection with a specificity of 84%. hsCRP level was found to be significantly higher in patients with pulmonary involvement than without. hsCRP levels are significantly lower in SLE patients with disease flare than in those with active infection. Elevated hsCRP levels can be used as a predictor of active infection in SLE patients with a high specificity. We review the relationship between IL-6 and hsCRP production in lupus patients.

Genetic susceptibility to systemic lupus erythematosus in the genomic era

Our understanding of the genetic basis of systemic lupus erythematosus (SLE) has been rapidly advanced using large-scale, case-control, candidate gene studies as well as genome-wide association studies during the past 3 years. These techniques have identified more than 30 robust genetic associations with SLE including genetic variants of HLA and Fcγ receptor genes, IRF5, STAT4, PTPN22, TNFAIP3, BLK, BANK1, TNFSF4 and ITGAM. Most SLE-associated gene products participate in key pathogenic pathways, including Toll-like receptor and type I interferon signaling pathways, immune regulation pathways and those that control the clearance of immune complexes. Disease-associated loci that have not yet been demonstrated to have important functions in the immune system might provide new clues to the underlying molecular mechanisms that contribute to the pathogenesis or progression of SLE. Of note, genetic risk factors that are shared between SLE and other immune-related diseases highlight common pathways in the pathophysiology of these diseases, and might provide innovative molecular targets for therapeutic interventions.

Dynamics of the interaction of human IgG subtype immune complexes with cells expressing R and H allelic forms of a low-affinity Fc gamma receptor CD32A

CD32A, the major phagocytic FcgammaR in humans, exhibits a polymorphism in the ligand binding domain. Individuals homozygous for the R allelic form of CD32A (CD32A(R) allele) are more susceptible to bacterial infections and autoimmune diseases as compared with H allelic CD32A (CD32A(H)) homozygous and CD32A(R/H) heterozygous individuals. To understand the mechanisms behind this differential susceptibility, we have investigated the dynamics of the interaction of these allelic forms of CD32A when they are simultaneously exposed to immune complexes (IC). Binding studies using Ig fusion proteins of CD32A alleles showed that the R allele has significantly lower binding not only to human IgG2, but also to IgG1 and IgG3 subtypes. Competition assays using purified molecules demonstrated that CD32A(H)-Ig outcompetes CD32A(R)-Ig for IC binding when both alleles simultaneously compete for the same ligand. CD32A(H)-Ig blocked the IC binding mediated by both the allelic forms of cell surface CD32A, whereas CD32A(R)-Ig blocked only CD32A(R) and was unable to cross-block IC binding mediated by CD32A(H). Two-dimensional affinity measurements also demonstrated that CD32A(R) has significantly lower affinity toward all three subtypes as compared with CD32A(H). Our data suggest that the lower binding of CD32A(R) not only to IgG2 but also to IgG1 and IgG3 might be responsible for the lack of clearance of IC leading to increased susceptibility to bacterial infections and autoimmune diseases. Our data further suggests that in humans, inflammatory cells from CD32A(R/H) heterozygous individuals may predominantly use the H allele to mediate Ab-coated target cell binding during phagocytosis and Ab-dependent cellular cytotoxicity, resulting in a phenotype similar to CD32A(H) homozygous individuals.

Serum levels of autoantibodies against C-reactive protein correlate with renal disease activity and response to therapy in lupus nephritis

Introduction

Serum levels of C-reactive protein (CRP) seldom reflect disease activity in systemic lupus erythematosus (SLE). We have previously shown that autoantibodies against neo-epitopes of CRP often occur in SLE, but that this does not explain the modest CRP response seen in flares. However, we have repeatedly found that anti-CRP levels parallel lupus disease activity, with highest levels in patients with renal involvement; thus, we aimed to study anti-CRP in a material of well-characterized lupus nephritis patients.

Methods

Thirty-eight patients with lupus nephritis were included. Treatment with corticosteroids combined with cyclophosphamide, mycophenolate mofetil or rituximab was started after baseline kidney biopsy. A second biopsy was taken after ≥ 6 months. Serum creatinine, cystatin C, complement, anti-dsDNA, anti-CRP and urinalysis were done on both occasions. Biopsies were evaluated regarding World Health Organisation (WHO) class and indices of activity and chronicity. Renal disease activity was estimated using the British Isles Lupus Assessment Group (BILAG) index.

Results

At baseline, 34/38 patients had renal BILAG-A; 4/38 had BILAG-B. Baseline biopsies showed WHO class III (n = 8), IV (n = 19), III to IV/V (n = 3) or V (n = 8) nephritis. Seventeen out of 38 patients were anti-CRP-positive at baseline, and six at follow-up. Overall, anti-CRP levels had dropped at follow-up (P < 0.0001) and anti-CRP levels correlated with renal BILAG (r = 0.29, P = 0.012). A positive anti-CRP test at baseline was superior to anti-dsDNA and C1q in predicting poor response to therapy as judged by renal BILAG. Baseline anti-CRP levels correlated with renal biopsy activity (r = 0.33, P = 0.045), but not with chronicity index. Anti-CRP levels were positively correlated with anti-dsDNA (fluorescence-enhanced immunoassay: r = 0.63, P = 0.0003; Crithidia luciliae immunofluorescence microscopy test: r = 0.44, P < 0.0001), and inversely with C3 (r = 0.35, P = 0.007) and C4 (r = 0.29, P = 0.02), but not with C1q (r = 0.14, P = 0.24). No associations with urinary components, creatinine, cystatin C or the glomerular filtration rate were found.

Conclusions

In the present study, we demonstrate a statistically significant correlation between anti-CRP levels and histopathological activity in lupus nephritis, whereas a baseline positive anti-CRP test predicted poor response to therapy. Our data also confirm previous findings of associations between anti-CRP and disease activity. This indicates that anti-CRP could be helpful to assess disease activity and response to therapy in SLE nephritis, and highlights the hypothesis of a pathogenetic role for anti-CRP antibodies in lupus nephritis.

Functional and clinical consequences of Fc receptor polymorphic and copy number variants

Receptors for immunoglobulins (Fc receptors) play a central role during an immune response, as they mediate the specific recognition of antigens of almost infinite diversity by leucocytes, thereby linking the humoral and cellular components of immunity. Indeed, engagement of Fc receptors by immunoglobulins initiates a range of immunoregulatory processes that might also play a role in disease pathogenesis. In the circulation, five main types of immunoglobulins (Ig) exist - namely IgG, IgA, IgE, IgM and IgD and receptors with the ability to recognize and bind to IgG (Fc gamma receptor family), IgE (Fc epsilon RI and CD23), IgA (CD89; Fc alpha/microR) and IgM (Fc alpha/microR) have been identified and characterized. However, it is astonishing that nearly all the known human Fc receptors display extensive genetic variation with clear implications for their function, thus representing a substantial genetic risk factor for the pathogenesis of a range of chronic inflammatory disorders.

FcgammaRIIa genotype is associated with acute coronary syndromes as first manifestation of coronary artery disease

OBJECTIVE

Identification of clinically relevant determinants for acute coronary syndromes (ACS) promises reduction of ACS-associated mortality. C-reactive protein (CRP) has proved to be useful identifying people at risk for cardiovascular events. However, it is unknown whether genetic variants at Fcgamma receptor IIa (FcgammaRIIa), the main receptor for CRP, are involved in CRP-related cardiovascular risk. We evaluated the potential impact of FcgammaRIIa through a genetic association study in patients with ACS.

METHODS AND RESULTS

We conducted a genetic association study among 701 consecutive patients with first event of ACS compared to 467 patients with stable angina pectoris. All patients were genotyped for a frequent functional variant at position 131 of the mature FcgammaRIIa, where the arginine (R) allele results in an increased signal transduction upon CRP binding. In our study, the R/R131 genotype was significantly associated with ACS as the first manifestation of coronary artery disease (P=1.2x10(-9), odds ratio 2.86, 95% CI: 2.06-3.99) compared to the non-R/R131 genotype.

CONCLUSIONS

Our data show a genetic association of the FcgammaRIIa R/R131 genotype with a more frequent occurrence of ACS as the first manifestation of coronary artery disease, probably mediated via its interaction with CRP. Genotyping of this FcgammaRIIa variant could help to improve risk stratification in the course of coronary disease in the future.

Systemic lupus erythematosus in a multiethnic US cohort (LUMINA): LXI. Value of C-reactive protein as a marker of disease activity and damage

OBJECTIVE

To determine whether C-reactive protein (CRP) measured by a high sensitivity (hs) assay is a surrogate marker of disease activity and damage in systemic lupus erythematosus (SLE).

METHODS

Five hundred eighty-eight patients with SLE participating in a multiethnic cohort (Hispanic, African American, and Caucasian) were studied. Disease activity was measured with the Systemic Lupus Activity Measure-Revised (SLAM-R) and damage with the Systemic Lupus International Collaborating Clinics (SLICC) Damage Index (SDI). hs-CRP was measured by immunometric assay. Disease activity and hs-CRP were measured at enrollment and damage accrual at last visit. The association of hs-CRP with the SLAM-R and SDI was examined by univariable (Pearson's correlation) and multivariable (linear regression) analyses. The association of hs-CRP and each individual domain of the SLAM-R and SDI was examined by Spearman's correlation.

RESULTS

hs-CRP was associated with the SLAM-R in the univariable (r = 0.35, p < 0.001) and multivariable (t = 7.11, coefficient beta = 0.27, p < 0.001) analyses. It also correlated with the constitutional, eye, pulmonary, gastrointestinal, neuromotor, and laboratory domains of the SLAM-R. hs-CRP was associated with the SDI (r = 0.12, p = 0.004) in the univariable analysis but not in the multivariable analysis. When the individual domains of the SDI were analyzed, hs-CRP correlated with the renal, pulmonary, cardiovascular, musculoskeletal, and diabetes domains.

CONCLUSIONS

hs-CRP was associated with disease activity but not with overall damage accrual; however, it correlated with specific domains of the damage index. hs-CRP may be useful to monitor the course of the disease and predict its intermediate outcome, but longitudinal studies with serial hs-CRP measurements are necessary to define its clinical value.

Interethnic differences in carriage of haemoglobin AS and Fcgamma receptor IIa (CD32) genotypes in children living in eastern Sudan

Fulani and Masaleit, two sympatric ethnic groups in eastern Sudan, are characterized by marked differences in susceptibility to Plasmodium falciparum malaria. It has been suggested that sickle cell trait carriage may protect from the most severe forms of malaria. Previously, we have shown that FcgammaRIIa polymorphism is associated with the outcome of malaria disease. The present study aimed at determining whether the two tribes differ in the frequency of FcgammaRIIa and Hb AS genotypes. For this, genotyping of FcgammaRIIa and Hb AS in 70 Fulani and 70 Masaleit age- and sex-matched subjects was conducted. The frequency of FcgammaRIIa H/H131 genotype was higher in the Fulani as compared to the Masaleit group (40.0% versus 14.3%; adjusted odd ratio [OR]=3.05, 95% confidence interval [CI]=1.19-7.82 and P=0.02), while the R/R131 genotype was significantly higher in the Masaleit group (14.3% for Fulani versus 45.0% for Masaleit; adjusted OR=0.26, 95% CI=0.11-0.64 and P<0.01). With regard to FcgammaRIIa allele frequencies, there were significant differences between the Fulani and Masaleit ethnic groups. Thus, the H131 allele was more frequent than the R131 among Fulani children (0.63 versus 0.37, OR=3.23, 95% CI=1.93-5.45 and P<0.001). The frequency of the Hb AS genotype was lower in the Fulani compared to the Masaleit group (15.7% versus 30.0%, respectively, adjusted OR=0.02, CI=0.01-0.18 and P<0.01). These data suggest that FcgammaRIIa and Hb AS polymorphisms may contribute to the clinical outcome of malaria. We conclude that the H/H131 genotype and H131 allele rather than Hb AS genotype (sickle cell trait patients) appear to associate with the Fulani ethnic group.

High-sensitivity C-reactive protein as an associate of clinical subsets and organ damage in systemic lupus erythematosus

OBJECTIVE

C-reactive protein (CRP) may play an anti-inflammatory role during the acute phase of inflammation and is also used as a marker of inflammation associated with cardiovascular disease. In the present study, we investigated the association between high-sensitivity CRP (hsCRP) and systemic lupus erythematosus (SLE) manifestations, autoantibodies, and organ damage.

METHODS

In this cross-sectional study, 610 SLE patients from a prospective cohort had more than 1 hsCRP measurement. Organ damage was assessed using the Systemic Lupus International Collaborating Clinics (SLICC)/American College of Rheumatology Damage Index. Multiple linear regression models were used to adjust for age, gender, ethnicity, disease duration, body mass index, education, disease activity, current prednisone dose, statin use, and estrogen use.

RESULTS

After adjusting for confounders, hsCRP was associated with myocarditis, cardiac murmur, interstitial pulmonary fibrosis, pulmonary hypertension, gastrointestinal lupus manifestations, and anemia. Anti-dsDNA antibodies and lupus anticoagulant were associated with hsCRP in unadjusted models, and these associations remained significant after adjustment for confounders. hsCRP levels were significantly higher in patients with pulmonary, musculoskeletal, and endocrine damage, and a total SLICC Damage Index score>or=1. After adjustment, hsCRP was associated with pulmonary, musculoskeletal, and total damage, but no longer with endocrine damage.

CONCLUSIONS

hsCRP is associated with a broad range of clinical features and organ damage in SLE, particularly in the pulmonary and musculoskeletal systems. This association holds true independent of sociodemographic, disease activity, and treatment factors and may be useful to identify high-risk SLE patients who would benefit from additional screening and surveillance studies.

Pathogenic implications for autoantibodies against C-reactive protein and other acute phase proteins

Systemic lupus erythematosus (SLE) is a systemic rheumatic disease characterized clinically by multiorgan involvement and serologically by the occurrence of antinuclear antibodies. SLE patients may present with multiple autoantibodies to cytoplasmic and cell surface antigens as well as to circulating plasma proteins. Another feature of SLE is that serum levels of C-reactive protein (CRP) often remain low despite high disease activity and despite high levels of other acute phase proteins and interleukin-6, i.e. the main CRP inducing cytokine. Apart from its important role as a laboratory marker of inflammation, CRP attracts increasing interest due to its many intriguing biological functions, one of which is a role as an opsonin contributing to the elimination of apoptotic cell debris, e.g. nucleosomes, thereby preventing immunization against autoantigens. Recently, autoantibodies against CRP and other acute phase proteins have been reported in certain rheumatic conditions, including SLE. Although the presence of anti-CRP autoantibodies does not explain the failed CRP response in SLE, antibodies directed against acute phase proteins have several implications of pathogenetic interest. This paper thus highlights the biological and clinical aspects of native and monomeric CRP and anti-CRP, as well as autoantibodies against mannose-binding lectin, serum amyloid A and serum amyloid P component.

Antibodies against C-reactive protein cross-react with 60-kilodalton heat shock proteins

C-reactive protein (CRP) is an acute-phase reactant frequently used in histochemistry as a marker of ongoing inflammation. Furthermore, CRP is a powerful biomarker for the prediction of coronary artery disease risk. Heat-shock protein 60 (Hsp60) and CRP are complement-activating molecules, and the effect of their interactions on the regulation of complement activation was studied. However, during the first experiments, we learned that polyclonal anti-CRP antibodies cross-react with Hsp60. Therefore, the aim of our present study was to analyze the cross-reactivity of anti-CRP antibodies (Ab) with Hsp60 in solid-phase enzyme immune assays, in epitope studies using a series of overlapping synthetic peptides, and in Ouchterlony analyses. We found that three different commercial rabbit polyclonal antibodies and two monoclonal (9C9 and CRP-8) anti-CRP antibodies specifically recognize recombinant human Hsp60 and recombinant Mycobacterium tuberculosis Hsp65, respectively. Hsp60 was found to inhibit the binding of anti-CRP polyclonal Ab to Hsp60. Six epitope regions of Hsp60 were recognized by the anti-CRP antibodies, and one region (amino acids [AA] 218 to 232) was recognized by monoclonal antibodies CRP-8 and 9C9. This epitope region of Hsp60 displays 26.6% amino acid identity to CRP AA region 77 to 90. These data suggest that the B-cell epitopes shared between CRP and Hsp60 give rise to a true mimicry-based cross-reaction and the induction of cross-reactive antibodies. Our study underlines the importance of thorough study design and careful interpretation of results while using polyclonal anti-CRP antibodies for histochemistry, especially at low dilutions. Furthermore, analytical interference with Hsp60 in CRP assays should also be tested.

C-reactive protein induces NF-kappaB activation through intracellular calcium and ROS in human mesangial cells

BACKGROUND

C-reactive protein (CRP) is known to have a direct proinflammatory effect in endothelial cells. However, little is known about the effect of CRP in intrinsic renal cells. We investigated the effects of CRP on the nuclear factor-kappaB (NF-kappaB) activation and monocyte chemoattractant protein-1 (MCP-1) gene expression in human mesangial cells and also examined whether intracellular calcium and reactive oxygen species (ROS) were involved in the CRP- induced NF-kappaB activation.

METHODS

NF-kappaB binding activity and MCP-1 mRNA expression were measured by electrophoretic mobility shift assay and Northern blot analysis, respectively. Intracellular calcium was monitored by confocal microscopy using calcium sensitive dye, Fluo-3 and intracellular ROS production was determined, using 2',7'-dichlorofluorescin diacetate.

RESULTS

CRP increased NF-kappaB binding activity in a dose-dependent manner (12.5-100 microg/ml), which was induced within 1 h after incubation and peaked around 3 h. CRP also increased the MCP-1 mRNA expression via activation of NF-kappaB. Both intracellular calcium and ROS was induced by CRP. Calcium chelator, BAPTA-AM and anti-oxidants such as N-acetylcysteine and tiron suppressed CRP-induced NF-kappaB activation.

CONCLUSION

CRP exerted a proinflammatory effect in human mesangial cells by inducing MCP-1 gene expression via NF-kappaB activation, which was mediated, at least in part, through intracellular calcium and ROS.

Prognostic factors in lupus nephritis

Systemic lupus erythematosus (SLE) is a heterogeneous disorder and its renal manifestations are protean. The course and prognosis of lupus nephritis is dependent on a large number of demographic, histopathological, serological, racial, socioeconomic and time dependent factors. Moreover, the initial and maintenance therapeutic regimens may also influence the long term renal outcome. This article reviews the important prognostic factors that have been reported in literature. The management strategy of lupus nephritis should be individualized and based on a composite of these parameters.

Human Factor H-Related Protein 5 Has Cofactor Activity, Inhibits C3 Convertase Activity, Binds Heparin and C-Reactive Protein, and Associates with Lipoprotein

Factor H-related protein 5 (FHR-5) is a recently discovered member of the factor H (fH)-related protein family. FHR proteins are structurally similar to the complement regulator fH, but their biological functions remain poorly defined. FHR-5 is synthesized in the liver and consists of 9 short consensus repeats (SCRs), which display various degrees of homology to those of fH and the other FHR proteins. FHR-5 colocalizes with complement deposits in vivo and binds C3b in vitro, suggesting a role in complement regulation or localization. The current study examined whether rFHR-5 exhibits properties similar to those of fH, including heparin binding, CRP binding, cofactor activity for the factor I-mediated degradation of C3b and decay acceleration of the C3 convertase. rFHR-5 bound heparin-BSA and heparin-agarose and a defined series of truncations expressed in Pichia pastoris localized the heparin-binding region to within SCRs 5-7. rFHR-5 bound CRP, and this binding was also localized to SCRs 5-7. FHR-5 inhibited alternative pathway C3 convertase activity in a fluid phase assay; however, dissociation of the convertase was not observed in a solid phase assay. rFHR-5 displayed factor I-dependent cofactor activity for C3b cleavage, although it was apparently less effective than fH. In addition, we demonstrate association of FHR-5 with high density lipid lipoprotein complexes in human plasma. These results demonstrate that FHR-5 shares properties of heparin and CRP binding and lipoprotein association with one or more of the other FHRs but is unique among this family of proteins in possessing independent complement-regulatory activity.

C-reactive protein: an activator of innate immunity and a modulator of adaptive immunity

C-reactive protein (CRP) is an acute-phase serum protein and a member of the pentraxin protein family. Its host defense functions predate the adaptive immune system by millions of years. Our current understanding of CRP interactions with complement and with Fcgamma receptors (FcgammaR) have led to an increased appreciation of the regulatory role of CRP in inflammation and autoimmunity. This review outlines the role of CRP in infection, inflammation, and autoimmune disease. We provide a description of recent studies, which suggest that CRP acts through FcgammaR to reduce inflammation and protect from certain autoimmune diseases. A general description of the proposed function of CRP is provided as a framework for future investigation.