Autoantibodies to C-reactive protein (CRP) and other acute-phase proteins in systemic autoimmune diseases

The Role of Anti-mCRP Autoantibodies in Lupus Nephritis

Background

Lupus nephritis is characterized by multiple autoantibodies production. However, there are few autoantibodies associated with disease activity and prognosis. CRP exists in at least two conformationally distinct forms: native pentameric C-reactive protein (pCRP) and modified/monomeric CRP (mCRP). Autoantibodies against mCRP are prevalent in sera of patients with lupus nephritis and are reported to be pathogenic.

Summary

The levels of serum anti-mCRP autoantibodies are associated with clinical disease activity, tubulointerstitial lesions, treatment response, and prognosis in patients with lupus nephritis. The key epitope of mCRP was amino acid 35-47. Furthermore, emerging evidence indicated that anti-mCRP autoantibodies could participate in the pathogenesis of lupus nephritis by forming in situ immune complexes or interfering with the biological functions of mCRP, such as binding to complement C1q and factor H.

Key Messages

Here, we review the recent advances in the prevalence, clinical-pathological associations, and potential pathogenesis of anti-mCRP autoantibodies in lupus nephritis, which may provide a promising novel therapeutic strategy for lupus nephritis.

C-Reactive Protein: Pathophysiology, Diagnosis, False Test Results and a Novel Diagnostic Algorithm for Clinicians

The current literature provides a body of evidence on C-Reactive Protein (CRP) and its potential role in inflammation. However, most pieces of evidence are sparse and controversial. This critical state-of-the-art monography provides all the crucial data on the potential biochemical properties of the protein, along with further evidence on its potential pathobiology, both for its pentameric and monomeric forms, including information for its ligands as well as the possible function of autoantibodies against the protein. Furthermore, the current evidence on its potential utility as a biomarker of various diseases is presented, of all cardiovascular, respiratory, hepatobiliary, gastrointestinal, pancreatic, renal, gynecological, andrological, dental, oral, otorhinolaryngological, ophthalmological, dermatological, musculoskeletal, neurological, mental, splenic, thyroid conditions, as well as infections, autoimmune-supposed conditions and neoplasms, including other possible factors that have been linked with elevated concentrations of that protein. Moreover, data on molecular diagnostics on CRP are discussed, and possible etiologies of false test results are highlighted. Additionally, this review evaluates all current pieces of evidence on CRP and systemic inflammation, and highlights future goals. Finally, a novel diagnostic algorithm to carefully assess the CRP level for a precise diagnosis of a medical condition is illustrated.

Association of C-reactive protein and complement factor H gene polymorphisms with risk of lupus nephritis in Chinese population

BACKGROUND

Complement overactivation is a major driver of lupus nephritis (LN). Impaired interactions of C-reactive protein (CRP) with complement factor H (CFH) have been shown as a pathogenic mechanism that contributes to the overactivation of complement in LN. However, genetic variations of neither CRP nor CFH show consistent influences on the risk of LN.

AIM

To examine whether genetic variations of CRP and CFH in combination can improve the risk stratification in Chinese population.

METHODS

We genotyped six CRP single nucleotide polymorphisms (SNPs) (rs1205, rs3093062, rs2794521, rs1800947, rs3093077, and rs1130864) and three CFH SNPs (rs482934, rs1061170, and rs1061147) in 270 LN patients and 303 healthy subjects.

RESULTS

No linkage was found among CRP and CFH SNPs, indicating lack of genetic interactions between the two genes. Moreover, CRP and CFH SNPs, neither individually nor in combination, are associated with the risk or clinical manifestations of LN. Given the unambiguous pathogenic roles of the two genes.

CONCLUSION

These findings suggest that the biological effects of most genetic variations of CRP and CFH on their expressions or activities are not sufficient to influence the disease course of LN.

Presence of coronary aneurysms during Kawasaki Disease (KD) correlates with lower levels of autoantibodies to both full form and spliced variant of immune regulator Del-1

Kawasaki disease (KD), a rare multisystem inflammatory condition that predominantly affects children under six years of age, is the leading cause of childhood-acquired heart disease in developed countries. The pathogenesis is unknown, but studies support that an infectious stimulus triggers an autoimmune reaction in a genetically susceptible child. Recent studies demonstrated an association with autoantibody response to Del-1 (also known as EDIL3) in children with KD. Del-1 is an extracellular matrix protein that is expressed both in macrophages and vascular endothelium. Del-1 has an anti-inflammatory role by preventing leucocyte migration to inflammatory sites. Del-1 has two expression variants and genetic variants of Del-1 have been associated with the risk of intracranial aneurysms. Due to the physiologic plausibility for a role during KD, we chose to assess if autoantibodies against DEL-1 are seen in a larger cohort of children with KD and to assess if responses correlated to aneurysm formation. Contrary to prior findings, in comparison to febrile controls, autoantibodies were not overall higher in children with KD. Elevation in Post-IVIG samples in comparison to pre-IVIG and convalescent samples supports the commonality of anti-Del-1 antibodies. Autoantibodies were notably lower in children with KD who had coronary Z score elevations in comparison to those who did not.

Systemic Activation of the Kynurenine Pathway in Graves` Disease with and without Ophthalmopathy

PURPOSE

To characterize the kynurenine pathway, activated during interferon-γ mediated inflammation and cellular (Th1-type) immunity, in Graves` disease (GD) patients with and without thyroid eye disease (TED).

METHODS

We analyzed 34 biomarkers by mass spectrometry in serum samples from 100 patients with GD (36 with TED) and 100 matched healthy controls. The analytes included 10 metabolites and three indices from the kynurenine pathway, six microbiota-derived metabolites, 10 B-vitamers and five serum proteins reflecting inflammation and kidney function.

RESULTS

GD patients showed significantly elevated levels of seven biomarkers compared with healthy controls (omega squared (ω2) > 0.06, P < 0.01). Out of these seven, the six biomarkers with the strongest effect size were all components of the kynurenine pathway. Factor analysis showed that biomarkers related to cellular immunity and the Th1 responses (3-hydroxykynurenine, kynurenine and quinolinic acid with the highest loading) were most strongly associated with GD. Further, a factor mainly reflecting acute phase response (CRP and serum amyloid A) showed weaker association with GD by factor analysis. There were no differences in biomarker levels between GD patients with and without TED.

CONCLUSION

This study supports activation of interferon-γ inflammation and Th1 cellular immunity in GD, but also a contribution of acute phase reactants. Our finding of no difference in systemic activation of the kynurenine pathway in GD patients with and without TED implies that the local Th1 immune response in the orbit is not reflected systemically.

The Complex Role of C-Reactive Protein in Systemic Lupus Erythematosus

C-reactive protein (CRP) is well-known as a sensitive albeit unspecific biomarker of inflammation. In most rheumatic conditions, the level of this evolutionarily highly conserved pattern recognition molecule conveys reliable information regarding the degree of ongoing inflammation, driven mainly by interleukin-6. However, the underlying causes of increased CRP levels are numerous, including both infections and malignancies. In addition, low to moderate increases in CRP predict subsequent cardiovascular events, often occurring years later, in patients with angina and in healthy individuals. However, autoimmune diseases characterized by the Type I interferon gene signature (e.g., systemic lupus erythematosus, primary Sjögren’s syndrome and inflammatory myopathies) represent exceptions to the general rule that the concentrations of CRP correlate with the extent and severity of inflammation. In fact, adequate levels of CRP can be beneficial in autoimmune conditions, in that they contribute to efficient clearance of cell remnants and immune complexes through complement activation/modulation, opsonization and phagocytosis. Furthermore, emerging data indicate that CRP constitutes an autoantigen in systemic lupus erythematosus. At the same time, the increased risks of cardiovascular and cerebrovascular diseases in patients diagnosed with systemic lupus erythematosus and rheumatoid arthritis are well-established, with significant impacts on quality of life, accrual of organ damage, and premature mortality. This review describes CRP-mediated biological effects and the regulation of CRP release in relation to aspects of cardiovascular disease and mechanisms of autoimmunity, with particular focus on systemic lupus erythematosus.

A Review of Anti-C Reactive Protein Antibodies in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE), the prototype autoimmune disease, is characterized by the production of a plethora of autoantibodies with various roles in the development of disease-related tissue damage. C-reactive protein (CRP) is an acute phase reactant with a pentameric structure. Under acidic or alkaline conditions, or when urea levels are high and/or calcium levels are low, the pentamer (pCRP) dissociates irreversibly into monomeric CRP (mCRP) and exposes new epitopes (neo-CRP). Importantly, anti-mCRP (but not anti-pCRP) antibodies have been described in patients with SLE, their prevalence varying from 4% to 78% in different cohorts. Numerous studies have investigated the relationship between autoantibodies directed against CRP (anti-CRP) and disease activity as well as their association with lupus nephritis (LN), frequently reporting discrepant findings. The main objective of the present review is to describe the role of anti-mCRP antibodies in SLE according to the currently available data.

Anti-Pentraxin Antibodies in Autoimmune Diseases: Bystanders or Pathophysiological Actors?

Pentraxins are soluble innate immunity receptors involved in sensing danger molecules. They are classified as short (CRP, SAP) and long pentraxin subfamilies, including the prototypic long pentraxin PTX3. Pentraxins act mainly as bridging molecules favoring the clearance of microbes and dead cells. They are also involved in many other biological processes, such as regulation of complement activation, inflammation and tissue homeostasis. Autoantibodies directed against pentraxins have been reported in various autoimmune diseases, especially in systemic lupus erythematosus and ANCA-associated vasculitis. In this review, we review the main biological characteristics and functions of pentraxins and summarize data concerning autoantibodies directed against pentraxins in the context of autoimmune diseases and discuss their potential pathological role.

Cutaneous lupus erythematosus: factors related to cutaneous activity and damage in a cohort of 260 patients from A Coruña, Spain

Background

Cutaneous lupus erythematosus is a chronic autoimmune disease that can leave important sequelae.

Objective

To determine the factors that predict the activity and damage of the skin disease, and the impact of tobacco on the efficacy of antimalarials using the Cutaneous Lupus Erythematosus Disease Area and Severity Index.

Materials and Methods

A consecutive case series was performed on 260 patients with cutaneous lupus erythematosus (α = 0.05; precision ± 6.5%). We carried out a descriptive analysis of the variables included, with a multivariate analysis to measure the association of variables with the Cutaneous Lupus Erythematosus Disease Area and Severity Index activity and damage ( p value < 0.05).

Results

The Cutaneous Lupus Erythematosus Disease Area and Severity Index activity was greater in smokers than non-smokers (4.0 ±5.3 vs 1.2 ±3.4, p = 0.006). No significant differences were observed in the Cutaneous Lupus Erythematosus Disease Area and Severity Index activity when the efficacy of antimalarials was analyzed between smokers and non-smokers. Cutaneous Lupus Erythematosus Disease Area and Severity Index damage was higher in smokers than in non-smokers (2.0 ± 3.6 vs 1.2 ± 2.6, p = 0.029). Cutaneous Lupus Erythematosus Disease Area and Severity Index activity was associated with: (a) being an active smoker (odds ratio 3.04, 95% confidence interval 1.68–5.51, p < 0.001; regression coefficient 2.05, 95% confidence interval 0.69–3.42, p = 0.003); (b) the chronic cutaneous lupus erythematosus subtype (odds ratio 1.98, 95% confidence interval 1.02–3.84, p = 0.044); and (c) C-reactive protein increase (≥0.5 mg/dL) (regression coefficient 2.56, 95% confidence interval 0.40–4.71, p = 0.020). Cutaneous Lupus Erythematosus Disease Area and Severity Index damage was associated with: (a) the activity (regression coefficient 0.11, 95% confidence interval 0.01–0.20, p = 0.024); (b) the chronic cutaneous lupus erythematosus subtype (regression coefficient 2.46, 95% confidence interval 1.37–3.56, p < 0.001); (c) the use of topical treatment (regression coefficient 1.31, 95% confidence interval 0.01–2.61, p = 0.049); and (d) systemic treatment (regression coefficient 1.44, 95% confidence interval 0.35–2.53, p < 0.010).

Conclusion

Smoking is related to an increase risk and a greater activity of cutaneous lupus erythematosus. The chronic cutaneous lupus erythematosus subtype and an increased C-reactive protein level were also associated with a higher disease activity. The sequelae were related to the activity, the chronic cutaneous lupus erythematosus subtype, and the use of topical and systemic treatment. The impact of tobacco on the efficacy of antimalarials may be caused by an increase in the severity of the disease more than by resistance in smokers.

The Multiple Faces of C-Reactive Protein-Physiological and Pathophysiological Implications in Cardiovascular Disease

C-reactive protein (CRP) is an intriguing protein which plays a variety of roles in either physiological or pathophysiological states. For years it has been regarded merely as a useful biomarker of infection, tissue injury and inflammation, and it was only in the early 80s that the modified isoforms (mCRP) of native CRP (nCRP) appeared. It soon became clear that the roles of native CRP should be clearly discriminated from those of the modified form and so the impacts of both isoforms were divided to a certain degree between physiological and pathophysiological states. For decades, CRP has been regarded only as a hallmark of inflammation; however, it has since been recognised as a significant predictor of future episodes of cardiovascular disease, independent of other risk factors. The existence of modified CRP isoforms and their possible relevance to various pathophysiological conditions, suggested over thirty years ago, has prompted the search for structural and functional dissimilarities between the pentameric nCRP and monomeric mCRP isoforms. New attempts to identify the possible relevance between the diversity of structures and their opposing functions have initiated a new era of research on C-reactive protein. This review discusses the biochemical aspects of CRP physiology, emphasizing the supposed relevance between the structural biology of CRP isoforms and their differentiated physiological and pathophysiological roles.

Determination of CRP Autoantibodies by SPR Immunoassay

Biosensors based on the principle of surface plasmon resonance (SPR) are surface-sensitive optical devices used for monitoring biomolecular interactions at the sensor surface in real time without any labeling. It is used in a wide variety of areas including proteomics, clinical diagnosis, environmental monitoring, drug discovery, and food analysis. C-reactive protein (CRP) is a marker of inflammation, which undergoes conformation changes in local lesions, leading to the formation of mCRP. Autoantibodies against mCRP are frequently detected in systemic lupus erythematosus (SLE) and associated with disease activity and prognosis. An SPR immunoassay for CRP autoantibodies at complement factor H-CRP interface is described in this chapter.

High Prevalence of Autoantibodies Against Monomeric C Reactive Protein (CRP) in Children with PFAPA Syndrome

PFAPA (periodic fever, aphthous stomatitis, pharyngitis, cervical adenitis) syndrome is an autoinflammatory disorder of unknown etiology. The aim of our study was to evaluate whether the presence of anti-mCRP autoantibodies (anti-mCRP) might possibly contribute to systemic inflammation during PFAPA flares. We carried out anti-mCRP testing (in-house ELISA) in a single-center, prospective cohort of 30 PFAPA patients (12 girls). We found a high prevalence (43.3%) of anti-mCRP antibodies in PFAPA patients during their febrile episodes, which implies the possible involvement of anti-mCRP antibodies in PFAPA pathogenesis.

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.

Distinguishing infections vs flares in patients with systemic lupus erythematosus

SLE is a chronic autoimmune disease involving multiple systems. Patients with SLE are highly susceptible to infections due to the combined effects of their immunosuppressive therapy and the abnormalities of the immune system that the disease itself causes, which can increase mortality in these patients. The differentiation of SLE activity and infection in a febrile patient with SLE is extremely difficult. Activity indexes are useful to identify patients with lupus flares but some clinical and biological abnormalities may, however, make it difficult to differentiate flares from infection. Several biological markers are now recognized as potential tools to establish the difference between SLE activity and infection, including CRP and procalcitonin. It is possible, however, that the use of only one biomarker is not sufficient to confirm or discard infection. This means that new scores, which include different biomarkers, might represent a better solution for differentiating these two clinical pictures. This review article describes several markers that are currently used, or have the potential, to differentiate infection from SLE flares.

Autoantibodies against C-Reactive Protein Influence Complement Activation and Clinical Course in Lupus Nephritis

Autoantibodies against the major acute-phase reactant C-reactive protein (CRP) are frequently found in patients with lupus nephritis. Further defining the autoimmune epitopes on CRP may not only improve patient stratification but also, hint at mechanisms of CRP action. Herein, we show that amino acids 35-47 constitute the major epitope recognized by anti-CRP autoantibodies in patients with lupus nephritis. Notably, the presence of autoantibodies against amino acids 35-47 associated with more severe renal damage and predicted worse outcome. This epitope is exposed on CRP only after irreversible structure changes, yielding a conformationally altered form termed modified or monomeric CRP (mCRP). ELISA and surface plasmon resonance assays showed that amino acids 35-47 mediate the interaction of mCRP with complement factor H, an inhibitor of alternative pathway activation, and this interaction greatly enhanced the in vitro cofactor activity of complement factor H. In contrast, autoantibodies against amino acids 35-47 inhibited these actions of mCRP. Our results thus provide evidence for the in vivo generation of mCRP in a human disease and suggest that mCRP actively controls the pathogenesis of lupus nephritis by regulating complement activation. Therefore, amino acids 35-47 constitute a functional autoimmune epitope on CRP that can be targeted therapeutically and diagnostically.

Cell death in the pathogenesis of systemic lupus erythematosus and lupus nephritis

Nephritis is one of the most severe complications of systemic lupus erythematosus (SLE). One key characteristic of lupus nephritis (LN) is the deposition of immune complexes containing nucleic acids and/or proteins binding to nucleic acids and autoantibodies recognizing these molecules. A variety of cell death processes are implicated in the generation and externalization of modified nuclear autoantigens and in the development of LN. Among these processes, apoptosis, primary and secondary necrosis, NETosis, necroptosis, pyroptosis, and autophagy have been proposed to play roles in tissue damage and immune dysregulation. Cell death occurs in healthy individuals during conditions of homeostasis yet autoimmunity does not develop, at least in part, because of rapid clearance of dying cells. In SLE, accelerated cell death combined with a clearance deficiency may lead to the accumulation and externalization of nuclear autoantigens and to autoantibody production. In addition, specific types of cell death may modify autoantigens and alter their immunogenicity. These modified molecules may then become novel targets of the immune system and promote autoimmune responses in predisposed hosts. In this review, we examine various cell death pathways and discuss how enhanced cell death, impaired clearance, and post-translational modifications of proteins could contribute to the development of lupus nephritis.

Is there still a place for erythrocyte sedimentation rate and C-reactive protein in systemic lupus erythematosus?

The inflammatory response during systemic lupus erythematosus (SLE) flares is known to be atypical, characterized by a disproportionately lower C-reactive protein (CRP) elevation when compared with erythrocyte sedimentation rate (ESR). Thus, in these patients, the analysis of inflammatory markers might be challenging in daily clinical practice. Clinicians need frequently to distinguish lupus reactivations and infectious conditions, and the significance of ESR and CRP seems to be different. Even though a non-specific marker of inflammation, ESR utility in SLE should not be neglected and it appears to be a useful biomarker for SLE activity assessment. Describing a specific cut-off for ESR in SLE is important for patients' follow-up, and levels up to 25-30 mm/h have been proposed as an upper limit of the normal range. Regarding CRP, even though higher baseline levels are described in SLE when compared with controls, including in remission periods, its response during flares seems to be incomplete and not always correlated with disease activity; while CRP values greater than 10 mg/l could be indicative for severe flares, when there is no serositis or arthritis, higher CRP levels above 50-60 mg/l may be associated with infection.

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.

Pathogenic role of antibodies against monomeric C-reactive protein in tubulointerstitial nephritis and uveitis syndrome

Antibodies against monomeric C-reactive protein, which is a target antigen expressed both in kidney tubules and uveal cells, have been recently detected in patients with active tubulointerstitial nephritis and uveitis syndrome. We report the case of an 65-year-old woman with acute renal failure caused by biopsy-proven tubulointerstitial nephritis and the onset of uveitis 21 months later. The expression of monomeric C-reactive protein in kidney oligobiopsy was confirmed by immunohistochemical staining using mouse monoclonal antibody against human monomeric C-reactive protein. The levels of antibodies against monomeric C-reactive protein were 117% of the reference during the flare and 22% during the remission of the disease. The difference in the levels of antibodies against monomeric C-reactive protein during flare and remission, and above all positive biopsy staining, supports their pathogenic role in this disease.

Autoantibodies against C-reactive protein (CRP) in sera of patients with systemic rheumatic diseases

Abstract An assessment of the frequency of serum autoantibodies against modified C-reactive protein (mCRP) in systemic rheumatic diseases and the association of these autoantibodies with clinical and laboratory findings in patients with systemic lupus erythematosus (SLE). Serum levels of autoantibodies against mCRP were measured by an enzyme-linked immunosorbent assay in 125 patients with SLE and in 213 patients with other systemic rheumatic diseases. The frequency of patients with high antimodified CRP antibody levels was 32% in SLE, 22% in systemic sclerosis (SSc), 19% in polymyositis/dermatomyositis (PM/DM), 43% in primary Sjögren's syndrome (pSS), 29% in rheumatoid arthritis (RA), 33% in mixed connective tissue disease (MCTD), and 43% in overlap syndrome. Serum levels of anti-mCRP antibody were significantly lower in SLE patients with persistent proteinuria (P < 0.001), cellular casts (P < 0.01), and hypoalbuminemia (P < 0.05). Serum anti-mCRP antibody levels in SLE showed a direct correlation with serum IgG levels (P < 0.001), serum anti-SS-A antibody levels (P < 0.01), serum anti-SS-B antibody levels (P < 0.01), and serum anti-U1-RNP antibody levels (P < 0.05). Inhibition experiments revealed that nonnative epitopes on the CRP molecule, termed mCRP, were the main target of the anti-mCRP antibodies detected. Autoantibodies against mCRP were frequently found in sera from patients with systemic rheumatic diseases, and may have a role in the immunopathogenesis of systemic rheumatic diseases, which are characterized by persistent inflammation.

Sialic acid level reflects the disturbances of glycosylation and acute-phase reaction in rheumatic diseases

In the rheumatic diseases, the changes in the carbohydrate part of serum glycoproteins occur and these abnormalities can be monitored by serum level of total and free sialic acid. The aim of this study was to evaluate the total and free sialic acid level as a marker of inflammation activity (TSA) and the changes in glycosylation of blood glycoproteins (FSA) in rheumatoid arthritis (RA), systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). Studies were carried out in 50 patients with RA, 24 with SLE and 32 with SSc. TSA concentration was measured with an enzymatic, colorimetric method and FSA with a thiobarbituric method. The serum levels of TSA in RA and SLE patients were significantly increased compared to controls and in RA patients were higher than that in SSc patients. The mean serum level of FSA in RA patients was significantly higher, but in SSc patients significantly lower than that in the controls, and in RA patients was significantly higher than in SLE and in SSc patients. All acute-phase proteins were changed: Positive acute-phase proteins were elevated, and the negative protein was decreased. The positive acute-phase proteins positively correlated with the levels of TSA and FSA in RA and SSc patients. In SLE patients, TSA positively correlated with haptoglobin and α1-antitrypsin. In RA patients, there was the positive correlation of TSA and FSA with DAS 28. The changes in the serum levels of TSA and FSA in the course of rheumatic diseases could reflect the abnormalities in glycosylation/sialylation patterns of glycoproteins induced by acute-phase response.

Anti-C reactive protein antibodies in Indian patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by over production of autoantibodies. C-reactive protein (CRP) is a phylogenetically highly conserved plasma protein that participates in the systemic response to inflammation. Anti-CRP antibodies might have biological functions of pathogenetic interest in SLE. We evaluated anti-CRP antibodies in Indian SLE patients and their association with anti-dsDNA antibodies and complement levels (C3 and C4). One hundred SLE patients diagnosed according to the American College of Rheumatology criteria were included. Disease activity was assessed using SLE disease activity index (SLEDAI). Anti-CRP autoantibodies were detected by enzyme linked immunosorbent assay. Anti-dsDNA antibodies were detected by indirect immunofluroscence test (Euroimmun Lubeck, Germany). High sensitivity CRP and complement levels (C3, C4) were detected using a Nephelometer. (BN ProSpec, Dade Behring, Germany). Anti-CRP antibodies were detected in 26% of SLE patients. Mean age of disease onset among anti-CRP positives was 22.4 ± 7.5, and 26.6 ± 9.3 years among anti-CRP negatives (P > 0.05). Anti-dsDNA positivity was significantly higher among anti-CRP positives (32.7%) as compared to anti-CRP negatives (16%) (P = 0.00519). No statistically significant difference was observed in SLEDAI scores of anti-CRP positive group and anti-CRP negative group (P > 0.05). We observed a positive correlation between anti-CRP antibodies and anti-dsDNA antibodies.

Identification of an age-dependent biomarker signature in children and adolescents with autism spectrum disorders

Background

Autism spectrum disorders (ASDs) are neurodevelopmental conditions with symptoms manifesting before the age of 3, generally persisting throughout life and affecting social development and communication. Here, we have investigated changes in protein biomarkers in blood during childhood and adolescent development.

Methods

We carried out a multiplex immunoassay profiling analysis of serum samples from 37 individuals with a diagnosis of ASD and their matched, non-affected siblings, aged between 4 and 18 years, to identify molecular pathways affected over the course of ASDs.

Results

This analysis revealed age-dependent differences in the levels of 12 proteins involved in inflammation, growth and hormonal signaling.

Conclusions

These deviations in age-related molecular trajectories provide further insight into the progression and pathophysiology of the disorder and, if replicated, may contribute to better classification of ASD individuals, as well as to improved treatment and prognosis. The results also underline the importance of stratifying and analyzing samples by age, especially in ASD and potentially other developmental disorders.

CRP/anti-CRP antibodies assembly on the surfaces of cell remnants switches their phagocytic clearance toward inflammation

Systemic lupus erythematosus (SLE) is a chronic inflammatory disease characterized by the production of autoantibodies, formation of immune complexes (IC), and activation of complement that ultimately fuel acute and/or chronic inflammation. Accumulation in blood and tissues of post-apoptotic remnants is considered of etiological and pathological importance for patients with SLE. Besides receptors directly recognizing apoptotic cells, soluble opsonins of the innate immune system bind apoptotic material dependent on the stage of apoptosis. We describe the binding to the surface of secondary necrotic cells (SNEC) of the serum opsonin CRP and further opsonins. We show that anti-dsDNA and anti-CRP autoantibodies bind and sensitize SNEC. Autoantibody-sensitized SNEC were cleared by macrophages in vitro and induced a pro-inflammatory cytokine response. In conclusion, anti-CRP, CRP, and SNEC form a ternary pyrogen endowed with strong pro-inflammatory capabilities which is able to maintain and perpetuate chronic inflammation.

Periodontal disease as a risk factor for cardiovascular disease: suggestion of a further link in systemic lupus erythematosus

Cardiovascular disease (CVD) is a major cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Due to either infection or disease activity, elevated levels of inflammatory markers and up-regulation of the autoimmune process can contribute to the development of atherosclerosis in SLE patients. Periodontal diseases are among the most prevalent chronic infections in humans and are characterized by pathogen-induced oral inflammatory disease affecting the supporting tissues of teeth. Several cytokines capable of inducing systemic effects are produced during the course of this infection. The presence of these cytokines can be verified by changes in the levels of C-reactive protein (CRP). Periodontal disease is a well-known risk factor for atherosclerosis. The potential for beneficial prevention of CVD events through the use of periodontal treatment has been previously recommended. This review reinforces the hypothesis that periodontal infection could be a risk factor for CVD in patients diagnosed with SLE, and suggests that by reducing the progression of this oral infection, levels of inflammatory markers common to both diseases (SLE and periodontal disease) would likely decrease.

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.

Inefficient clearance of dying cells in patients with SLE: anti-dsDNA autoantibodies, MFG-E8, HMGB-1 and other players

Systemic lupus erythematosus (SLE) is a complex disease resulting from inflammatory responses of the immune system against several autoantigens. Inflammation is conditioned by the continuous presence of autoantibodies and leaked autoantigens, e.g. from not properly cleared dying and dead cells. Various soluble molecules and biophysical properties of the surface of apoptotic cells play significant roles in the appropriate recognition and further processing of dying and dead cells. We exemplarily discuss how Milk fat globule epidermal growth factor 8 (MFG-E8), biophysical membrane alterations, High mobility group box 1 (HMGB1), C-reactive protein (CRP), and anti-nuclear autoantibodies may contribute to the etiopathogenesis of the disease. Up to date knowledge about these key elements may provide new insights that lead to the development of new treatment strategies of the disease.

Immunotoxic response of oleic acid anilide and its hydrolysis products in female MRL (+/+) mice

An epidemic of a multi-systemic disease, known as the toxic oil syndrome (TOS), was caused by consumption of edible oil denatured with 2% aniline. Oleic acid anilide (OAA) has been suggested as one of the most likely etiologic agents responsible for TOS based upon its presence in high quantities in TOS-related oil samples. The aim of this study was to evaluate the immune response of OAA and contribution of its hydrolysis products (aniline and oleic acid) in the immunotoxic response. Female MRL(+/+) mice were treated with equimolar doses of OAA, aniline or oleic acid (0.8 mmol/kg), i.p., twice a week for 6 weeks. The levels of immunoglobulins IgE, IgG and its isotypes (IgG(1), IgG(2a), IgG(2 b), and IgG(3)), and the appearance of antinuclear antibodies (ANA) were determined in the serum. Exposure to OAA and oleic acid caused significant increases in IgG, IgG(1), IgG(2a), and IgG(2b) levels as compared to aniline and control groups, whereas IgG(3) value increased only in OAA-treated mice. The IgE levels in OAA-, aniline-, and oleic acid-treated groups were higher than the controls. Among the various treatment groups, sera from 50% of the OAA-treated mice gave rise to intense homogenous fluorescence patterns on Hep-2 cells, suggesting the presence of significant levels of antinuclear antibodies (ANA). Furthermore, analysis of serum cytokines showed significant increases in G-CSF levels in OAA- and aniline-treated mice. Among the tissues examined, morphological changes were confined to the spleen, which showed increased lymphocyte population in OAA- and aniline-treated mice. These studies indicate that OAA and its hydrolysis products cause perturbations in the immune response, and could contribute to TOS-related immune derangements.

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.

Autoantibodies to Tumor Necrosis Factor in Patients with Rheumatoid Arthritis and Systemic Lupus Erythematosus

Objective.

To detect autoantibodies to tumor necrosis factor (TNF) in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), and to determine their clinical correlates.

Methods.

Ninety-two patients with RA and 62 with SLE were studied. Sera were examined for autoantibodies to TNF by enzyme linked immunoassay. Levels of these autoantibodies were analyzed in respect to markers of inflammation such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and joint erosions, as well as other clinical, laboratory, and therapeutic aspects of RA and SLE.

Results.

Anti-TNF levels were higher in those RA patients without erosions, but did not correlate with ESR or CRP.

Conclusion.

These observations suggest that autoantibody anti-TNF may be part of the innate immune system and may contribute to decreased inflammation in patients with RA.

The protective function of human C-reactive protein in mouse models of Streptococcus pneumoniae infection

Human C-reactive protein (CRP), injected intravenously into mice or produced inside mice by a human transgene, protects mice from death following administration of lethal numbers of Streptococcus pneumoniae. The protective effect of CRP is due to reduction in the concentration of bacteria in the blood. The exact mechanism of CRP-dependent killing of pneumococci and the partners of CRP in this process are yet to be defined. The current efforts to determine the mechanism of action of CRP in mice are directed by four known in vitro functions of CRP: 1. the ability of pneumococcal C-polysaccharide-complexed CRP to activate complement pathways, 2. the ability of CRP to bind to Fcgamma receptors on phagocytic cells, 3. the ability of CRP to bind to immobilized complement regulator protein factor H which can also be present on pneumococci, and, 4. the ability of CRP to interact with dendritic cells. CRP-treated dendritic cells may well be as host-defensive as CRP alone. An interesting condition for the protective function of CRP is that CRP must be given to mice within a few hours of the administration of pneumococci. CRP does not protect mice if given later, suggesting that CRP works prophylactically but not as a treatment for infection. However, full knowledge of CRP may lead to the development of CRP-based treatment strategies to control pneumococcal infection. Also, because CRP deficiency in humans has not yet been reported, it becomes important to investigate the deficiency of the mechanism of action of CRP in CRP-positive individuals.

Antibody clustering helps refine lupus prognosis

OBJECTIVE

Our aim was to investigate a possible association between patterns of anti-dsDNA antibody isotypes (IgG, IgM, and IgA), rheumatoid factor (RF) isotypes (IgG, IgM, IgA), and IgG anti-C reactive protein (CRP) and systemic lupus erythematosus (SLE) disease activity (SLEDAI).

METHODS

Our study group included 98 patients, 86 women and 12 men, with a mean SLEDAI score of 7.9 +/- 4.1. We divided the patients into 4 groups by the serum anti-dsDNA antibody isotype intensity level.

RESULTS

We found that patients in group 1 (IgG > IgM, 42 patients) had a statistically significantly higher SLEDAI score than group 2 (IgG < IgM, 13 patients) (10.57 +/- 4.62 versus 5.6 +/- 4, P = 0.0012), group 3 (IgG = IgM, 8 patients) (10.57 +/- 4.62 versus 6.2 +/- 1.98, P = 0.04), and group 4 (none, 35 patients) (10.57 +/- 4.62 versus 6 +/- 1.5, P = 0.0001). SLE patients with IgG RF or IgM RF isotype present had a significantly higher SLEDAI score compared with those without IgG RF or IgM RF (10.57 +/- 4.8 versus 7.6 +/- 4.1, P = 0.03, 10.6 +/- 5 versus 7.6 +/- 3.9, P = 0.046). The presence of IgA RF isotype was not associated with a higher SLEDAI score. IgG anti-CRP did not correlate differentially with SLEDAI scores.

CONCLUSIONS

A combination of high-titer IgG anti-dsDNA with a positive RF of IgM isotype may serve as a marker for more active SLE.

C-reactive protein, anti-C-reactive protein antibodies and clinical atherosclerosis

Abstract

There has been considerable interest in the relationship between C-reactive protein (CRP) and atherosclerosis. We have previously demonstrated that individuals, especially those with rheumatoid arthritis and systemic lupus erythematosus, may produce antibodies to CRP. This study was therefore undertaken to determine the possible association between anti-CRP antibodies and atherosclerosis. A total of 103 individuals were identified with or without atherosclerosis, and without clinical rheumatic diseases. They were evaluated with respect to cholesterol, HDL, LDL, high-sensitivity (hs)CRP, and anti-CRP antibody levels, as well as use of statin medications. Individuals with atherosclerosis were much more likely to be taking a statin, and thus have lower lipid levels. However, there was no association between hsCRP or anti-CRP antibody levels with atherosclerosis, statin use, or each other. These observations suggest that anti-CRP antibody is not involved in atherosclerosis, and may represent an epiphenomenon.

Role of apoptosis failure in etiopathogenesis of systemic lupus erythematosus and murine lupus

Apoptosis serves many functions in the homeostasis of multicellular organisms. Defects in apoptosis may lead to clonal expansion and accumulation of autoreactive lymphocytes, which may result in the rare human autoimmune lymphoproliferative syndrome, a mild autoimmune reaction against cells in the blood. Defects in the clearance of apoptotic cells lead to accumulation of dying cells, which may enter later stages of cell death and release their contents, thereby critically contributing to the etiopathogenesis of the autoimmune disease systemic lupus erythematosus. For an efficient therapy of systemic lupus erythematosus, it is necessary to analyze apoptosis and clearance defects and to unravel factors leading to its onset.

Conduct unbecoming: C-reactive protein interactions with a broad range of protein molecules

BACKGROUND

C-reactive protein (CRP), a pentamer composed of five identical 23-kd subunits, is a member of a highly conserved family of proteins known as pentraxins. CRP has been recognized as a risk factor for the development of both the native and transplant-associated forms of atherosclerosis. Understanding the biology of CRP may be relevant to understanding atherosclerosis development and progression.

METHODS

Using Western-blotting techniques, we examined the interactions between native, monomeric and mutationally and chemically modified CRP and a variety of antibodies, monoclonal and polyclonal.

RESULTS

CRP in its denatured monomeric form, but not in its native pentameric conformation, associates promiscuously with IgG molecules, including normal human IgG, as well as with a number of other proteins. This behavior is intrinsic to CRP and is not noted with other pentraxins such as serum amyloid P component or the long pentraxin, PTX3. Monomeric CRP co-localizes with vitronectin in human heart tissue sections.

CONCLUSIONS

We present these findings as cautionary advice, to indicate that characterization of monomeric CRP can be complicated by the propensity of the molecule to interact with a variety of immunoglobulins and other proteins. We also suggest that it is possible that such interactions could serve to eliminate excess of monomeric CRP and/or to scavenge altered, damaged and denatured proteins. These reactivities may be part of a regulatory mechanism to limit inflammation in the arterial wall.

CRP and the disposal of dying cells: consequences for systemic lupus erythematosus and rheumatoid arthritis

C reactive protein (CRP) levels directly correlate with the disease activity of many inflammatory diseases, e.g. sepsis, infection, and various autoimmunopathies such as rheumatoid arthritis (RA). In contrast, insufficient CRP levels are implicated in the development of systemic lupus erythematosus (SLE). This article reports on the level-depended effects of CRP in various diseases. In detail we show that increased and decreased levels of CRP, as demonstrated in patients with RA and SLE, respectively can contribute to disease progression.

Revision in Reference Ranges of Peripheral Total Leukocyte Count and Differential Leukocyte Percentages Based on a Normal Serum C-Reactive Protein Level

BACKGROUND/PURPOSE

A higher total leukocyte count is a predictor of all-cause mortality and cardiovascular morbidity. The currently used reference range for peripheral total leukocyte count is wide (4.5-11.0 x 10(9)/L) and is associated with a low sensitivity in identifying non-infectious chronic diseases. We attempt to revise it based on a normal serum C-reactive protein (CRP) level.

METHODS

Study subjects were participants in a health check program at our hospital between 2000 and 2002. Those whose leukocyte analysis had been checked with the Sysmex Cell Counter NE-9000 were enrolled.

RESULTS

Significantly positive relationships between CRP level and total leukocyte count, neutrophil percentage, and monocyte percentage were found in all subjects (n = 14,114; p < 0.0001). In contrast, CRP level had a significantly inverse correlation with lymphocyte percentage (p < 0.0001). A proposed new reference range for total leukocyte count was estimated based on the data in the normal CRP level group (CRP < 0.1 mg/dL; n = 4839). To rest on the essence of statistics that the range of [mean +/- 2 standard deviations] contains approximately the middle 95% of observations in a sampled population, a new reference range for total leukocyte count was accordingly estimated to be 3.11-8.83 x 10(9)/L.

CONCLUSION

In view of the abundant evidence showing that a higher peripheral total leukocyte count is harmful to health, a down-correction of its upper reference range from the currently used 11.0 x 10(9)/L to the proposed 8.83 x 10(9)/L, based on a normal CRP level, should allow more abnormal health conditions to be identified and promote the usefulness of peripheral leukocyte analysis.

Autoantibodies against Protective Molecules C1q, C-Reactive Protein, Serum Amyloid P, Mannose-Binding Lectin, and Apolipoprotein A1: Prevalence in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of several autoantibodies. Among the multiple factors involved in SLE development, apoptotic defects and impaired clearance of cellular debris have gained considerable interest, as they contribute to autoantigen overload. Several molecules of the innate immunity, also participate in the removal of damaged and apoptotic cells. Among them are C1q, C-reactive protein (CRP), serum amyloid P protein (SAP), mannose-binding lectin (MBL), and apolipoprotein A1 (APO A1). To evaluate the prevalence of autoantibodies against CRP, SAP, MBL, APO A1, and C1q among SLE patients, and their relationship with disease activity, a total of 150 SLE patients were screened for the presence of elevated antibody titers against C1q, CRP, SAP, MBL, and APO A1, utilizing the enzyme-linked immunosorbent assay (ELISA) method. Disease activity was assessed using the ECLAM or SLEDAI scores. The study population comprised two groups of patients: 100 patients with quiescent disease (median ECLAM score 2) comprised the first group, and 50 patients with active disease (median SLEDAI score 16) comprised group 2. Elevated titers of anti-CRP antibodies were significantly elevated only in group 1 (10% versus 4% of controls). Antibodies against SAP were evaluated only among patients in group 1, and were found at a significant high prevalence (20%). Elevated titers of anti-MBL antibodies were significantly elevated only in group 1 (15% versus 3.6%); and antibodies directed against APO A1 were significantly elevated in 21% of group 1, and 50% of group 2 patients. Elevated titers of anti-C1q were evaluated only in group 2, and were found at a significant prevalence of 66%. Significant correlation with disease activity was found only for anti-APO A1 antibodies, and only in group 1. Several patients harbored more than one of the autoantibodies tested. In patients with SLE, autoantibodies directed against protective molecules, that is, acute-phase proteins involved in the disposal of cellular and nuclear debris, can be detected. These autoantibodies may play a pathogenic role in the development or perpetuation of autoimmunity in SLE.

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.