Antibodies against monomeric C-reactive protein – a promising biomarker of lupus nephritis?

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.

Inflammatory markers in rheumatic diseases

Immune-mediated rheumatic diseases (IMRDs) are a broad group of pathological conditions based on impaired immunological tolerance to one’s own tissues leading to inflammation and irreversible organ damage. Laboratory diagnosis of IMRDs includes a wide range of biomarkers (autoantibodies, acute phase proteins, cytokines, markers of endothelial damage, components of the complement system, immunoglobulins, cryoglobulins, lymphocyte subpopulations, indicators of bone metabolism, apoptosis markers, genetic markers, etc). One of the leading aspects of laboratory diagnosis of IMRDs is the study of the level of inflammation markers in the blood (erythrocyte sedimentation rate, C-reactive protein (CRP), serum amyloid protein (CAA), ferritin, procalcitonin, apolipoprotein AI, calprotectin, etc). The analysis of inflammation markers makes it possible to assess the disease activity, the nature of the progression and the prognosis of the outcomes of a chronic inflammatory process, as well as the effectiveness of the therapy. The review presents the latest data on the role of the most frequently studied inflammatory markers such as CRP, CAA and ferritin.

Monomeric C-Reactive Protein: Current Perspectives for Utilization and Inclusion as a Prognostic Indicator and Therapeutic Target

Monomeric C-reactive protein (mCRP), once thought to be a figment of the imagination and whose biological activity was ascribed to its sodium azide preservative, has now pronounced itself as a critical molecule playing a direct role in mediating many of the acute and chronic aberrant pathological responses to inflammation. In this focused mini review, we describe the currently attributed pathobiological interactions of mCRP in disease, where its tissue and cellular distribution and deposition have recently been clearly characterized and linked to inflammation and other pathway-associated progression of neurological and cardiovascular complications and deleterious outcomes. and focus upon current opinions as to the diagnostic and prognostic potential of mCRP-plasma circulating protein and define the possible future therapeutics including ongoing research attempting to block CRP dissociation with small molecule inhibitors or prevention of cell surface binding directly using antibodies or modified orphan drug targeting directed towards CRP, inhibiting its cellular interactions and signaling activation. There is no doubt that understanding the full influence of the biological power of mCRP in disease development and outcome will be considered a critical parameter in future stratified treatment.

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.

IgG4-related acute interstitial nephritis and the potential role of mCRP autoantibodies: a case report

Background: IgG4-related acute tubulointerstitial nephritis is a type of autoimmune-mediated interstitial nephritis. Recently, autoantibodies against modified C-reactive protein (mCRP) were found to play a pathogenic role in renal diseases through the formation of tubulointerstitial lesions. This is the first case report on the presence of mCRP autoantibodies in a patient with IgG4-associated acute tubulointerstitial nephritis.

Case presentation: A 70-year-old man was admitted with renal dysfunction and a medical history of bile duct stenosis, an inflammatory pancreatic mass, hypertension, and diabetes. On admission, laboratory tests showed higher than normal levels of serum creatinine and IgG4 and lower than normal levels of complements 3 and 4. In addition, the mCRP autoantibody levels were elevated, and the findings of kidney biopsy revealed interstitial nephritis with rich plasma cells in the renal interstitium. The patient was administered prednisone and cyclophosphamide therapy, which resulted in a rapid improvement in renal function.

Conclusion: IgG4-related autoimmune disease should be considered in the diagnosis of patients who have tubulointerstitial nephritis with multisystem involvement. Further, mCRP autoantibodies may be associated with IgG4-related tubulointerstitial nephritis and might be useful as a diagnostic marker of the disease.

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.