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

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.

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.

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.

Significant elevation of IgG anti-WRN (RecQ3 RNA/DNA helicase) antibody in systemic sclerosis

Werner syndrome, caused by the homologous mutation of RecQ3 RNA/DNA helicase (WRN), is often misdiagnosed as systemic sclerosis (SSc) because of apparent similar skin changes and its relatively high frequency in Japan. The present study was undertaken to determine whether anti-WRN antibodies assayed by specific enzyme-linked immunosorbent assay occur in 41 SSc patients (30 diffuse and 11 limited types) and, if so, to determine any clinical association, such as skin sclerosis. Serum level of IgG anti-WRN antibody in SSc was significantly higher than that from 30 age- and sex-matched normal volunteers (P < 0.001). The serum level of IgG anti-WRN antibody in diffuse type SSc was significantly higher than the limited type (P < 0.05). A significant correlation was observed between serum levels of IgG anti-topoisomerase I antibody and IgG anti-WRN antibody in the same samples from SSc (P < 0.05). Moreover, in 119 normal healthy individuals aged from 0 to 99 years, a statistically significant correlation (P < 0.001) existed between serum level of IgG anti-WRN antibody and advancing age. A significantly higher level of IgG autoantibody specific for WRN detected in diffuse than in limited type SSc and normal may contribute to the pathogenesis of skin sclerosis in SSc.