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ORIGINAL ARTICLE
Year : 2022  |  Volume : 35  |  Issue : 1  |  Page : 110-115

Assessment of systemic lupus erythematosus disease activity and lupus nephritis flare using anti-nucleosome and anti-C1q antibodies


1 Department of Internal Medicine, Faculty of Medicine, Tanta University, Tanta, Egypt
2 Department of Clinical Pathology, Faculty of Medicine, Tanta University, Tanta, Egypt

Date of Submission18-Aug-2021
Date of Decision28-Sep-2021
Date of Acceptance04-Oct-2021
Date of Web Publication18-Apr-2022

Correspondence Address:
Waleed Elrefaey
Internal Medicine MD, Department of Internal Medicine Hospital, Tanta University Hospitals, Elgeish Street, Tanta, Gharbia 31111
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_144_21

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  Abstract 


Objectives
To evaluate serum levels of anti-nucleosome and anti-C1q in systemic lupus erythematosus (SLE) patients, and their correlation with disease activity and lupus nephritis (LN) flare.
Background
SLE is a common chronic multiorgan affection autoimmune disease with loss of self-tolerance and unpredictable activity. Increased serum anti-nucleosome and anti-C1q levels may play pathogenic roles in SLE activity and LN immune aberration and disease flare.
Patients and methods
The study was carried out on 120 participants, 80 SLE patients and 40 non-SLE individuals as a control group. Of these, 55 patients were diagnosed as LN patients by kidney biopsy before enrollment into the study. Anti-nucleosome antibodies and anti-C1q were determined using a quantitative enzyme-linked immunosorbent assay.
Results
Anti-nucleosome and anti-C1q serum levels were statistically significantly high in SLE patients in comparison to the control group and statistically significantly high in active SLE patients (111.43 ± 43.97 and 68.62 ± 22.99 U/ml, respectively) than inactive SLE patients. They have significant positive correlations with the SLE disease activity index score (P < 0.001) and have a high sensitivity and specificity for SLE diagnosis and its activity (P < 0.001). Anti-nucleosome and anti-C1q serum levels were statistically significantly high in LN (113.89 ± 43.87 and 68.61 ± 24.49 U/ml, respectively) than in non-LN patients (P = 0.004, P < 0.001, respectively) with statistically significant positive correlations with SLE disease activity index-renal domain score (P < 0.001). They have high sensitivity and specificity for the diagnosis of active LN (P = 0.004, P < 0.001, respectively).
Conclusions
Anti-nucleosome and anti-C1q can be used as markers for the diagnosis of SLE disease activity and LN flare with high sensitivity and specificity.

Keywords: anti-C1q, anti-nucleosome, lupus nephritis, systemic lupus erythematosus disease activity index, systemic lupus erythematosus


How to cite this article:
Elrefaey W, Gawaly AM, Hagag RY, Mohammed HA, Abdelnaby AY, Aboelnasr MS. Assessment of systemic lupus erythematosus disease activity and lupus nephritis flare using anti-nucleosome and anti-C1q antibodies. Menoufia Med J 2022;35:110-5

How to cite this URL:
Elrefaey W, Gawaly AM, Hagag RY, Mohammed HA, Abdelnaby AY, Aboelnasr MS. Assessment of systemic lupus erythematosus disease activity and lupus nephritis flare using anti-nucleosome and anti-C1q antibodies. Menoufia Med J [serial online] 2022 [cited 2024 Mar 29];35:110-5. Available from: http://www.mmj.eg.net/text.asp?2022/35/1/110/343102




  Introduction Top


Systemic lupus erythematosus (SLE) is an autoimmune inflammatory disease caused by disturbance of the immune system with loss of self-tolerance resulting in multiorgan dysfunction [1]. One of the most serious complications of SLE is lupus nephritis (LN), which affects a significant proportion of patients with increased morbidity [2] and 10% incidence of end-stage renal disease [3].

This disease is characterized by the variability in severity, and flares are common in the disease course and contribute significantly to organ dysfunction and poor outcome [4]. It is recommended to monitor SLE through validated disease activity and chronicity indices, including physician global assessment [5]. SLE disease activity index (SLEDAI) and SLE disease activity index-renal (SLEDAI-R) domain are clinical indices used for SLE and LN activity assessment [6].

C1q functions to wash up auto-antigens [7], and nucleosomes are the basic element of chromatin [8]. Antibodies against these two components could be valuable for early diagnosis and follow up of SLE patients [9].

This study was conducted to evaluate serum levels of anti-nucleosome and anti-C1q antibodies in SLE patients, and their correlation with lupus activity and LN flare.


  Patients and methods Top


This is a cross-sectional study that was conducted on 120 individuals, 80 SLE patients and 40 non-SLE participants as a healthy control group. The 80 patients were diagnosed to have SLE according to the Systemic Lupus International Collaborating Clinics (SLICC) classification criteria, and 55 of them were diagnosed as LN patients by kidney biopsy before enrollment into the study. Their age ranged from 19 to 50 years and included 18 males and 62 females. The control group age ranged from 19 to 43 years and included 12 males and 28 females. The study was carried out within the period from January 1, 2020 to June 30, 2020.

SLEDAI score is used to assess SLE disease activity. The patients were considered active if the score was 8 or more. SLEDAI-R domain score was used to assess LN activity, including four parameters: proteinuria, hematuria, pyuria, and urinary casts. A score of 4 or more is an indicator of active LN [5].

All participants were subjected to full medical history taking, clinical assessment, and laboratory investigations including complete blood count, C-reactive protein, erythrocyte sedimentation rate, liver function tests (serum bilirubin, liver enzymes, serum albumin), serum creatinine, blood urea, estimated glomerular filtration rate, 24-h urine protein measurement, and lipid profile. Immunological profile was done including antinuclear antibodies, anti-double stranded DNA antibodies, and complements 3 and 4.

Anti-nucleosome antibodies were determined using a quantitative enzyme-linked immunosorbent assay (ELISA) (according to the manufacturer' instructions from IMTeC Human, Germany). The ELISA plate was precoated with nucleosomes isolated from human cell cultures. The calculation range is 0–200 U/ml, with negative results less than 20 U/ml, and positive results more than or equal to 20 U/ml.

Anti-C1q antibodies were determined using a quantitative ELISA, which is based on an indirect enzyme-linked immune reaction (according to the manufacturer's instructions from IMTeC Human, Germany). Specific antibodies in the patient serum sample attach to the antigen coated on the surface of the reaction wells. A washing step eliminates unbound serum or plasma components after incubation. The calculation range is 0–100 U/ml, with positive results more than or equal to 10 U/ml and negative results less than 10 U/ml.

Declarations

Ethics Committee of the Faculty of Medicine, Tanta University approved this research work. The committee's reference number is 31886/11/17. The study was performed in line with the principles of the Declaration of Helsinki. Written informed consent for participation was taken from all participants and privacy of the data was greatly considered.

Statistical analysis

The collected data were organized, tabulated, and statistically analyzed using the Statistical Package for the SPSS version 20, IBM corp., New York, USA. Measurement of data consistent with normal distribution was expressed as mean ± SD. Statistical differences between groups were tested using χ2 test for qualitative variables, Student's t test between two groups of numerical (parametric) data. Kruskal–Wallis test was used to compare between more than two groups of numerical (nonparametric) data, followed by Mann–Whitney for multiple comparisons. Spearman's correlation is used to show the relationship between different variables. P values less than 0.05 were considered statistically significant.


  Results Top


Eighty SLE patients and 40 healthy participants (control group) were included in this study. Their demographic, clinical, and laboratory data are expressed in [Table 1].
Table 1: Demographic, clinical, and laboratory data in the studied groups

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There was no statistically significant difference between the patients and control group regarding age and sex. No statistically significant differences were found as regards liver function tests and lipid profile between the two groups. Serum creatinine, blood urea, and 24 h urinary protein were significantly increased, and estimated glomerular filtration rate was significantly decreased in LN patients when compared with the control group.

According to SLEDAI score, 52 patients had SLE disease activity and 28 patients had inactive SLE. According to SLEDAI-R score, 38 patients had active LN and 17 patients had inactive LN.

As regards immune profile, serum antinuclear antibodies and anti-double stranded DNA antibody levels were significantly higher and complement 3 level was significantly lower in the SLE patients' group in comparison to the control group. Anti-C1q antibody (59.07 ± 25.85 U/ml, P < 0.001) and anti-nucleosome antibody serum levels (87.47 ± 53.22 U/ml, P < 0.001) were significantly higher in the SLE patient group in comparison to the control group (4.87 ± 2.47 and 4.50 ± 3.24 U/ml), respectively.

Regarding SLE activity, complement 3 level was statistically significantly lower in active than in inactive lupus patients (P = 0.013). Anti-C1q antibody (68.62 ± 22.99 U/ml, P < 0.001) and anti-nucleosome antibody levels (111.43 ± 43.97 U/ml, P < 0.001) were significantly higher in active SLE patients than in inactive SLE patients (36.78 ± 17.41 and 31.56 ± 20.27 U/ml), respectively.

Anti-C1q antibody (68.61 ± 24.49 U/ml, P = 0.004) and anti-nucleosome antibody serum levels (113.89 ± 43.87 U/ml, P < 0.001) were statistically significantly higher in LN patients than non-LN patients (44.75 ± 21.51 and 47.83 ± 40.46 U/ml), respectively.

There were statistically significant positive correlations between SLEDAI score and anti-C1q antibody (r = 0.710, P < 0.001) and anti-nucleosome antibody levels (r = 0.676, P < 0.001). Moreover, there were significant positive correlations between SLEDAI-R score and anti-C1q antibody (r = 0.615, P < 0.001) and anti-nucleosome antibody levels (r = 0.607, P < 0.001).

As regards the diagnostic utility of these antibodies for SLE, anti-C1q antibody has a sensitivity of 86.7%, specificity of 93.3%, positive predictive value of 92.9%, and negative predictive value of 87.5%. The anti-nucleosome antibody has a sensitivity of 83.3%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 85.7%.

To quantify the use of both antibodies for the diagnosis of SLE activity versus SLEDAI score, a receiver-operating characteristic curve was constructed. Anti-C1q antibody has a sensitivity of 90.5%, specificity of 100%, and an area under the curve equal to 0.905 at a cutoff value of 60 U/ml (P < 0.001) [Figure 1]. Anti-nucleosome antibody has a sensitivity of 90%, specificity of 100%, and area under curve = 0.921 at a cutoff value of 76 U/ml (P < 0.001) [Figure 2].
Figure 1: ROC curve for anti-C1q in relation to SLE activity (SLEDAI). ROC, receiver-operating characteristic; SLE, systemic lupus erythematosus; SLEDAI, systemic lupus erythematosus disease activity index.

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Figure 2: ROC curve for anti-nucleosome in relation to SLE activity (SLEDAI). ROC, receiver-operating characteristic; SLE, systemic lupus erythematosus; SLEDAI, systemic lupus erythematosus disease activity index.

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In addition, to quantify the use of both antibodies for the diagnosis of active LN versus SLEDAI-R score, a receiver-operating characteristic curve was constructed. Anti-C1q antibody has a sensitivity of 88.9%, specificity of 75%, and an area under the curve of 0.812 at a cutoff value of 60 U/ml (P = 0.004) [Figure 3]. Anti-nucleosome antibody has a sensitivity of 88.9%, specificity of 75%, and an area under the curve of 0.859 at a cutoff value of 76 U/ml (P < 0.001) [Figure 4].
Figure 3: ROC curve for anti-C1q in relation to lupus nephritis activity (SLEDAI-R). ROC, receiver-operating characteristic; SLEDAI-R, SLE disease activity index-renal.

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Figure 4: ROC curve for anti-nucleosome in relation to lupus nephritis activity (SLEDAI-R). ROC, receiver-operating characteristic; SLEDAI-R, SLE disease activity index-renal.

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  Discussion Top


SLE is a classic example of systemic autoimmune disease affecting multiple organs. Pathogenesis of SLE is complex but the major two players are antibodies and T cells auto activation [10]. SLE patients with activity have increased anti-C1q autoantibodies serum levels that play a valuable role in SLE pathogenesis through peripheral lymphocyte apoptosis [11]. Other important antibodies in the pathogenesis of SLE are anti-nucleosome antibodies, which initiate the T cell-mediated inflammatory response by the hapten-carrier-like system to produce numerous autoantibodies [7].

This study aimed to measure the serum levels of anti-nucleosome and anti-C1q antibodies in SLE patients, and to evaluate their diagnostic utility for SLE and their correlation with SLE activity and active LN.

In this study, anti-C1q antibody level was statistically significantly higher in SLE patients' group in comparison to the control group (P < 0.001) with a sensitivity of 86.7% and specificity of 93.3% and was significantly higher in active SLE patients than inactive SLE patients (P < 0.001). Also, its level was higher in LN patients than non-LN SLE patients (P = 0.004).

Orbai et al. [12] agreed with these findings, and found that anti-C1q antibody serum level was significantly higher in SLE patients than the healthy control group (P < 0.001). Results of Trad et al. [13] were consistent with our results, as they found a higher prevalence of anti-C1q antibody in SLE patients and it was found in 53 (54.1%) patients with SLE, three (5%) patients with rheumatoid arthritis, and in six (9.3%) healthy controls.

Moreover, our findings agree with Moroni et al. [14], who noticed that anti-C1q antibody level was statistically significantly higher in SLE patients (52.6%), active SLE patients (78.4%), and in LN patients (85.7%) in comparison with non-SLE patient controls, patients with inactive SLE, and non-LN, respectively. They suggested that these serological antibodies for the identification of SLE patients with active LN and active SLE disease are reliable promising markers. Also, Pradhan et al. [15] agreed with our results and observed that anti-C1q antibody level has 58.3% sensitivity in SLE and was significantly higher in patients with LN as compared with SLE patients without LN (P < 0.05).

In this study, there was a significant positive correlation between anti-C1q antibody level with SLEDAI score (P < 0.001) and SLEDAI-R domain score (P < 0.001). These findings were consistent with Mok et al. [16] and Zhang et al. [17], who found that anti-C1q antibody titer had a significant positive correlation with SLEDAI score (P < 0.001 and 0.05), respectively. Also, Omran et al. [18] found a significant correlation between anti-C1q and the SLEDAI score (P < 0.035) and the SLEDAI-R (P < 0.025). On the other hand, Trad et al. [13] and Meyer et al. [19] disagreed with our findings and noticed no correlation between anti-C1q antibody level with SLEDAI score.

In our study, anti-nucleosome antibody level was statistically significantly higher in SLE patients' group in comparison to the control group (P < 0.001) with a sensitivity of 83.3% and specificity of 100% and was significantly higher in active SLE patients than inactive SLE patients (P < 0.001). Also, its level was higher in LN patients than non-LN SLE patients (P < 0.001).

In agreement with our findings, Pradhan et al. [20] found that anti-nucleosome antibody had 83% sensitivity in SLE patients. Also, Putova et al. [21] studied its serum level in 128 SLE patients and found that 73% of patients were positive, and Braun et al. [22] observed that it had a sensitivity of 64.1% and a specificity of 99.2% for SLE diagnosis.

In concordance with our results, Hung et al. [23] noticed that anti-nucleosome antibody level was significantly higher in patients with LN as compared with nonrenal SLE patients (P < 0.05). In the current study, the anti-nucleosome antibody has a sensitivity of 83.3% and a specificity of 100%. Cervera et al. [24] agreed with this finding and found that it has a significantly high sensitivity (81%) for the diagnosis of LN.

In this study, there was a significant positive correlation between anti-nucleosome antibody level with SLEDAI score (P < 0.001) and SLEDAI-R score (P < 0.001). In consistence with these findings, Mok et al. [16] found a significant positive correlation between anti-nucleosome level and SLEDAI score (P < 0.001), but no significant correlation with renal SLEDAI score.

In contrast to our results, Saigal et al. [25] observed that anti-nucleosome antibody was not superior to anti-ds DNA antibody in the assessment of SLE activity with a weaker correlation to SLEDAI score. Also, Lima et al. [26] found that there was no association between its level and disease activity in SLE, and Živković et al. [27] concluded that its specificity in the identification of activity of SLE disease and lupus flare was limited.


  Conclusion Top


Anti-nucleosome and anti-C1q antibodies can be used as useful markers for the diagnosis of SLE and disease activity because of their high sensitivity and specificity and their significant positive correlation with SLE and LN activity. Their levels are higher in LN patients than nonrenal SLE patients with high sensitivity for LN flare and lower specificity than that for SLE activity.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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