Galectin-9 as a biomarker for disease activity in systemic lupus erythematosus

Abstract

Background: Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by elevated interferon (IFN) signature genes. Galectin-9 (Gal-9) is a β-galactoside-binding lectin that is reportedly useful as a biomarker for IFN gene signatures. In a cross-sectional study of Japanese patients with recent-onset SLE, we aimed to determine whether raised serum Gal-9 levels were associated with the disease activity or organ damage seen in SLE patients.

Methods: The current study included 58 Japanese patients with SLE and 31 age-matched healthy individuals. Disease activity and organ damage were assessed using SLE Disease Activity 2000 (SLEDAI-2K) and Systemic Lupus International Collaborating Clinics (SLICC) damage index. Serum and cerebrospinal fluid (CSF) Gal-9 concentrations were quantified using ELISA. Correlation analyses between Gal-9 and clinical parameters including disease activity were performed.

Results: Serum levels of Gal-9 were significantly increased in patients with SLE compared with the control group (16.6 ng/ml, [interquartile range (IQR); 3.6-59.7] versus 4.74 ng/ml, [IQR; 3.0-9.5], p<0.0001). Gal-9 was significantly correlated with disease activity measures in the SLEDAI-2K. Serum Gal-9 levels were significantly greater in patients with SLE-related organ involvement (23.1 ng/ml, [IQR; 5.1-59.7] versus 12.5ng/ml, [IQR; 3.6-39.0], p = 0.013). Whereas there was no difference in serum levels of CXCL10 or M2BPGi between patients with and without SLE-related organ involvement. Serum levels of Gal-9 were significantly higher in SLE patients with active renal involvement determined by BILAG renal score (A-B) compared to those without active renal involvement (C-E). Whereas there was no significant difference in serum levels of Gal-9 between SLE patients with or without active other organ involvements (neurological or hematological) determined by BILAG score. SLE patients with detectable circulating IFN-α had raised serum Gal-9 levels. Levels of Gal-9 were significantly higher in the CSF from patients with recent-onset neuropsychiatric SLE (NPSLE) than in those from non-SLE controls (3.5 ng/ml, [IQR; 1.0-27.2] versus 1.2 ng/ml, [IQR; 0.9-2.1], p = 0.009).

Conclusions: Gal-9 could be a serologic marker of disease activity and organ involvement in SLE patients. Future studies evaluating the role of Gal-9 in the SLE phenotype may provide insights into SLE pathogenesis.

Conflict of interest statement

The study was supported by the Practical Research Project for Rare / Intractable Diseases from Japan Agency for Medical Research and Development, AMED. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Figures

Fig 1. Serum levels of Gal-9 in SLE patients (n = 58) and healthy subjects (n = 31).

Higher Gal-9 levels were found in patients with SLE compared with those in healthy subjects. Median Gal-9 levels (bar) are depicted and statistical analysis was performed using the Mann-Whitney U test.

Fig 2

Correlations between serum levels of Gal-9 and clinical parameters (A: SLEDAI-2K, B: anti-ds-DNA Ab, C: C3 and D: C4) in SLE patients. Serum levels of Gal-9 significantly positively correlated with SLEDAI-2K (A) or anti-ds-DNA Ab (B) and negatively correlated with C3 levels (C). There was no significant correlation between serum levels of Gal-9 and C4 levels (D). Statistics and regression line are represented by the solid line.

Fig 3

Correlations between serum levels of Gal-9 and CXCL 10 (A) or M2BPGi (B) in patients with SLE. Serum levels of Gal-9 significantly correlated with serum levels of CXCL 10 (A) or M2BPGi (B) in patients with SLE. Statistics and regression line are represented by the solid line. Gal-9 = galetin-9, I CXCL10 = C-X-C motif chemokine 10, M2BPGi = Mac-2 binding protein glycosylation isomer.

Fig 4

10 (A) or M2BPGi (B) and SLEDAI-2K in patients with SLE. There was no significant correlation between serum levels of Gal-9 and CXCL 10 (A). Serum levels of M2BPGi (B) significantly correlated with SLEDAI-2K in SLE patients. Statistics and regression line are represented by the solid line. Gal-9 = galetin-9, CXCL10 = C-X-C motif chemokine 10, M2BPGi = Mac-2 binding protein glycosylation isomer.

Fig 5. Serum biomarkers in SLE patients with or without organ damage.

We compared serum levels of biomarkers (A: Gal-9, B: CXCL 10, C: M2BPGi) between SLE patients with any organ damage (i.e., SDI ≥ 1) and those without organ damage (i.e., SDI = 0). Raised serum Gal-9 levels were found in SLE patients with any organ damage compared with those without organ damage (A). No significant difference in CXCL 10 (B) or M2BPGi (C) levels was observed between SLE patients with and without any organ damage. SDI: Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index.

Fig 6. Serum levels of Gal-9 in SLE patients with or without active organ involvements.

We compared serum levels of Gal-9 between SLE patients with active organ involvements (BILAG general, renal, neurological, hematological domains; A-B) and without active organ involvement (BILAG; C-E).

Fig 7. Serum Galectin-9 (Gal-9) levels in SLE patients with detectable circulating IFN-α.

We compared serum levels of Gal-9 between SLE patients with and those without detectable circulating IFN-α. Raised serum Gal-9 levels were found in SLE patients with detectable circulating IFN-α compared with those without detectable circulating IFN-α. Median Gal-9 levels (bar) are depicted and statistical analysis was performed using the Mann-Whitney U test.

Fig 8. Longitudinal changes in serum Gal-9 concentrations in 5 patients with active SLE before and after immunosuppressive treatments.

Paired samples from the same subjects were compared by Wilcoxon signed-rank test. Gal-9 = galetin-9.

Fig 9. Levels of Galectin-9 (Gal-9) in cerebrospinal fluid (CSF).

Samples of CSF were obtained from patients with neuropsychiatric systemic lupus erythematosus (NPSLE, n = 18) and non-SLE controls (n = 6). Each point represents an individual patient. Median Gal-9 levels (bar) are depicted and statistical analysis was performed using the Mann-Whitney U test.

Fig 10. Relationship between cerebrospinal fluid (CSF) Gal-9 and serum Gal-9 in NPSLE patients and controls.

Relationship between cerebrospinal fluid (CSF) Gal-9 and serum Gal-9 were evaluated in patients with NPSLE and non-SLE controls. NPSLE: neuropsychiatric systemic lupus erythematosus.