Serological biomarkers distinguishing cutaneous lupus erythematosus (CLE) and systemic lupus erythematosus (SLE) may help track CLE patients at risk for progression to SLE. Thus, we compared CLE and SLE sera concentrations of CXCL9 and CXCL10, two chemokines previously demonstrated to be upregulated in CLE1 and SLE,2 and assessed their ability to discriminate between patient groups.
Serum samples from patients with CLE-only (CLE+/SLE−) (n=48), CLE and SLE (CLE+/SLE+) (n=17), SLE without CLE (CLE−/SLE+) (n=26), and controls (n=29) were collected at the University of Texas Southwestern Medical Center and Parkland Memorial Hospital (Table 1). Patients with ≥4 American College of Rheumatology (ACR) SLE criteria were classified as SLE. Patients with CLE-isolated disease were diagnosed by skin biopsy and had <4 ACR SLE criteria. Seventeen SLE patients had a concomitant diagnosis of CLE. Exclusion criteria included concomitant autoimmune disease, chronic infection, or active malignancy. Serum levels of chemokines were measured using ELISA (R&D Systems, Minneapolis, MN), and compared using the Mann-Whitney or Kruskal-Wallis test. The ability of the chemokines to discriminate between CLE and SLE patients was measured using the area under the receiver operating characteristics (ROC) curve.
Table 1:
Patient demographics and clinical characteristics
| CLE+/SLE− (n=48) | CLE+/SLE+ (n=17) | CLE−/SLE+ (n=26) | Controls (n=29) | |
|---|---|---|---|---|
| Age, median (IQR) | 48 (39–58) | 41 (29.5–51) | 28 (25.6–34.4) | 44.1 (35.1–55.7) |
| Sex, n (%) | ||||
| Female | 35 (73%) | 14 (82%) | 26 (100%) | 22 (76%) |
| Male | 13 (27%) | 3 (18%) | 0 (0%) | 7 (24%) |
| Race/Ethnicity, n (%) | ||||
| African American | 30 (63%) | 14 (82%) | 7 (27%) | 18 (62%) |
| Caucasian | 13 (27%) | 1 (6%) | 5 (19%) | 9 (31%) |
| Hispanic | 4 (8%) | 2 (12%) | 12 (46%) | 1 (3%) |
| Asian | 1 (2%) | 0 (0%) | 2 (8%) | 1 (3%) |
| ACR SLE Criteria, n (%) | N/A | |||
| Malar Rash | 0 (0%) | 5 (29%) | 0 (0%) | |
| Discoid Rash | 42 (88%) | 17 (100%) | 0 (0%) | |
| Photosensitivity | 32 (67%) | 15 (88%) | 9 (35%) | |
| Oral Ulcers | 1 (2%) | 8 (47%) | 5 (19%) | |
| Arthritis | 0 (0%) | 11 (65%) | 10 (38%) | |
| Pleuritis/Pericarditis | 0 (0%) | 3 (18%) | 5 (19%) | |
| Renal disorder | 0 (0%) | 9 (53%) | 26 (100%) | |
| Neurologic disorder | 0 (0%) | 0 (0%) | 2 (8%) | |
| Hematologic disorder | 11 (23%) | 7 (41%) | 10 (38%) | |
| Immunologic disorder | 2 (4%) | 14 (82%) | 21 (81%) | |
| Positive anti-nuclear | 13 (27%) | 17 (100%) | 20 (77%) | |
| Antibody | ||||
| Predominant CLE Subtype, n (%)^ | N/A | N/A | ||
| Localized DLE | 29 (60%) | 3 (18%) | ||
| Generalized DLE | 13 (27%) | 13 (71%) | ||
| SCLE | 6 (13%) | 0 (0%) | ||
| Medications, n (%) | N/A | |||
| None | 16 (33%) | 0 (0%) | 2 (8%) | |
| Topical steroids | 15 (31%) | 0 (0%) | 0 (0%) | |
| Anti-malarials | 13 (27%) | 4 (24%) | 4 (15%) | |
| Other immunosuppresants | 4 (8%) | 13 (76%) | 20 (77%) | |
| CLASI-A, median (IQR) | 4 (3–9) | 11 (6–21)* | N/A | N/A |
| CLASI-D, median (IQR) | 8 (2–13) | 16 (11–28)* | N/A | N/A |
CLASI-A and CLASI-D data available for 15 SLE patients with concomitant diagnosis of CLE.
One CLE+/SLE+ patient had a diagnosis of DLE per chart review, but information regarding DLE subtype was not available.
Abbreviations: CLASI-A, cutaneous lupus erythematosus disease area and severity index – activity; CLASI-D, cutaneous lupus erythematosus disease area and severity index – damage; CLE, cutaneous lupus erythematosus; DLE, discoid lupus erythematosus; IQR, interquartile range; LE – lupus erythematosus; SCLE – subacute cutaneous lupus erythematosus; SLE – systemic lupus erythematosus
CLE+/SLE− sera had elevated CXCL9 and CXCL10 levels versus controls (CXCL9: median: 50.91 pg/mL (interquartile range (IQR): 32.8–122.1 pg/mL) vs. 20.54 pg/mL (12.7–34.4 pg/mL) (p<0.0001), CXCL10: 220.77 pg/mL (132–360.1 pg/mL) vs. 124.12 pg/mL (89.5–149.4 pg/mL) (p=0.002)). Serum levels of CXCL10 in CLE+/SLE+ patients (473.9 pg/mL (327.5–1978.8 pg/mL)) and CLE−/SLE+ patients (642.3 pg/mL (398.5–1561.3 pg/mL)) were significantly elevated compared to CLE+/SLE− patients (p<0.003) and healthy controls (p<0.0001). CXCL9 levels were significantly higher in CLE+/SLE+ patients (88.5 pg/mL (77.0–138.0 pg/mL)) and CLE−/SLE+ patients (57.7 pg/mL (24.1–107.5 pg/mL)) than controls (p<0.0001) but not CLE+/SLE− patients (Figure 1A–1B). ROC analysis was performed to distinguish CLE+SLE+ and CLE+SLE− patients for CXCL9 and CXCL10 (Figure 1C–1D). CXCL10 levels in CLE+/SLE+ and CLE+/SLE− patients yielded an area under curve (AUC) of 0.83 (95% confidence interval: 0.72–0.93) (p<0.0001).
Figure 1. CXCL9 and CXCL10 serum levels in SLE and CLE patients and healthy control patients.
(A-B) Serum levels of CXCL9 (A) and CXCL10 (B) were compared between healthy, CLE+/SLE−, CLE+/SLE+, and CLE−/SLE+ patients using Kruskal-Wallis test. **: p≤0.01, ***: p<0.001, ****: p<0.0001. Data points corresponding to CLE patients that were classified as discoid lupus erythematosus (DLE) are indicated as open dots. (C-D) ROC curves for CXCL9 (C) and CXCL10 (D) levels in CLE and SLE patients. Abbreviations: CLE: cutaneous lupus erythematosus; ROC: receiver operating characteristic; SLE: systemic lupus erythematosus.
These results highlight the potential utility of CXCL10 as a biomarker to distinguish SLE and CLE patients. In CLE, CXCL10 induces Th1-based inflammation and recruitment of CXCR3+ T cells and interferon-associated cytokines into the skin, promoting tissue injury.1 Increasing sera levels of CXCL10 from controls to CLE+/SLE− patients to CLE+/SLE+ and CLE−/SLE+ patients demonstrates the potential spread of Th1-induced inflammation from skin to systemic levels. Increased CXCL10 levels in SLE patients have been shown to come from both peripheral blood and other end organs.3 Thus, we postulate that increases in CXCL10 over time may predict the onset of SLE for CLE patients. In contrast, CXCL9 did not distinguish CLE and SLE patients as well as CXCL10. The lack of significant CXCL9 up-regulation from end organs in human lupus patients may explain the smaller difference in CXCL9 levels between CLE and SLE patients.4, 5 While this study was limited by its cross-sectional single center design, small sample size, larger longitudinal studies are needed to confirm our hypothesis that CXCL10 is a biomarker that stratifies CLE from SLE, and track systemic disease spread for CLE patients.
Acknowledgments:
We would like to acknowledge Rebecca Vasquez, Andrew Kim, Daniel Grabell, Noelle Teske, and Tina Vinoya for recruiting patients. The authors would like to thank participants of the UTSW Cutaneous Lupus Erythematosus Registry for their contributions to lupus research.
Funding sources:
The research reported in this publication was supported by National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under Award Number K23AR061441 (BFC). R.S. is supported by the George M. O’Brien Kidney Research Core Center (US National Institutes of Health grant P30DK079328). The content is solely the responsibility of the authors and does not necessarily represent the official views of the University of Texas Southwestern Medical Center at Dallas and its affiliated academic and health care centers and the National Institutes of Health.
Footnotes
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IRB approval status: This study was approved by the Institutional Review Board at University of Texas Southwestern Medical Center, Dallas, TX.
Conflict of Interest Disclosure: Dr. Chong is an investigator for Pfizer Incorporated, Biogen Incorporated, Daavlin Corporation, and Amgen Incorporated, and a consultant for Viela Bio, Beacon Bioscience, Bristol Meyers Squibb, EMD Serono, and Principia Biopharma. The other authors have no conflicts of interest. This manuscript is not simultaneously being submitted elsewhere, and no portion of the data has or will be published in proceedings or transactions of meetings or symposium volumes.
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