Urine and serum interleukin 35 as potential biomarkers of lupus nephritis

Introduction
Lupus nephritis (LN) is considered a serious manifestation of systemic lupus erythematosus (SLE). Therefore, a reliable non-invasive biomarker is a priority for monitoring renal involvement instead of the kidney biopsy. Interleukin 35 (IL-35) has an immunosuppressive and anti-inflammatory role in many autoimmune diseases. However, its role in LN still needs to be elucidated.
Aim of the study: To evaluate urine and serum levels of IL-35 in SLE patients with LN and without nephritis identifying their potential as biomarkers of renal involvement.

Material and methods
Urine and serum levels of IL-35 were measured in 42 SLE patients, divided into 22 with LN and 20 without LN, and 20 matched healthy controls using enzyme-linked immunosorbent assay (ELISA). SLE disease activity was assessed for patients by the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K).

Results
Levels of serum and urine IL-35 were significantly higher (p < 0.001) in the LN group compared with those without LN and with controls. In LN patients, a strong correlation (p < 0.001) was observed between serum and urine IL-35 levels with SLEDAI-2K score (r = 0.677 and 0.806 respectively). Furthermore, proteinuria had a strong and significant correlation (p  0.001) with serum and urinary IL-35 levels in the patients with LN. Serum IL-35 had 90.9% sensitivity and 85% specificity while urine IL-35 had 95.5% sensitivity and 75% specificity to differentiate LN from healthy individuals.

Conclusions
Urine and serum IL-35 may aid in assessment of renal involvement in SLE patients, serving as potential biomarkers of LN.