Urinary soluble CD163 is a good biomarker for renal disease activity in lupus nephritis.

OBJECTIVES

Activated macrophages expressing CD163 (M2) are the most abundant macrophage subtype in renal biopsies from lupus nephritis (LN) patients. We studied the role of proteolytically cleaved soluble CD163 (sCD163) as a biomarker of LN disease activity.

METHODS

SLE patients were classified as active LN (AN), inactive disease (ID), and active non-renal disease (ANR). Urine and plasma samples were collected at baseline from all patients and at 3 monthly follow-up from AN patients. sCD163 was measured by ELISA. Urine values were normalized to urinary creatinine excretion and expressed as pg/mg. Urine samples from 25 healthy controls (HC) and 20 rheumatoid arthritis patients served as disease controls (DC).

RESULTS

Among the 122 patients studied (114 females, 57 AN, 42 ID, 23 ANR), baseline median urinary sCD163 in the AN group (114.01 pg/mg) was significantly higher (p < 0.001) as compared with ID (10.34 pg/mg), ANR (3.82 pg/mg), HC (0 pg/mg), and DC (7.56 pg/mg) groups and showed modest correlation with renal SLEDAI (r = 0.47; p < 0.001). Urinary sCD163 performed the best on receiver operating characteristics (ROC) analysis (AUC = 0.76) at baseline to differentiate between AN and ANR as compared with plasma sCD163, anti-ds DNA antibodies, and C3 and C4. In follow-up study, urinary sCD163 decreased significantly (p < 0.001) in AN patients at 3 (22.07 pg/mg), 6 (12.7 pg/mg), 9 (11.09 pg/mg), and 12 months (7.2 pg/mg). In 4 patients who had either relapse or developed CKD, urinary sCD163 levels correlated with the changing disease activity.

CONCLUSIONS

Urinary sCD163 is a good biomarker of LN disease activity. Key Points • Urinary sCD163 levels are raised in patients with active lupus nephritis and correlate with renal SLEDAI. • Urinary sCD163 levels fall after treatment and may be helpful in monitoring response to therapy in lupus nephritis.