Serum and urinary soluble CD163 in children with active lupus nephritis.

BACKGROUND

Lupus nephritis (LN) is a major contributor to morbidity and death in systemic lupus erythematosus (SLE), particularly in children. CD163 is a macrophage- and monocyte-specific receptor that can be cleaved and released as soluble CD163 (sCD163). Both circulating and urinary sCD163 reflect macrophage activation and are elevated in inflammatory and autoimmune conditions, highlighting their potential as biomarkers of renal inflammation. There is unmet need to develop a set of biomarkers that can accurately reflect disease activity and prognosis and differentiate active from non-active cases. In this context, we aimed to evaluate serum and urinary sCD163 levels in children with active LN and to examine their association with established clinical and laboratory markers of SLE activity. Additionally, we explored differences in sCD163 levels between patients with renal versus extrarenal SLE activity and between inflammatory LN and non-inflammatory chronic kidney disease (CKD).

METHODS

We enrolled 60 pediatric participants in four qual groups, Group 1: patients with active LN, group 2: SLE non-LN with active extrarenal disease, determined by SLEDAI and BILAG-2004 indices, group 3: non-lupus CKD, and group 4: healthy matched controls. Serum and urine levels of sCD163 were determined in all participants by ELISA.

RESULTS

Serum and urinary sCD163 levels differed significantly among the study groups, with the highest levels in active LN. Patients with active renal BILAG scores A or B had significantly higher sCD163 levels than those with BILAG E, while no significant differences across histopathological classes. Serum sCD163 correlated negatively with eGFR and positively with proteinuria, whereas urinary sCD163 correlated positively with SLEDAI, proteinuria, and prednisolone dose. Both serum and urinary sCD163 distinguished renal from extrarenal SLE activity and LN from non-inflammatory CKD, with complete separation between groups (AUC = 1). No significant correlation was found between serum and urinary sCD163.

CONCLUSION

Both sCD163 levels were associated with LN activity and differed from levels in extrarenal SLE and non-inflammatory CKD, suggesting that sCD163 may serve as a potential biomarker of kidney inflammation in pediatric SLLE patients.