sCD163

Urinary soluble CD163 (u-sCD163) is the soluble form of the CD163 protein, a transmembrane glycoprotein expressed exclusively on monocytes and macrophages. Under pro-inflammatory stimuli, CD163 is enzymatically cleaved from the cell surface and released in its soluble form (sCD163) into the extracellular compartment.

In the context of active glomerular inflammation – such as in autoimmune nephritides – macrophages infiltrating the glomerulus release sCD163 directly into the urinary space, leading to a significant increase in u-sCD163 levels. By contrast, its urinary concentration in healthy individuals is very low or undetectable.

sCD163 is emerging as a promising non-invasive biomarker for the diagnosis, monitoring and stratification of glomerular inflammatory activity, particularly in two clinical settings:

• ANCA-associated vasculitides (AAV): in patients with active renal involvement, urinary sCD163 levels are significantly higher than in patients in remission, disease controls without renal involvement and healthy subjects. The marker appears to be specific for active glomerular injury, as it does not increase in the absence of renal involvement, even in systemic vasculitis.
• Lupus nephritis (LN): elevated sCD163 levels have been observed in patients with active proliferative forms (ISN/RPS classes III and IV), suggesting a direct correlation with histologic disease activity.

Therefore, sCD163 may represent a useful diagnostic and prognostic tool to identify active phases of glomerular inflammation, monitor response to immunosuppressive therapy and guide clinical management, potentially reducing the need for repeat kidney biopsies.