Longitudinal assessment of monocyte chemoattractant protein-1 in lupus nephritis as a biomarker of disease activity

Urinary MCP-1 (uMCP-1) levels reflect lupus nephritis (LN) disease activity. However, long-term prospective studies evaluating it as a biomarker are lacking. SLE patients with active nephritis (AN), active disease without nephritis (ANR), and inactive disease (ID) were enrolled. AN patients were followed up every 3 months for 1 year. Urine and serum samples were collected at baseline from all and at follow-up visits in AN group. Urine samples from healthy subjects (HC), rheumatoid arthritis (RA), and diabetic nephropathy (DM) patients (20 each) served as controls. Serum (sMCP-1) and uMCP-1 was measured using ELISA. Urinary values were normalized for creatinine excretion. Nonparametric tests were used. A total of 121 SLE patients were enrolled. Baseline uMCP-1 was significantly higher in AN as compared to ANR, ID, HC, and RA (p < 0.001), but it was not different from DM and showed good correlation with rSLEDAI and SLEDAI (r = 0.52 and 0.47, p < 0.001) but not with sMCP-1. On ROC analysis to differentiate between AN and ANR, uMCP-1 performed better than sMCP-1, anti-dsDNA antibodies, C3 and C4. uMCP-1 and not sMCP-1 decreased significantly at all follow-up visits (p < 0.001). uMCP-1 remained persistently elevated in a patient who developed CKD and rose before conventional markers in two patients with relapse of LN. uMCP-1 correlates well with LN disease activity and helps differentiate between AN and ANR patients. Its levels fall with treatment and may have a potential to predict poor response and relapse of LN. uMCP-1 is most likely generated locally in the kidney.