Purpose The possibility of exploring other body fluids to identify potential biomarkers of systemic inflammation has emerged as a non-invasive alternative to blood samples for both diagnosis and control of disease activity. We investigated the levels of innate-immunity related biomarkers in saliva, serum, and urine from Systemic Lupus Erythematous (SLE) patients and their correlation to each other and to disease activity.

Methods We included 84 SLE patients and 20 controls from the general population, all participants underwent a thorough clinical examination. Disease activity as measured with the Systemic Lupus Activity Measure (SLAM) and SLE Disease Activity Index-2K(SLEDAI-2K) was recorded. Matched saliva, serum, and urine were collected, and the levels of colony-stimulating factor (CSF)-1, tumor necrosis factor (TNF)-α, interferon-γ-induced protein (IP)-10, monocyte chemoattractant protein (MCP)-1 and calprotectin were analysed by enzyme-linked immunosorbent assays (ELISA) and Bead-based Multiplex immunoassay.

Results TNF-α, IP-10 and MCP-1 in saliva, serum and urine, and CSF-1 in saliva and serum provided diagnostic ability to distinguish SLE from controls (area under the curve >0.659, p<0.05 for all). CSF-1, TNF-α, IP-10 and MCP-1 in saliva, serum and urine as well as calprotectin in saliva and urine were increased in SLE patients. Levels of CSF-1 in saliva, serum and urine, IP-10 in serum and urine, and calprotectin in saliva and urine, as well as TNF-α, IP-10 and MCP-1 in urine correlated positively with measures of disease activity. TNF-α, IP-10 and MCP-1 in urine and CSF-1 and IP-10 in serum were elevated in patients with active renal disease (p<0.05 all comparisons).

Conclusion The proposed biomarkers provide diagnostic ability to distinguish SLE from controls and they also reflect disease activity. This is a promising result suggesting that in some situations either saliva or urine samples might be capable to be an alternative to serum when diagnosing and monitoring patients with SLE.