We aimed to characterize the salivary protein components and identify biomarkers in patients with systemic lupus erythematosus (SLE). A proteomic analysis using two-dimensional gel electrophoresis and mass spectrometry was performed to determine the alterations of salivary proteins between patients with SLE and healthy controls, and the concentrations of the candidate proteins were measured through Western blot analysis and the enzyme-linked immunosorbent assay. The 10 differentially expressed protein spots were immunoglobulin gamma-3 chain C region (IGHG3), immunoglobulin alpha-1 chain C region, protein S100A8, lactoferrin, leukemia-associated protein 7, and 8-oxoguanine DNA glycosylase. The patients with SLE exhibited enhanced salivary IGHG3 (3.9 ± 2.15 pg/mL) and lactoferrin (4.7 ± 1.8 pg/mL) levels compared to patients with rheumatoid arthritis (1.8 ± 1.01 pg/mL and 3.2 ± 1.6 pg/mL, respectively; p < 0.001 for both) or healthy controls (2.2 ± 1.64 pg/mL and 2.2 ± 1.7 pg/mL, respectively; p < 0.001 for both). The salivary IGHG3 levels correlated with the erythrocyte sedimentation rate (r = 0.26, p = 0.01), anti-double-stranded DNA (dsDNA) antibody levels (r = 0.25, p = 0.01), and nephritis (r = 0.28, p = 0.01). The proteomic analysis revealed that the salivary IGHG3 levels were associated with SLE and lupus disease activity, suggesting that salivary IGHG3 may be a promising noninvasive biomarker for SLE.

Background Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies and systemic inflammatory response. We aimed to characterize the salivary protein components and find biomarkers in patients with SLE. Methods The pooled salivary proteins of patients with SLE and healthy controls were subjected to 2-dimensional gel electrophoresis. The spots exhibiting > 2-fold intensity change between SLE and healthy controls were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis. Results The proteomic analysis using 2-dimensional gel electrophoresis and mass spectrometry revealed 10 differentially expressed protein spots, which included immunoglobulin gamma-3 chain C region (IGHG3), immunoglobulin alpha-1 chain C region (IGHA1), protein S100, lactoferrin, leukemia-associated protein 7, and 8-oxoguanine deoxyribonucleic acid glycosylase. The patients with SLE exhibited enhanced salivary IGHG3 (3.9 ± 2.15 pg/mL) and lactoferrin (4.7 ± 1.8 pg/mL) levels than patients with rheumatoid arthritis (1.8 ± 1.01 pg/mL and 3.2 ± 1.6 pg/mL, respectively, p < 0.001 for both) or healthy controls (2.2 ± 1.64 pg/mL and 2.2 ± 1.7 pg/mL, respectively, p < 0.001 for both). The salivary IGHG3 levels correlated with erythrocyte sedimentation rate (r = 0.26, p = 0.01), anti-double-strand deoxyribonucleic acid antibody levels (r = 0.25, p = 0.01), and nephritis (r = 0.28, p = 0.01). Conclusions Patients with SLE exhibited elevated salivary IGHG3 and lactoferrin levels, and the salivary IGHG3 levels correlated with disease activity markers of SLE. Salivary IGHG3 may be a promising non-invasive biomarker in SLE.