Increased serum, salivary, and urinary immunoglobulin gamma-3 chain C levels are observed in systemic lupus erythematosus patients.
Immunoglobulin gamma-3 chain C (IGHG3) is a type of IgG that plays a major role in the pathogenesis of systemic lupus erythematosus (SLE). It contributes to hypergammaglobulinemia and IgG immune complex deposition in tissues, leading to organ damage in these patients. Its distribution and role in the different bodily fluids and tissues have not been extensively studied. A study published in the International Journal of Molecular Sciences assessed the clinical value of IGHG3 by measuring and comparing its levels in different bodily fluids of SLE patients.
In total, 181 SLE patients and 99 healthy controls (HCs) were enrolled in the study. The mean age of SLE patients was approximately 38.8, 38.9, and 41.1 years, and the mean disease duration was 6.6, 6.9, and 7.89 years in the saliva, serum, and urine groups, respectively. Anti-double stranded(ds)DNA antibody positivity was 36.7%, 41.0%, and 38.2%, respectively. Among SLE patients 41.4%, 44%, and 30.6% had arthritis; 17.8%, 19.4%, and 21.0% had active lupus nephritis; and 21.2%, 26.1%, and 14.0% had hematologic involvement in the saliva, serum, and urine groups, respectively. The mean systemic lupus erythematosus disease activity index (SLEDAI) score was approximately 3.9, 4.3, and 4.1 in the saliva, serum, and urine groups, respectively.
Comparison of Healthy Controls and SLE Samples for IGHG3
Serum, salivary, and urinary IGHG3 levels were significantly higher in SLE patients than HCs (p < 0.001).
ROC Curve of IGHG3 Levels for Distinguishing SLE
Comparing the receiver operating characteristic (ROC) curves identified that the area under the curve (AUC) of IGHG3 for serum better distinguished SLE than that for saliva and urine.
Association of IGHG3 Levels With Clinical Markers in SLE
The salivary IGHG3 levels were positively correlated with the erythrocyte sedimentation rate. Serum IGHG3 levels were negatively correlated with leukocyte count, lymphocyte count, and C3 concentrations and positively correlated with anti-dsDNA positivity.
Urinary levels of IGHG3 positively correlated with the ESR, SLEDAI-2K score, and anti-dsDNA positivity and negatively correlated with hemoglobin and C3, indicating that higher urinary IgG3 levels suggest an active status of SLE or lupus nephritis.
Association of IGHG3 Levels With Specific Disease Manifestations
Urinary IGHG3 levels showed significant efficacy in distinguishing active lupus nephritis, as levels were significantly higher in these patients and those with SLEDAI-2K > 6. Salivary IGHG3 levels were similar regardless of the presence or absence of specific SLE manifestations. Serum IGHG3 levels were significantly lower in febrile patients.
Jung, J., Kim, J., Lee, S., Baek, W., Kim, H., & Suh, C. (2023). Increased Immunoglobulin Gamma-3 Chain C in the Serum, Saliva, and Urine of Patients with Systemic Lupus Erythematosus. International Journal of Molecular Sciences, 24(8), 6927. https://doi.org/10.3390/ijms24086927