[The effects of S100A9 gene knockout on lupus-like phenotype in mice]

Objective To explore the effects of S100 calcium-binding protein A9 (S100A9) gene knockout on the phenotype of systemic lupus erythematosus (SLE) in mice and to clarify the role of S100A9 in the pathogenesis of SLE. Methods Ten female C57BL/6 wild-type and S100A9 knockout (S100A9-KO ) mice were selected, with five wild-type and five S100A9-KO B6 mice receiving imiquimod (IMQ) cream to establish SLE mouse model. The other five wild-type and five S100A9-KO B6 mice were treated as control groups by wiping the skin of the right ear with a cotton swab. After 8 weeks, the mice were sacrificed. The serum was collected from each mouse to detect the levels of anti-double-stranded DNA (dsDNA) antibodies, immunoglobulin G (IgG), B cell activating factor (BAFF), and interleukin 6 (IL-6) using ELISA. The levels of serum creatinine were determined using a sarcosine oxidase method. Urine was collected to measure urinary protein concentration. Kidneys were collected and stained with hematoxylin and eosin (H&E) for evaluating histological changes. Results After IMQ treatment, the length and weight of spleen, levels of serum creatinine, anti-dsDNA antibodies, IgG, BAFF, IL-6, and urinary protein in the IMQ B6 group and IMQ S100A9-KO B6 group were significantly higher than those of the control groups. Lupus-like changes including increased glomerular volume and tubular epithelial swelling were observed in kidneys from the IMQ and IMQ S100A9-KO groups. However, compared with the IMQ B6 group, the IMQ S100A9-KO B6 group exhibited milder levels of serum and urine indicators as well as the lupus-like symptoms. Conclusion IMQ could induce lupus-like symptoms in both wild-type B6 mice and S100A9-KO B6 mice, but the lesions in S100A9 knockout mice are milder. Theses results suggested that S100A9 is involved in and promotes the pathogenesis of SLE.