Given the lack of improvement of antibiotics, an immunological workup for SLE was initiated, which showed low CH50, C3, and C4; anti-nucleic acid antibody (ANA) was 1:1280, anti-double-stranded (anti-DS) DNA antibody not detected, and fluorescent ANA was positive. For severe NPSLE, rituximab is the most commonly utilized immunosuppressant; it was not utilized in this case due to the patient's insurance. This evidence concerns the gene C3 and systemic lupus erythematosus.