C3 and systemic lupus erythematosus: HC: Healthy Control; non-NPSLE: Non-neuropsychiatric Systemic Lupus Erythematosus; SLEDAI: Systemic Lupus Erythematosus Disease Activity Index; SDI: Systemic Lupus International Collaborating Clinics /American College of Rheumatology (SLICC/ACR) Damage Index; Serology: C3, C4 and CH50.