C3 and systemic lupus erythematosus: The decrease of serum C3 and C4 in this patient was related to the complement consumption caused by complement system activation, and the activated C3 and C4 are involved in the inflammatory reaction, which can induce autoantibodies to form immune complexes with their antigens and deposit in organs and tissues, resulting in damage to tissues and organs.[16] In this case, SLE involvement in the blood system and kidneys is the cause of hemocyte depletion and renal dysfunction.