A 60-year-old woman presents with swelling of both hands and feet for 3 years. Blood pressure (BP) 180/130 mmHg, facial skin without wrinkles, perioral furrows. Urinary protein (++) (1.9g/d), urinary red blood cells (RBCs) 25-30/HPF, hemoglobin (Hb) 100g/L, blood urea nitrogen (BUN) 20.8 mmol/L, antinuclear antibody (ANA) positive. Which immunological marker is most helpful for diagnosis?