Review Question - QID 108946

A 45-year-old male presents to his primary care physician complaining of joint pain and stiffness. He reports progressively worsening pain and stiffness in his wrists and fingers bilaterally over the past six months that appears to improve in the afternoon and evening. His past medical history is notable for obesity and diabetes mellitus. He takes metformin and glyburide. His family history is notable for osteoarthritis in his father and psoriasis in his mother. His temperature is 98.6°F (37°C), blood pressure is 130/80 mmHg, pulse is 90/min, and respirations are 16/min. On examination, his bilateral metacarpophalangeal joints and proximal interphalangeal joints are warm and mildly edematous. The presence of antibodies directed against which of the following is most specific for this patient’s condition?