Review Question - QID 108948

A 17-year-old male presents to the pediatrician complaining of malaise. He reports a three-day history of fatigue, painful joints, a skin rash, and fevers. He was recently seen by his pediatrician for a sore throat of presumed viral etiology. His past medical history is notable for severe mononucleosis one year ago and poorly controlled asthma. He currently takes inhaled salmeterol and fluticasone. His temperature is 101.0°F (38.3°C), blood pressure is 120/70 mmHg, pulse is 110/min, and respirations are 20/min. Range of motion is full in the bilateral upper and lower extremities; however, the patient reports mild pain in his elbow and knees. A notable physical examination finding is shown in Figure A. Antibodies directed against a protein with which of the following functions are most likely responsible for this patient’s condition?