Review Question - QID 106267

A 4-year-old male is brought to the office by his mother with a 4-day history of nose bleeds and bleeding gums. The patient has no past medical history and does not take medications. He denies any similar past episodes, as well as oliguria, bloody stools, headache, or diarrhea. His vitals signs are as follows: 37C, BP92/60, HR82, RR18. The patient is fully alert and oriented. Physical examination is notable for diffuse petechial rash on the bilateral lower extremities. Complete blood count reveals a platelet count of 20,000 per mm^3. A bone marrow aspiration smear is seen in Figure A and the pathologist notes an increased number of the large cells in other fields. Which of the following is the most likely mechanism underlying the patient's illness?