Q. A 34-year-old woman comes to the emergency department because of a fever. The patient has no medical history and currently takes no medications. She frequently applies sunscreen, as her face burns easily. She does not smoke or drink alcohol. Vital signs are normal except for a low-grade fever. Upon examination, a facial rash is noted sparing the nasolabial fold with multiple associated oral ulcers. Cardiac auscultation reveals a holosystolic murmur in the mitral area. The patient's lab results show thrombocytopenia with elevation in the antinuclear antibody titer. Which of the following is the most likely cause of this patient's cardiac findings?