Question: A 28 year old male is referred to you for recurrent epistaxis. Examination reveals extensive nasal crusting, an ulcerated septal perforation, and no telangiectasias. Biopsy of the perforation reveals active vasculitis and a diagnosis of GPA is suspected. What is the antigenic target within the cytoplasm in c-ANCA positive GPA?

[Answer will be posted with next week's new question]

Answer to last week's question, "Shredded Cables" (December 18, 2017)