An endoscopy is performed on a 28-year-old man with a 3-year history of crampy right lower quadrant pain, chronic diarrhea, and weight loss. The endoscopic findings shown in the diagram at **A** reveal skip lesions, aphthous ulcers, deep linear ulcers, and cobblestone mucosa with rectal sparing. The terminal ileum is intubated and shows similar changes. Which of the following BEST explains the pathogenesis of the mucosal inflammation pattern observed at **A**?