A 32-year-old woman presents to the emergency department with severe right lower abdominal pain, fever (38.5°C), and vomiting for 8 hours. On examination, she has rebound tenderness and guarding in the right iliac fossa. Ultrasound shows a dilated, non-compressible appendix with echogenic material inside and free fluid in the pelvis. Blood work reveals WBC 14,500/μL with left shift, and CRP 8.2 mg/dL. She is taken to the operating theatre for an emergency appendectomy. Histopathology of the resected appendix shows transmural infiltration by neutrophils, fibrin deposition, ulceration of the mucosa, and early abscess formation. Which of the following best describes the predominant cellular event occurring in the appendiceal wall at this stage of acute inflammation?