You are answering a USMLE-style medical question. Question: A patient with a1-antitrypsin deficiency is warned by his physician that his increasing dyspnea may be worsened by his continued cigarette smoking. Which of the following factors, released by both neutrophils and alveolar macrophages, is responsible for the patient's condition? Options: A) Major Basic Protein B) Mucus C) Surfactant D) Elastase Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.