**Core Concept**
The question tests the student's understanding of the pathophysiology of inflammation, specifically the mediators involved in the chemotaxis of inflammatory cells to the site of infection. In this case, the patient has a respiratory infection caused by Gram-positive diplococci, which triggers an inflammatory response in the lungs.

**Why the Correct Answer is Right**
N-formylated peptides are potent chemotactic factors that attract neutrophils to the site of infection. These peptides are produced by the bacterial cell wall and are recognized by specific receptors on the surface of neutrophils. Upon binding to these receptors, neutrophils undergo a conformational change that activates their chemotactic machinery, allowing them to migrate towards the source of the signal (in this case, the alveolar air spaces). The directed migration of neutrophils is crucial for the elimination of the bacterial infection.

**Why Each Wrong Option is Incorrect**
**Option A:** Bradykinin is a potent vasodilator and a mediator of pain and inflammation, but it is not a chemotactic factor for inflammatory cells.
**Option B:** Histamine is a mediator of allergic reactions and inflammation, but it is not a chemotactic factor for neutrophils.
**Option C:** Myeloperoxidase is an enzyme found in neutrophils that plays a role in the killing of bacteria, but it is not a chemotactic factor.

**Clinical Pearl / High-Yield Fact**
N-formylated peptides are a class of chemotactic factors that are recognized by specific receptors on the surface of neutrophils. This recognition process is a critical step in the recruitment of neutrophils to the site of infection, and it is an important area of research in the development of new antimicrobial therapies.

**✓ Correct Answer: D. N-formylated peptides**