Which white blood cell is typically the earliest responder to infection due to its phagocytic activity?

• A. Lymphocytes
• B. Monocytes
• C. Eosinophils
• D. Neutrophils

Answer: (D)

Early in an infection, the body relies on innate defenses, and neutrophils are the first to respond. They are the most abundant white blood cells and are specialized for rapid phagocytosis. Neutrophils are quickly recruited to the infection site by chemical signals, where they engulf and destroy invading microbes and release enzymes and reactive species to kill what they ingest. This rapid, high-volume response makes them the typical earliest attackers in acute infections, especially bacterial ones. Lymphocytes belong to adaptive immunity and take longer to activate after antigen exposure. Monocytes also perform phagocytosis, but they arrive after neutrophils and differentiate into macrophages in tissues. Eosinophils focus on parasites and play roles in allergies rather than the immediate bacterial clearance typical of the initial response.