Which immune cells are the first responders during an acute bacterial infection?

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

Answer: (C)

The first immune responders to an acute bacterial infection are neutrophils. These abundant white blood cells rapidly leave the bloodstream and migrate to the site of infection in response to chemical signals released by bacteria and damaged tissue. Once there, they quickly engulf and kill bacteria through phagocytosis and the production of reactive oxygen species and enzymes, acting as the immediate frontline defense. Their short lifespan and rapid turnover allow the body to mount a quick, initial containment of the invading bacteria, which is why you often see signs of an acute bacterial infection accompanied by a neutrophil-driven response (sometimes with more immature neutrophils appearing as a left shift). Lymphocytes are part of the adaptive immune response and take longer to activate, so they aren’t the first responders. Eosinophils and basophils are involved more with parasites, allergies, and inflammatory signaling, not the immediate bacterial attack.