Which innate immune cells are among the first responders to bacterial infection?

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

Answer: (A)

Neutrophils are the first responders to bacterial infection. They’re the most abundant white blood cells and are released quickly from the bone marrow in response to inflammatory signals at the infection site. They rush to the area through chemotaxis, engulf invading bacteria (phagocytosis), and kill them using reactive oxygen species and granule enzymes. Their rapid arrival and action make them the immediate frontline defense in bacterial infections.

Lymphocytes are part of the adaptive immune system and require antigen-specific activation, so they take longer to become effective against bacteria. Eosinophils mainly combat parasites and are more involved in allergic responses, not the initial bacterial assault. Monocytes arrive after neutrophils and differentiate into macrophages that continue phagocytosis and help with antigen presentation, but they come later in the response.