Which immune cell is primarily responsible for phagocytosis in the early response to bacterial infections?

• A. Erythrocytes
• B. Platelets
• C. Neutrophils
• D. B cells

Answer: (C)

Neutrophils are the first line of defense in bacterial infections, acting as professional phagocytes that respond rapidly to sites of infection. They’re recruited from the blood by chemotactic signals (like IL-8 and C5a), arrive quickly, and engulf bacteria into a phagosome. The phagosome then fuses with granules containing reactive oxygen species and enzymes, producing a rapid kill of the invader. This rapid, non-specific phagocytosis is what characterizes the early innate response.

Erythrocytes don’t participate in immune defense. Platelets mainly help with clotting and can assist inflammation, but they aren’t the primary cells for phagocytosis. B cells are part of the adaptive immune response and produce antibodies; they don’t perform the initial engulfing of bacteria. Thus, neutrophils best fit the role described in the question.