Which blood component fights infection?

• A. white blood cells
• B. red blood cells
• C. platelets
• D. plasma

Answer: (A)

White blood cells are the main defenders against infection. They roam the bloodstream and tissues, recognize invading pathogens, and actively attack them through processes like phagocytosis (engulfing and destroying microbes) and by coordinating the immune response. Some white blood cells, such as B cells, also produce antibodies that help target pathogens, but the actual fighting force comes from the white blood cells themselves. Red blood cells carry oxygen, not infection defense; platelets aid in clotting and wound repair; plasma is the fluid that transports cells and proteins (including antibodies), but it’s the white blood cells that actively combat infection.