Which blood component is primarily involved in the immune response?

• A. White blood cells
• B. Red blood cells
• C. Platelets
• D. Plasma

Answer: (A)

White blood cells are the immune system’s frontline in the blood. They circulate through the body, detect foreign invaders, and actively defend against them. Some white blood cells, like neutrophils and macrophages, engulf pathogens through phagocytosis, while others, such as lymphocytes, provide targeted, adaptive immunity by producing antibodies (B cells) and destroying infected cells (T cells). Red blood cells carry oxygen and carbon dioxide and don’t fight infections. Platelets help with clotting, not defense against pathogens. Plasma is the fluid that carries cells and proteins, including antibodies, but the direct immune actions come from the white blood cells. That’s why white blood cells are the component primarily involved in the immune response.