Which white blood cell is most associated with killing parasites and helminths and is phagocytic?

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

Answer: (C)

Defending against parasites, especially helminths, relies on a cell type that can target large, multicellular invaders and damage them directly. Eosinophils fit this role best. They are drawn to sites of parasitic infection and, when activated, release potent cytotoxic granules—such as major basic protein and eosinophil peroxidase—that disrupt the parasite’s surface. They can kill parasites through these granule contents and by antibody-dependent mechanisms when parasites are coated with IgE. Eosinophils are also capable of phagocytosis of small particles and immune complexes, but their specialized weaponry and recruitment to parasite infections make them the standout cells for fighting helminths. In contrast, neutrophils are the primary bacteria-fighting phagocytes, monocytes/macrophages handle a broad range of pathogens, and basophils mainly drive allergic responses, so they aren’t as closely linked to parasite killing.