Which white blood cell is primarily involved in parasitic infections and allergic reactions and is not primarily phagocytic?

• A. Neutrophil
• B. Eosinophil
• C. Basophil
• D. Lymphocyte

Answer: (B)

Specialized roles of white blood cells matter: eosinophils are set apart for defense against parasites and involvement in allergic reactions, and they are not primarily phagocytic. When parasites are too large to be engulfed, eosinophils release cytotoxic granules containing proteins like major basic protein and eosinophil cationic protein to damage and kill the invaders. They also participate in allergic inflammation, often in response to IgE and Th2 cytokines such as IL-5, helping modulate the immune response in allergies. Neutrophils are the main phagocytes handling bacteria and acute bacterial infections, so phagocytosis is their forte. Basophils contribute to allergic responses by releasing histamine and other mediators, but their primary role isn’t parasite defense. Lymphocytes are primarily involved in adaptive immunity (antibody production, T-cell–mediated responses) rather than direct phagocytosis. Therefore, the cell best matching parasitic defense and allergy involvement without being a primary phagocyte is the eosinophil.