Which white blood cell is primarily involved in defense against parasites and in allergic responses?

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

Answer: (B)

Eosinophils are the white blood cells specialized for defense against parasites and for modulating allergic inflammation. They circulate and migrate to areas where parasites are present, releasing granule contents such as major basic protein that directly damage helminths and other parasites. They also participate in antibody-dependent cellular cytotoxicity by recognizing IgE-coated targets, helping to kill parasites that antibodies have marked. In allergic settings, eosinophils amplify and shape the inflammatory response, contributing to symptoms in conditions like asthma and allergic rhinitis. Their development and activation are driven by interleukin-5 from Th2 cells, aligning them with both parasite defense and allergy. By contrast, B lymphocytes mainly produce antibodies, neutrophils are the primary first responders to bacterial infections, and basophils promote allergic inflammation but are not primarily involved in parasite defense.