Final answer:
Eosinophils are a type of white blood cell that targets parasitic infections and is involved in allergic responses. They increase in number during allergies and helminth infections and can bind to parasites tagged by IgE antibodies to attack them. The correct option is D)
Step-by-step explanation:
The student's question is focused on eosinophils, which are a type of white blood cell (leukocyte) primarily involved in the body's immune response to parasites and allergens. Eosinophils are known for their role in the immune defense against parasitic infections by helminths (parasitic worms) and also play a part in allergic reactions due to their ability to release inflammatory substances like histamine. They are attracted to the site of infection or infestation by chemotactic signals such as cytokines released by T cells and upon arrival, they release granule contents that can combat pathogens. In case of allergic reactions or helminth infections, there is typically an increase in the number of eosinophils. Furthermore, during a parasitic infection, if an IgE antibody labels the parasite, eosinophils are able to bind to it via their Fc receptor and contribute to the immune response.