Final answer:
Eosinophils are eosinophilic leukocytes that help defend against parasites and counteract histamines. They also participate in phagocytosis and can be elevated in certain conditions.
Step-by-step explanation:
Eosinophils are eosinophilic leukocytes that play a role in the immune response, particularly in defending against parasites. They contain granules that release antihistamine molecules to counteract the activities of histamines produced by basophils and mast cells. Eosinophils are also involved in phagocytosis and can be elevated in patients with allergies, parasitic worm infestations, and autoimmune diseases.