What types of leukocytes are involved in the immune response?

• A. B lymphocytes, T lymphocytes, granulocytes (eosinophils, basophils, neutrophils), and monocytes.
• B. Red blood cells and platelets.
• C. Platelets only.
• D. Muscle cells and adipocytes.

Answer: (A)

Leukocytes are the white blood cells that drive immune defense, spanning both immediate innate responses and targeted adaptive responses. B lymphocytes and T lymphocytes are the adaptive component: B cells produce antibodies to tag pathogens, while T cells coordinate and execute responses against infected or abnormal cells. Granulocytes—neutrophils, eosinophils, and basophils—are rapid innate responders: neutrophils rush in to phagocytose microbes, eosinophils combat parasites and participate in allergic reactions, and basophils release mediators that promote inflammation. Monocytes circulating in blood can differentiate into macrophages and dendritic cells, which engulf pathogens and present antigens to T cells, helping to activate the adaptive response. Together, these leukocyte types illustrate the main players in the immune response. Red blood cells and platelets are not leukocytes, though platelets participate in clotting and can influence inflammation; muscle cells and adipocytes are not immune cells.