Which is the least common type of white blood cell in the body?

• A. Neutrophils
• B. Lymphocytes
• C. Monocytes
• D. Basophils

Answer: (D)

The main idea is how white blood cell types are distributed in normal blood. Neutrophils are the most abundant, acting as first responders to bacterial infection. Lymphocytes, including T and B cells, are the next most common and are central to adaptive immunity. Monocytes are less numerous than lymphocytes and neutrophils, and they become macrophages in tissues. Basophils are the least common type, usually making up well under 1% of circulating white blood cells. Their granules contain histamine and heparin and they mainly contribute to allergic reactions and certain inflammatory responses. Because they occur in such small numbers under normal conditions, basophils are the least frequent.