What is the least common of the WBC's?

The basophil is considered the least common type of white blood cell (WBC) in the human body, making it the correct answer in this context. Basophils typically make up less than 1% of the total white blood cell count. These cells play a crucial role in inflammatory responses, especially during allergic reactions, by releasing histamine and other chemicals.

The other white blood cells mentioned have higher prevalence levels in the blood. Neutrophils are the most abundant, accounting for approximately 50-70% of the WBC count, indicating their primary role in fighting off infections, particularly bacterial ones. Lymphocytes, which are also more prevalent, represent about 20-40% of the total WBC count and are essential for the immune response. Eosinophils are less common than neutrophils and lymphocytes but still have a higher percentage than basophils, making up about 1-4% of WBCs and functioning mainly in combating parasites and being involved in allergic reactions.

In summary, the role of basophils, their contribution to immunity and inflammation, along with their low abundance in circulation, clearly identifies them as the least common type of white blood cell.