Which type of leukocyte is most abundant in the bloodstream?

Neutrophils are the most abundant type of leukocytes, commonly making up about 55% to 70% of the white blood cells in a healthy adult's bloodstream. They play a crucial role in the immune response by providing the first line of defense against infections, particularly bacterial infections. Neutrophils are characterized by their ability to quickly respond to sites of inflammation or infection, where they engulf and destroy pathogens. Their high abundance reflects their vital role in maintaining the body's defense mechanisms.

In contrast, lymphocytes, basophils, and eosinophils have lesser populations in the bloodstream. Lymphocytes are instrumental in adaptive immunity, including the production of antibodies, while basophils and eosinophils are primarily involved in allergic responses and combating parasitic infections, respectively. Their relative scarcity compared to neutrophils underlines the specialized roles these other leukocytes play in the immune system rather than the frontline response of neutrophils.