Final answer:
Basophils make up less than 1% of the total leukocyte count in healthy adults, are the least common leukocytes, and secrete chemicals like histamine and heparin that aid in the body's immune response.
Step-by-step explanation:
In a healthy adult, basophils constitute about <1% of the total leukocyte count. Basophils are the least common type of white blood cells, with their numbers being significantly lower than other leukocytes such as neutrophils, eosinophils, and lymphocytes.
Being slightly smaller than neutrophils and eosinophils, basophils are recognized by their large granules that stain a dark blue with basic (alkaline) stains, sometimes obscuring the view of their two-lobed nucleus. Histamine and heparin are the chemicals secreted by basophils, playing an essential role in body defenses such as increasing vasodilation and permeability during inflammation and preventing blood clotting, respectively.