The differential count estimates the number of the various types of WBCs and is used to differentiate the type of response in progress. B-type lymphocytes synthesize and secrete antibodies . Cytotoxic T lymphocytes recognize and destroy virus-infected cells.
Monocytes recognize a variety of microorganisms, especially gram-negative bacteria.
Activated monocytes turn into macrophages that can engulf and destroy microorganisms and secrete a variety of cytokines that modulate the activity of other leukocytes. Eosinophils and basophils release substances that cause vasoconstriction , smooth muscle contraction , and an increased permeability of small blood vessels. Eosinophils are stimulated by parasites and some bacteria. Basophils are stimulated by allergens. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe.