demargination

Demargination is the physiological process by which leukocytes, predominantly neutrophils, detach from the endothelium-adhered marginated pool in the microcirculation and re-enter the circulating blood volume. A marginated pool exists along the walls of small vessels—especially in the lungs, liver, spleen, and bone marrow microvasculature—where neutrophils temporarily adhere before they can rejoin the circulating pool or migrate into tissues.

Demargination can occur rapidly, typically within minutes, and is largely driven by sympathetic activation that releases catecholamines such as epinephrine, reducing the sticking of neutrophils to the endothelium. Glucocorticoids and certain other stimuli can also promote demargination by mobilizing marginated cells. The process increases the number of leukocytes detected in peripheral blood without changes in marrow production and is most apparent for neutrophils; other leukocytes may participate to a lesser extent.

Demargination is distinct from diapedesis, the active migration of leukocytes through the endothelium into tissues during inflammation. The marginated pool can be replenished from circulating neutrophils and bone marrow, and levels typically normalize after the acute stimulus subsides.

Clinical significance: Demargination contributes to transient leukocytosis in response to stress, exercise, anesthesia, and some pharmacologic therapies, and can confound interpretation of WBC counts in such contexts. It also illustrates the dynamic distribution of immune cells between vascular and tissue compartments.