Conformational activation of CD11b without shedding of L-selectin on circulating human neutrophils

Membrane‐activated complex 1 (Mac‐1; CD11b/CD18) is a β2 integrin implicated in the pathophysiology of neutrophil‐mediated tissue injury whose functional capacity is determined by stimulus‐induced conformational activation rather than up‐regulation. Mac‐1 up‐regulation and conformational activation, together with shedding of L‐selectin, are reported after in vitro neutrophil activation. However, their regulation on circulating human neutrophils during acute inflammation is unclear. Using flow cytometry, we investigated neutrophil expression of Mac‐1, its activation‐reporter neo‐epitope CBRM1/5, and L‐selectin during the inflammatory stimulus of cardiac surgery. A subpopulation of circulating neutrophils expressed CBRM1/5 (CBRM1/5+) under basal conditions (6.28±2.59%) and was persistently expanded (9.95±4.0%–15.2±4.2%; P