Conformational activation of CD11b without shedding of L-selectin on circulating human neutrophils.
Membrane-activated complex 1 (Mac-1; CD11b/CD18) is a beta(2) 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<0.0001) peri-operatively, whereas total CD11b expression increased only transiently, intra-operatively. L-selectin expression was unchanged on CBRM1/5+ neutrophils, and soluble L-selectin levels decreased intra-operatively (P<0.01), indicating that L-selectin was not shed. Increased CBRM1/5 expression without L-selectin loss or CD11b up-regulation was replicated in vitro by neutrophil stimulation with IL-8, C3a, and platelet-activating factor. Heparin, a known CD11b ligand, which is administered during cardiac surgery, markedly reduced neutrophil expression of conformationally active CD11b in vivo and in vitro, identifying a potential mechanism for its anti-inflammatory properties. We conclude that conformational activation of CD11b occurs on circulating neutrophils in vivo and can occur in the absence of CD11b up-regulation and L-selectin shedding.
Centre for Vascular Research, School of Medical Sciences, 4th Floor Wallace Wurth Building, The University of New South Wales, Kensington, NSW, Australia.
Y
Y
Orr
J M
JM
Taylor
S
S
Cartland
P G
PG
Bannon
C
C
Geczy
L
L
Kritharides
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000787:Angina Pectoris / Q000276:immunology / Q000378:metabolism* / Q000601:surgery; D039481:CD11b Antigen / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002908:Chronic Disease; D015926:Complement C3a / Q000378:metabolism; D001026:Coronary Artery Bypass; D000939:Epitopes / Q000276:immunology / Q000378:metabolism; D005260:Female; D005434:Flow Cytometry; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D019041:L-Selectin / Q000378:metabolism*; D016177:Macrophage-1 Antigen / Q000276:immunology* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D018375:Neutrophil Activation; D009504:Neutrophils / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000378:metabolism; D011446:Prospective Studies; D011487:Protein Conformation; D015398:Signal Transduction
D039481:CD11b Antigen; D000939:Epitopes; C509295:ITGAM protein, human; D016209:Interleukin-8; D016177:Macrophage-1 Antigen; D010972:Platelet Activating Factor; D019041:L-Selectin; D015926:Complement C3a; D006493:Heparin