Abstract
Hepatic neutrophil adhesion during endotoxemia is an integrin-independent, CD44-dependent process. Because integrins function in other endotoxemic vasculatures, we used spinning disk confocal intravital microscopy to assess whether LPS down-modulated integrin functions in sinusoids. First, we applied fMLP onto the liver surface, and compared it with systemic LPS administration. Local fMLP caused neutrophil adhesion, crawling, and emigration for at least 2 h. Surprisingly, the number of adherent and crawling neutrophils was markedly reduced in Mac-1−/− and ICAM-1−/− mice, but not in mice treated with anti-CD44 mAb. By contrast, systemic LPS injection induced a robust accumulation of neutrophils in sinusoids, which was dependent on CD44, but not on integrins. Strikingly, local fMLP could not induce any integrin-dependent adhesion in endotoxemic mice treated with anti-CD44 mAb, indicating that Mac-1-dependent neutrophil adhesion was inhibited by LPS. This response was localized to the hepatic microvasculature because neutrophils still adhered via integrins in brain microvasculature. ICAM-1/ICAM-2 levels were not decreased, but following LPS treatment, Mac-1 was down-regulated in neutrophils localized to liver, but not in the circulation. Mac-1 down-regulation in neutrophils was not observed in IL-10−/− mice. In vitro neutrophil incubation with IL-10 induced direct decrease of Mac-1 expression and adhesivity in LPS-stimulated neutrophils. Therefore, our data suggest that Mac-1 is necessary for neutrophil adhesion and crawling during local inflammatory stimuli in sinusoids, but during systemic inflammation, neutrophils are exposed to high concentrations of IL-10, leading to a CD44-dependent, integrin-independent adhesion. This may be a mechanism to keep neutrophils in sinusoids for intravascular trapping.
Footnotes
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↵1 This work was supported by Canadian Institutes for Health Research operating grant and grant group. G.B.M. received a fellowship from Fundação de Amparo a Pesquisa de Minas Gerais, Brazil. C.M.W. is founded by a RE/MAX Fellowship through the Alberta Children’s Hospital Foundation, and is a Canadian Institutes for Health Research Training Fellow in the Canadian Child Health Clinician Scientist Program, in partnership with SickKids Foundation and the Child and Family Research Institute of British Columbia. D.C.C. is a Conselho Nacional do Desenvolvimento Científico e Tecnológico (Conselho Nacional de Pesquisas) Scientist. P.K. is an Alberta Heritage Foundation for Medical Research Scientist and the Snyder Chair in Critical Care Medicine.
↵2 Address correspondence and reprint requests to Dr. Paul Kubes, Calvin, Phoebe and Joan Snyder Institute for Infection, Immunity and Inflammation, HRIC 4A26A, University of Calgary 3280 Hospital Drive N.W., Calgary, Alberta, T2N 4N1 Canada. E-mail address: pkubes{at}ucalgary.ca
- Received June 5, 2009.
- Accepted October 4, 2009.
- Copyright © 2009 by The American Association of Immunologists, Inc.