Syk Is Downstream of Intercellular Adhesion Molecule-1 and Mediates Human Rhinovirus Activation of p38 MAPK in Airway Epithelial Cells

To evaluate the factors controlling migration of leukocytes into pulmonary airway epithelium, we determined the biochemical mechanisms responsible for the regulation of intercellular adhesion molecule-1 (ICAM-1) expression on cultured monolayers of human tracheal epithelial cells (HTECs) or SV40 virus-transformed human bronchial epithelial cells (BEAS-2B). Validation experiments with human umbilical vein endothelial cells (HUVECs) demonstrated little detectable ICAM-1 expression on unstimulated cells or on cells incubated with interferon-gamma (IFN-gamma), but HUVEC monolayers responded to interleukin-1 beta (IL-1 beta) or tumor necrosis factor-alpha (TNF-alpha) with significant increases in ICAM-1 and ICAM-1-dependent adherence of polymorphonuclear leukocytes (PMNs). HTEC monolayers also exhibited no significant basal ICAM-1 expression but, in contrast to HUVEC monolayers, had marked increases in ICAM-1 expression and ICAM-1-dependent PMN adherence only after incubation with IFN-gamma (and not after IL-1 beta or TNF-alpha) treatment. BEAS-2B cells also exhibited relatively selective IFN-gamma stimulation of ICAM-1 expression and ICAM-1-dependent PMN adherence but (like late passage HTEC) showed significant basal ICAM-1 expression. Differences in IFN-gamma effect on ICAM-1 levels between HUVEC and HTEC monolayers were not due to differences in number or responsiveness of IFN-gamma receptors, because both cell types exhibited a similar number of receptors and other IFN-gamma-dependent responses of HUVECs remained active. In all analyses, ICAM-1 mRNA levels correlated closely with detection of ICAM-1 on the cell surface.(ABSTRACT TRUNCATED AT 250 WORDS)

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Modulation of airway inflammation and bacterial clearance by epithelial cell ICAM-1

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00073.2004 ◽

2004 ◽

Vol 287 (3) ◽

pp. L598-L607 ◽

Cited By ~ 22

Author(s):

Alicia L. Humlicek ◽

Liyi Pang ◽

Dwight C. Look

Keyword(s):

Epithelial Cell ◽

Epithelial Cells ◽

Airway Epithelial Cells ◽

Leukocyte Recruitment ◽

Intercellular Adhesion Molecule ◽

Additional Contribution ◽

Bacterial Clearance ◽

Airway Epithelial ◽

Intercellular Adhesion Molecule 1 ◽

Bacterial Killing

Many cell types in the airway express the adhesive glycoprotein for leukocytes intercellular adhesion molecule-1 (ICAM-1) constitutively and/or in response to inflammatory stimuli. In this study, we identified functions of ICAM-1 on airway epithelial cells in defense against infection with Haemophilus influenzae. Initial experiments using a mouse model of airway infection in which the bacterial inoculum was mixed with agar beads that localize inflammation in airways demonstrated that ICAM-1 expression was required for efficient clearance of H. influenzae. Airway epithelial cell ICAM-1 expression required few or no leukocytes, suggesting that epithelial cells could be activated directly by interaction with bacteria. Specific inhibition of ICAM-1 function on epithelial cells by orotracheal injection of blocking antibodies resulted in decreased leukocyte recruitment and H. influenzae clearance in the airway. Inhibition of endothelial cell ICAM-1 resulted in a similar decrease in leukocyte recruitment but did not affect bacterial clearance, indicating that epithelial cell ICAM-1 had an additional contribution to airway defense independent of effects on leukocyte migration. To assess this possibility, we used an in vitro model of neutrophil phagocytosis of bacteria and observed significantly greater engulfment of bacteria by neutrophils adherent to epithelial cells expressing ICAM-1 compared with nonadherent neutrophils. Furthermore, bacterial phagocytosis and killing by neutrophils after interaction with epithelial cells were decreased when a blocking antibody inhibited ICAM-1 function. The results indicate that epithelial cell ICAM-1 participates in neutrophil recruitment into the airway, but its most important role in clearance of H. influenzae may be assistance with neutrophil-dependent bacterial killing.

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