IFN-gamma regulation of ICAM-1 receptors in bronchial epithelial cells: soluble ICAM-1 release inhibits human rhinovirus infection.

BACKGROUND: Intercellular adhesion molecule-1 (ICAM-1) is a critical target-docking molecule on epithelial cells for 90% of human rhinovirus (HRV) serotypes. Two forms of ICAM-1 exist, membranous (mICAM-1) and soluble (sICAM-1), both expressed by bronchial epithelial cells. Interferon-gamma (IFN-gamma), a crucial Th-1 immuno-regulatory mediator, can modulate mICAM-1 expression; however its simultaneous effects on mICAM-1: sICAM-1 levels and their consequent outcome on cell infectivity have not been previously explored. METHODS: Primary normal human bronchial epithelial cells were pre-stimulated with IFN-gamma (1 ng/ml for 24 h) and subsequently inoculated with HRV-14 or HRV-1b (TCID50 10 2.5). Epithelial surface ICAM-1 expression and soluble ICAM-1 release were measured at the protein and gene level by immunofluorescence and ELISA respectively; mRNA levels were semi-quantified using RT-PCR. Molecular mechanisms regulating ICAM-1 isoform expression and effects on epithelial cell infectivity were explored. RESULTS: In IFN-gamma-biased cells infected with HRV-14, but not HRV-1b, mICAM-1 expression is down-regulated, with simultaneous induction of sICAM-1 release. This differential effect on HRV-14 receptor isoforms appears to be related to a combination of decreased IFN-gamma-induced JAK-STAT signalling and proteolytic receptor cleavage of the membranous form in IFN-gamma-biased HRV-14 infected cells. The observed changes in relative mICAM-1: sICAM-1 expression levels are associated with reduced HRV-14 viral titres. CONCLUSION: These findings support the hypothesis that in epithelial cells conditioned to IFN-gamma and subsequently exposed to HRV-14 infection, differential modulation in the ratio of ICAM-1 receptors prevails in favour of an anti-viral milieu, appearing to limit further target cell viral attachment and propagation.

Optical coherence tomography: real-time imaging of bronchial airways microstructure and detection of inflammatory/neoplastic morphologic changes.

PURPOSE: Current diagnostic imaging modalities for human bronchial airways do not possess sufficient resolution and tissue penetration depth to detect early morphologic changes and to differentiate in real-time neoplastic pathology from nonspecific aberrations. Optical coherence tomography (OCT) possesses the requisite high spatial resolution for reproducible delineation of endobronchial wall profiling. EXPERIMENTAL DESIGN: To establish whether OCT could differentiate between the composite microstructural layers of the human airways and simultaneously determine in situ morphologic changes, using a bench-top OCT system, we obtained cross-sectional images of bronchi from 15 patients undergoing lung resections for cancer. All scanned sections underwent subsequent detailed histologic analysis, allowing direct comparisons to be made. RESULTS: OCT imaging enables characterization of the multilayered microstructural anatomy of the airways, with a maximum penetration depth up to 2 to 3 mm and 10-microm spatial resolution. The epithelium, subepithelial components, and cartilage are individually defined. The acquired OCT images closely match histologically defined patterns in terms of structural profiles. Furthermore, OCT identifies in situ morphologic changes associated with inflammatory infiltrates, squamous metaplasia, and tumor presence. CONCLUSIONS: Our results confirm that OCT is a highly feasible optical tool for real-time near-histologic imaging of endobronchial pathology, with potential for lung cancer surveillance applications in diagnosis and treatment.

Human rhinovirus selectively modulates membranous and soluble forms of its intercellular adhesion molecule-1 (ICAM-1) receptor to promote epithelial cell infectivity.

Human rhinoviruses are responsible for many upper respiratory tract infections. 90% of rhinoviruses utilize intercellular adhesion molecule-1 (ICAM-1) as their cellular receptor, which also plays a critical role in recruitment of immune effector cells. Two forms of this receptor exist; membrane-bound (mICAM-1) and soluble ICAM-1 (sICAM-1). The soluble receptor may be produced independently from the membrane-bound form or it may be the product of proteolytic cleavage of mICAM-1. The ratio of airway epithelial cell expression of mICAM-1 to the sICAM-1 form may influence cell infectivity and outcome of rhinovirus infection. We therefore investigated the effect of rhinovirus on expression of both ICAM-1 receptors in normal human bronchial epithelial cells. We observed separate distinct messenger RNA transcripts coding for mICAM-1 and sICAM-1 in these cells, which were modulated by virus. Rhinovirus induced mICAM-1 expression on epithelial cells while simultaneously down-regulating sICAM-1 release, with consequent increase in target cell infectivity. The role of protein tyrosine kinases was investigated as a potential mechanistic pathway. Rhinovirus infection induced rapid phosphorylation of intracellular tyrosine kinase, which may be critical in up-regulation of mICAM-1. Elucidation of the underlying molecular mechanisms involved in differential modulation of both ICAM-1 receptors may lead to novel therapeutic strategies.