Polarized localization of epithelial CXCL11 in chronic obstructive pulmonary disease and mechanisms of T cell egression

Molecular cloning, characterization and expression analysis of the Chinese soft-shelled turtle (Pelodiscus sinensis) chemokine CXCL11

Chemokines are small, secreted proteins with chemoattractive properties, which play an important role in the recruitment and activation of immune cells. CXCL11 is a CXC chemokine specific for the CXCR3 receptors, which has been shown to mediate the generation of Th1-type immune responses and have bactericidal effects similar to defensins. Herein, we cloned the full-length cDNA of Chinese soft-shelled turtle (Pelodiscus sinensis) CXCL11, designated as PsCXCL11, which consist of an open reading frame (ORF) of 282 bp encoding 93 amino acids, with estimated molecular weight of 10.055 kDa and isoelectric point of 10.37. The deduced PsCXCL11 sequence had a signal peptide, a highly conserved family-specific small cytokine (SCY) domain, one putative N-glycosylation site and ten potential phosphorylation sites. Phylogenetic analysis showed a close relationship between P. sinensis and Chelydra Serpentina CXCL11. P. sinensis CXCL11 basal expression levels were higher in heart, kidney and spleen than in other organs of health turtles. Infections of Aeromonas hydrophila and Staphylococcus aureus led to significant upregulation of P. sinensis CXCL11 in the blood, while significant upregulation of PsCXCL11 were observed in liver and spleen after infection of A. hydrophila, but not S. aureus. PsCXCL11 recombinant protein with His-tag was successfully expressed by an auto-inducible expression system, and purified by Ni-NTA affinity chromatography. These findings laid a solid foundation for further research towards development of the Chinese soft-shelled turtle as a model for the role of CXCL11 in regulating inflammatory responses to stimulation by invading pathogens.

Study on Potential Differentially Expressed Genes in Idiopathic Pulmonary Fibrosis by Bioinformatics and Next-Generation Sequencing Data Analysis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease with reduced quality of life and earlier mortality, but its pathogenesis and key genes are still unclear. In this investigation, bioinformatics was used to deeply analyze the pathogenesis of IPF and related key genes, so as to investigate the potential molecular pathogenesis of IPF and provide guidance for clinical treatment. Next-generation sequencing dataset GSE213001 was obtained from Gene Expression Omnibus (GEO), and the differentially expressed genes (DEGs) were identified between IPF and normal control group. The DEGs between IPF and normal control group were screened with the DESeq2 package of R language. The Gene Ontology (GO) and REACTOME pathway enrichment analyses of the DEGs were performed. Using the g:Profiler, the function and pathway enrichment analyses of DEGs were performed. Then, a protein-protein interaction (PPI) network was constructed via the Integrated Interactions Database (IID) database. Cytoscape with Network Analyzer was used to identify the hub genes. miRNet and NetworkAnalyst databaseswereused to construct the targeted microRNAs (miRNAs), transcription factors (TFs), and small drug molecules. Finally, receiver operating characteristic (ROC) curve analysis was used to validate the hub genes. A total of 958 DEGs were screened out in this study, including 479 up regulated genes and 479 down regulated genes. Most of the DEGs were significantly enriched in response to stimulus, GPCR ligand binding, microtubule-based process, and defective GALNT3 causes HFTC. In combination with the results of the PPI network, miRNA-hub gene regulatory network and TF-hub gene regulatory network, hub genes including LRRK2, BMI1, EBP, MNDA, KBTBD7, KRT15, OTX1, TEKT4, SPAG8, and EFHC2 were selected. Cyclothiazide and rotigotinethe are predicted small drug molecules for IPF treatment. Our findings will contribute to identification of potential biomarkers and novel strategies for the treatment of IPF, and provide a novel strategy for clinical therapy.

Cigarette Smoking Contributes to Th1/Th2 Cell Dysfunction via the Cytokine Milieu in Chronic Obstructive Pulmonary Disease

Background

Dysregulation and pyroptosis of T-helper (Th) cells and inflammatory cytokines have been implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). However, the immune response mechanisms as a consequence of tobacco smoke exposure are not fully understood. We hypothesized that cigarette smoke-induced inflammation could be modulated through the cytokine milieu and T-cell nicotinic acetylcholine receptors (nAChRs).

Methods

The proportions of peripheral blood Th1 and Th2 cells from patients with COPD, smokers without airway obstruction and healthy nonsmokers were analyzed using flow cytometry. The levels of plasma proinflammatory cytokines and their potential association with pulmonary function were also measured. The influence of cigarette smoke extract (CSE) on the conditioned differentiation of T helper cell subsets was further examined in vitro.

Results

Significantly higher Th1 cell and plasma IFN-γ and IL-18 levels but lower levels of Th2 cells were found in the peripheral blood from patients with COPD. The increased plasma levels of IFN-γ and IL-18 were negatively correlated with pulmonary function (FEV1% predicted value). Pyroptosis participates in COPD development probably through the activation of the NLRP3 inflammasome upon exposure to CSE. CSE does not directly induce the differentiation of T helper cells; however, under conditioned medium, CSE promotes Th1 development through α7 nAChR modification, while it does not substantially interfere with Th2 differentiation.

Conclusion

The differences in the cytokine milieu play a key role in the effects of CSE on the immune response in patients with COPD.

Weight loss and abnormal lung inflammation in mice chronically exposed to secondary organic aerosols

Secondary organic aerosols (SOAs) have emerged recently as a major component of fine particulate matter. Cell culture studies revealed a role for SOAs in cell oxidative stress, toxicity and inflammation and only a few studies investigated short-term SOA exposure in animal models. Here, mice were chronically exposed to naphthalene-derived SOAs for one and two months. Weight monitoring indicated a marked mass loss, especially in females, following chronic exposure to SOAs. Significantly, a cytokine antibody microarray approach revealed SOA-induced abnormal lung inflammation similar to that seen in cigarette smoke-induced chronic obstructive pulmonary disease (COPD). This in vivo study testifies to the pathogenic role of sub-chronic SOA exposure on human health.

Adenosine A2A receptor controls the gateway of the choroid plexus

The choroid plexus (CP) is one of the key gateways regulating the entry of peripheral immune cells into the CNS. However, the neuromodulatory mechanisms of maintaining its gateway activity are not fully understood. Here, we identified adenosine A_2A receptor (A_2AR) activity as a regulatory signal for the activity of CP gateway under physiological conditions. In association with a tightly closed CP gateway, we found that A_2AR was present at low density in the CP. The RNA-seq analysis revealed that the A_2AR antagonist KW6002 affected the expression of the cell adhesion molecules' (CAMs) pathway and cell response to IFN-γ in the CP. Furthermore, blocking or activating A_2AR signaling in the CP resulted in a decreased and an increased, respectively, expression of lymphocyte trafficking determinants and disruption of the tight junctions (TJs). Furthermore, A_2AR signaling regulates the CP permeability. Thus, A_2AR activity in the CP may serve as a therapeutic target for remodeling the immune homeostasis in the CNS with implications for the treatment of neuroimmunological disorders.

Chemokines in COPD: From Implication to Therapeutic Use

: Chronic Obstructive Pulmonary Disease (COPD) represents the 3rd leading cause of death in the world. The underlying pathophysiological mechanisms have been the focus of extensive research in the past. The lung has a complex architecture, where structural cells interact continuously with immune cells that infiltrate into the pulmonary tissue. Both types of cells express chemokines and chemokine receptors, making them sensitive to modifications of concentration gradients. Cigarette smoke exposure and recurrent exacerbations, directly and indirectly, impact the expression of chemokines and chemokine receptors. Here, we provide an overview of the evidence regarding chemokines involvement in COPD, and we hypothesize that a dysregulation of this tightly regulated system is critical in COPD evolution, both at a stable state and during exacerbations. Targeting chemokines and chemokine receptors could be highly attractive as a mean to control both chronic inflammation and bronchial remodeling. We present a special focus on the CXCL8-CXCR1/2, CXCL9/10/11-CXCR3, CCL2-CCR2, and CXCL12-CXCR4 axes that seem particularly involved in the disease pathophysiology.

NFAT isoforms play distinct roles in TNFα-induced retinal leukostasis

The objective of this study was to determine the role of individual NFAT isoforms in TNFα-induced retinal leukostasis. To this end, human retinal microvascular endothelial cells (HRMEC) transfected with siRNA targeting individual NFAT isoforms were treated with TNFα, and qRT-PCR was used to examine the contribution of each isoform to the TNFα-induced upregulation of leukocyte adhesion proteins. This showed that NFATc1 siRNA increased ICAM1 expression, NFATc2 siRNA reduced CX3CL1, VCAM1, SELE, and ICAM1 expression, NFATc3 siRNA increased CX3CL1 and SELE expression, and NFATc4 siRNA reduced SELE expression. Transfected HRMEC monolayers were also treated with TNFα and assayed using a parallel plate flow chamber, and both NFATc2 and NFATc4 knockdown reduced TNFα-induced cell adhesion. The effect of isoform-specific knockdown on TNFα-induced cytokine production was also measured using protein ELISAs and conditioned cell culture medium, and showed that NFATc4 siRNA reduced CXCL10, CXCL11, and MCP-1 protein levels. Lastly, the CN/NFAT-signaling inhibitor INCA-6 was shown to reduce TNFα-induced retinal leukostasis in vivo. Together, these studies show a clear role for NFAT-signaling in TNFα-induced retinal leukostasis, and identify NFATc2 and NFATc4 as potentially valuable therapeutic targets for treating retinopathies in which TNFα plays a pathogenic role.

RNA-Seq reveals a role for NFAT-signaling in human retinal microvascular endothelial cells treated with TNFα

TNFα has been identified as playing an important role in pathologic complications associated with diabetic retinopathy and retinal inflammation, such as retinal leukostasis. However, the transcriptional effects of TNFα on retinal microvascular endothelial cells and the different signaling pathways involved are not yet fully understood. In the present study, RNA-seq was used to profile the transcriptome of human retinal microvascular endothelial cells (HRMEC) treated for 4 hours with TNFα in the presence or absence of the NFAT-specific inhibitor INCA-6, in order to gain insight into the specific effects of TNFα on RMEC and identify any involvement of NFAT signaling. Differential expression analysis revealed that TNFα treatment significantly upregulated the expression of 579 genes when compared to vehicle-treated controls, and subsequent pathway analysis revealed a TNFα-induced enrichment of transcripts associated with cytokine-cytokine receptor interactions, cell adhesion molecules, and leukocyte transendothelial migration. Differential expression analysis comparing TNFα-treated cells to those co-treated with INCA-6 revealed 10 genes whose expression was significantly reduced by the NFAT inhibitor, including those encoding the proteins VCAM1 and CX3CL1 and cytokines CXCL10 and CXCL11. This study identifies the transcriptional effects of TNFα on HRMEC, highlighting its involvement in multiple pathways that contribute to retinal leukostasis, and identifying a previously unknown role for NFAT-signaling downstream of TNFα.

IFN-γ-dependent activation of the brain's choroid plexus for CNS immune surveillance and repair

Infiltrating T cells and monocyte-derived macrophages support central nervous system repair. Although infiltration of leucocytes to the injured central nervous system has recently been shown to be orchestrated by the brain's choroid plexus, the immunological mechanism that maintains this barrier and regulates its activity as a selective gate is poorly understood. Here, we hypothesized that CD4(+) effector memory T cells, recently shown to reside at the choroid plexus stroma, regulate leucocyte trafficking through this portal through their interactions with the choroid plexus epithelium. We found that the naïve choroid plexus is populated by T helper 1, T helper 2 and regulatory T cells, but not by encephalitogenic T cells. In vitro findings revealed that the expression of immune cell trafficking determinants by the choroid plexus epithelium is specifically induced by interferon-γ. Tumour necrosis factor-α and interferon-γ reciprocally controlled the expression of their receptors by the choroid plexus epithelium, and had a synergistic effect in inducing the epithelial expression of trafficking molecules. In vivo, interferon-γ-dependent signalling controlled trafficking through the choroid plexus; interferon-γ receptor knockout mice exhibited reduced levels of T cells and monocyte entry to the cerebrospinal fluid and impaired recovery following spinal cord injury. Moreover, reduced expression of trafficking molecules by the choroid plexus was correlated with reduced CD4(+) T cells in the choroid plexus and cerebrospinal fluid of interferon-γ receptor knockout mice. Similar effect on the expression of trafficking molecules by the choroid plexus was found in bone-marrow chimeric mice lacking interferon-γ receptor in the central nervous system, or reciprocally, lacking interferon-γ in the circulation. Collectively, our findings attribute a novel immunological plasticity to the choroid plexus epithelium, allowing it to serve, through interferon-γ signalling, as a tightly regulated entry gate into the central nervous system for circulating leucocytes immune surveillance under physiological conditions, and for repair following acute injury.

Resolution of leucocyte-mediated mucosal diseases. A novel in vivo paradigm for drug development

Removal of disease-driving inflammatory leucocytes is central to resolution of inflammation. The current pharmacological dogma teaches leucocyte elimination through apoptosis followed by phagocytosis. However, actual resolving roles of apoptotic-phagocytic processes have been difficult to demonstrate in the major diseases that are characterized by mucosal tissue inflammation. Many current in vivo observations rather demonstrate that leucocyte elimination occurs by transepithelial locomotion. Findings in diseased gut and bladder mucosae support this notion. Respiratory disease data are particularly compelling. Eosinophils and neutrophils abound in sputum and tracheal aspirates during treatment-induced recovery from severe asthma. Prolonged sputum neutrophilia, along with clinical improvement, follows upon smoking cessation in COPD. Eosinophils, neutrophils, lymphocytes, mast cells and dendritic cells also move in large numbers into the bronchial lumen at spontaneous inflammation resolution following allergen challenge in allergic rhinitis and asthma. A corresponding reduction of infiltrated cells in the bronchial mucosal tissue demonstrates efficiency of the transepithelial elimination pathway. Underscoring its operational role, drugs impeding transepithelial elimination of leucocytes aggravate mucosal/parenchymal inflammation. Hence, relying on lumen cell data alone can lead to paradoxical conclusions regarding anti-inflammatory drug efficacy. Conversely, drugs promoting non-injurious transepithelial elimination of leucocytes could resolve mucosal inflammatory diseases.

Current concepts on oxidative/carbonyl stress, inflammation and epigenetics in pathogenesis of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a global health problem. The current therapies for COPD are poorly effective and the mainstays of pharmacotherapy are bronchodilators. A better understanding of the pathobiology of COPD is critical for the development of novel therapies. In the present review, we have discussed the roles of oxidative/aldehyde stress, inflammation/immunity, and chromatin remodeling in the pathogenesis of COPD. An imbalance of oxidants/antioxidants caused by cigarette smoke and other pollutants/biomass fuels plays an important role in the pathogenesis of COPD by regulating redox-sensitive transcription factors (e.g., NF-κB), autophagy and unfolded protein response leading to chronic lung inflammatory response. Cigarette smoke also activates canonical/alternative NF-κB pathways and their upstream kinases leading to sustained inflammatory response in lungs. Recently, epigenetic regulation has been shown to be critical for the development of COPD because the expression/activity of enzymes that regulate these epigenetic modifications have been reported to be abnormal in airways of COPD patients. Hence, the significant advances made in understanding the pathophysiology of COPD as described herein will identify novel therapeutic targets for intervention in COPD.

Resolution of cell-mediated airways diseases

"Inflammation resolution" has of late become a topical research area. Activation of resolution phase mechanisms, involving select post-transcriptional regulons, transcription factors, 'autacoids', and cell phenotypes, is now considered to resolve inflammatory diseases. Critical to this discourse on resolution is the elimination of inflammatory cells through apoptosis and phagocytosis. For major inflammatory diseases such as asthma and COPD we propose an alternative path to apoptosis for cell elimination. We argue that transepithelial migration of airway wall leukocytes, followed by mucociliary clearance, efficiently and non-injuriously eliminates pro-inflammatory cells from diseased airway tissues. First, it seems clear that numerous infiltrated granulocytes and lymphocytes can be speedily transmitted into the airway lumen without harming the epithelial barrier. Then there are a wide range of 'unexpected' findings demonstrating that clinical improvement of asthma and COPD is not only associated with decreasing numbers of airway wall inflammatory cells but also with increasing numbers of these cells in the airway lumen. Finally, effects of inhibition of transepithelial migration support the present hypothesis. Airway inflammatory processes have thus been much aggravated when transepithelial exit of leukocytes has been inhibited. In conclusion, the present hypothesis highlights risks involved in drug-induced inhibition of transepithelial migration of airway wall leukocytes. It helps interpretation of common airway lumen data, and suggests approaches to treat cell-mediated airway inflammation.

Mycobacterium tuberculosis upregulates microglial matrix metalloproteinase-1 and -3 expression and secretion via NF-kappaB- and Activator Protein-1-dependent monocyte networks

Inflammatory tissue destruction is central to pathology in CNS tuberculosis (TB). We hypothesized that microglial-derived matrix metalloproteinases (MMPs) have a key role in driving such damage. Analysis of all of the MMPs demonstrated that conditioned medium from Mycobacterium tuberculosis-infected human monocytes (CoMTb) stimulated greater MMP-1, -3, and -9 gene expression in human microglial cells than direct infection. In patients with CNS TB, MMP-1/-3 immunoreactivity was demonstrated in the center of brain granulomas. Concurrently, CoMTb decreased expression of the inhibitors, tissue inhibitor of metalloproteinase-2, -3, and -4. MMP-1/-3 secretion was significantly inhibited by dexamethasone, which reduces mortality in CNS TB. Surface-enhanced laser desorption ionization time-of-flight analysis of CoMTb showed that TNF-alpha and IL-1beta are necessary but not sufficient for upregulating MMP-1 secretion and act synergistically to drive MMP-3 secretion. Chemical inhibition and promoter-reporter analyses showed that NF-kappaB and AP-1 c-Jun/FosB heterodimers regulate CoMTb-induced MMP-1/-3 secretion. Furthermore, NF-kappaB p65 and AP-1 c-Jun subunits were upregulated in biopsy granulomas from patients with cerebral TB. In summary, functionally unopposed, network-dependent microglial MMP-1/-3 gene expression and secretion regulated by NF-kappaB and AP-1 subunits were demonstrated in vitro and, for the first time, in CNS TB patients. Dexamethasone suppression of MMP-1/-3 gene expression provides a novel mechanism explaining the benefit of steroid therapy in these patients.

Expressed gene sequence and bioactivity of the IFNgamma-response chemokine CXCL11 of swine and cattle

This report describes the cloning and characterization of expressed gene sequences of the swine and bovine interferon-gamma inducible chemokine CXCL11, or I-TAC, associated with type 1 T-helper immune responses, and affirmation of bioactivity of their yeast-expressed protein products. The coding regions of both cDNA sequences were 303 nucleotides in length; each is coded for four exons in the genome. The bovine coding region shared 82% and 70% homology with human and mouse CXCL11, respectively, and the swine coding region 84% and 72% homology, respectively. As expected the swine and bovine CXCL11 sequences showed less homology with other human and mouse C-X-C motif chemokine sequences. Each cDNA was cloned into plasmids and transfected into Pichia pastoris (yeast) and the resultant expressed protein purified. Biological activity of each purified chemokine was affirmed by chemotaxis assays. Both swine and bovine CXCL11 were chemotactic for mitogen and IL-2 stimulated peripheral blood mononuclear cells. This is the first report for bioactivity of this chemokine in livestock species. This work provides valuable new reagents for investigating basic immunity as well as vaccine and disease responses in swine and cattle, goals of the U.S. Veterinary Immune Reagent Network which supported this effort.

Mechanisms for transcellular diapedesis: probing and pathfinding by 'invadosome-like protrusions'

Immune-system functions require that blood leukocytes continuously traffic throughout the body and repeatedly cross endothelial barriers (i.e. diapedese) as they enter (intravasate) and exit (extravasate) the circulation. The very earliest studies to characterize diapedesis directly in vivo suggested the coexistence of two distinct migratory pathways of leukocytes: between (paracellular pathway) and directly through (transcellular pathway) individual endothelial cells. In vivo studies over the past 50 years have demonstrated significant use of the transcellular diapedesis pathway in bone marrow, thymus, secondary lymphoid organs, various lymphatic structures and peripheral tissues during inflammation and across the blood-brain barrier and blood-retinal barrier during inflammatory pathology. Recently, the first in vitro reports of transcellular diapedesis have emerged. Together, these in vitro and in vivo observations suggest a model of migratory pathfinding in which dynamic 'invadosome-like protrusions' formed by leukocytes have a central role in both identifying and exploiting endothelial locations that are permissive for transcellular diapedesis. Such 'probing' activity might have additional roles in this and other settings.

Bibliography. Current world literature

This bibliography is compiled by clinicians from the journals listed at the end of this publication. It is based on literature entered into our database between 1 November 2007 and 31 October 2008 (articles are generally added to the database about two and a half months after publication). In addition, the bibliography contains every paper annotated by reviewers; these references were obtained from a variety of bibliographic databases and published between the beginning of the review period and the time of going to press. The bibliography has been grouped into topics that relate to the reviews in this issue.

Sustained activation of STAT5 is essential for chromatin remodeling and maintenance of mammary-specific function

Epithelial cells, once dissociated and placed in two-dimensional (2D) cultures, rapidly lose tissue-specific functions. We showed previously that in addition to prolactin, signaling by laminin-111 was necessary to restore functional differentiation of mammary epithelia. Here, we elucidate two additional aspects of laminin-111 action. We show that in 2D cultures, the prolactin receptor is basolaterally localized and physically segregated from its apically placed ligand. Detachment of the cells exposes the receptor to ligation by prolactin leading to signal transducers and activators of transcription protein 5 (STAT5) activation, but only transiently and not sufficiently for induction of milk protein expression. We show that laminin-111 reorganizes mammary cells into polarized acini, allowing both the exposure of the prolactin receptor and sustained activation of STAT5. The use of constitutively active STAT5 constructs showed that the latter is necessary and sufficient for chromatin reorganization and β-casein transcription. These results underscore the crucial role of continuous laminin signaling and polarized tissue architecture in maintenance of transcription factor activation, chromatin organization, and tissue-specific gene expression.

Epithelial ICAM-1 and ICAM-2 regulate the egression of human T cells across the bronchial epithelium

Egression of inflammatory cells from the lung interstitium into the airway lumen is critical for the resolution of inflammation, but the underlying mechanisms of this egression are unclear. Here, we use an in vitro system, in which human T cells migrate across a bronchial epithelial monolayer, to investigate the molecules involved. We show that although inhibition of T-cell LFA-1 blocks egression by 75 ± 5.6% (P<0.0001), inhibition of the LFA-1-ligand ICAM-1 on the epithelium only inhibits by 52.7 ± 0.06% (P=0.0001). We, therefore, looked for other epithelial ligands for LFA-1 and demonstrate that ICAM-2, but not ICAM-3, is expressed on the bronchial epithelium. Blocking ICAM-2 inhibits egression by 50.95 ± 10.79% (P=0.04), and blocking both ICAM-1 and ICAM-2 inhibits egression by 69.6 ± 5.2% (P< 0.0001). Inhibition of LFA-1/ICAM-1 and ICAM-2 interactions on the basolateral epithelium does not prevent egressing T cells from adhering, polarizing, or moving over the basal epithelium, but it does prevent their recognition of the interepithelial junctions. In conclusion, we show that egression of T cells involves three distinct sequential steps: adhesion, junctional recognition, and diapedesis; we further demonstrate that ICAM-2 is expressed on the bronchial epithelium and, together with ICAM-1, has an essential function in the clearance of T cells from the lung.—Porter, J. C., Hall, A. Epithelial ICAM-1 and ICAM-2 regulate the egression of human T cells across the bronchial epithelium.

Epithelial Rho GTPases and the transepithelial migration of lymphocytes

Tissue injury and inflammation lead to leukocyte recruitment from the bloodstream into the inflamed organ. Because leukocytes in excessive numbers and over prolonged periods can cause tissue damage, it is important that the trafficking of leukocytes is regulated. Although much attention has been focused on leukocyte recruitment, much less is known about the resolution of inflammation. Hollow organs, such as the lung and the gut, are unique in that tissue accumulation of leukocytes is determined by the recruitment of leukocytes from the blood; survival of tissue leukocytes; and migration of leukocytes from the interstitial space, either to the lymphatics or into the lumen of the organ, so-called egression. It has been shown that preventing egression of peribronchial leukocytes in a murine model of bronchial inflammation was fatal. This has led to an interest in the molecular mechanisms underlying egression from the lung. We have used a human bronchial cell line, 16HBE14(0-), in vitro to analyze transepithelial migration and to investigate the role of Rho GTPases in this process. This chapter describes methods used to establish monolayers of bronchial epithelial cells either the correct way up or inverted on Transwell filters and describes an assay of transepithelial migration of primary human T lymphocytes across this monolayer. This chapter shows how this system can be used to dissect out the molecular events that are required for successful egression. In particular, pretreatment of either the lymphocytes or the epithelium with blocking antibodies against cell surface receptors or with cell-permeable inhibitors directed against signaling molecules allows an analysis of the individual roles played by the T lymphocytes and the epithelial monolayer.