Signal transduction events regulating integrin function and T cell migration: new functions and complexity

Blood-brain barrier on a chip

The blood-brain barrier (BBB) plays a vital role in the maintenance of brain homeostasis. It strictly restricts the passage of molecules from the brain vasculature into the brain via its high transendothelial electrical resistance and low paracellular and transcellular permeability. Specialized brain endothelial cells, astrocytes, pericytes, neurons, and microglia contribute synergistically to the functional properties of the BBB. Because of its complexity and relative inaccessibility, BBB research is fraught with difficulties. Most studies rely on animal or cell culture models, which are not able to fully recapitulate the properties of the human BBB. The recent development of three-dimensional (3D) microfluidic models of the BBB could address this issue. This chapter aims to provide an overview of the recent advances in modeling the BBB on microdevices, and illustrate important considerations for the design of such models. In addition, protocols for the fabrication of a 3D BBB microfluidic chip and BBB assessment experiments, including immunocytochemistry for analyzing cell morphology and protein marker expression, permeability assay, and calcium imaging for studying neuronal function as a measure of BBB integrity, are presented here. It is envisioned that continued advancements in microtechnology can lead to the creation of realistic in vivo-like BBB-on-chip models.

The p110δ subunit of PI3K regulates bone marrow-derived eosinophil trafficking and airway eosinophilia in allergen-challenged mice

Trafficking and recruitment of eosinophils during allergic airway inflammation is mediated by the phosphatidylinositol 3-kinase (PI3K) family of signaling molecules. The role played by the p110δ subunit of PI3K (PI3K p110δ) in regulating eosinophil trafficking and recruitment was investigated using a selective pharmacological inhibitor (IC87114). Treatment with the PI3K p110δ inhibitor significantly reduced murine bone marrow-derived eosinophil (BM-Eos) adhesion to VCAM-1 as well as ICAM-1 and inhibited activation-induced changes in cell morphology associated with reduced Mac-1 expression and aberrant cell surface localization/distribution of Mac-1 and α4. Infused BM-Eos demonstrated significantly decreased rolling and adhesion in inflamed cremaster muscle microvessels of mice treated with IC87114 compared with vehicle-treated mice. Furthermore, inhibition of PI3K p110δ significantly attenuated eotaxin-1-induced BM-Eos migration and prevented eotaxin-1-induced changes in the cytoskeleton and cell morphology. Knockdown of PI3K p110δ with siRNA in BM-Eos resulted in reduced rolling, adhesion, and migration, as well as inhibition of activation-induced changes in cell morphology, validating its role in regulating trafficking and migration. Finally, in a mouse model of cockroach antigen-induced allergic airway inflammation, oral administration of the PI3K p110δ inhibitor significantly inhibited airway eosinophil recruitment, resulting in attenuation of airway hyperresponsiveness in response to methacholine, reduced mucus secretion, and expression of proinflammatory molecules (found in inflammatory zone-1 and intelectin-1). Overall, these findings indicate the important role played by PI3K p110δ in mediating BM-Eos trafficking and migration by regulating adhesion molecule expression and localization/distribution as well as promoting changes in cell morphology that favor recruitment during inflammation.

Age-related defects in the cytoskeleton signaling pathways of CD4 T cells

It has been postulated that the cytoskeleton controls many aspects of T cell function, including activation, proliferation and apoptosis. Recent advances in our understanding of F-actin polymerization and the Ezrin-Radixin-Moesin (ERM) family of cytoskeleton signal proteins have provided new insights into immunological synapse formation during T cell activation. During aging there is a significant decline of T cell function largely attributable to declines in activation of CD4 T cells and defects in the formation of the immunological synapse. Here we discuss recent progress in the understanding of how aging alters F-actin and ERM proteins in mouse CD4 T cells, and the implications of these changes for the T cell activation process.

The effector functions of mature T lymphocytes are impaired in transgenic mice expressing the SH2 domain of TSAd/Lad

TSAd/Lad is a T cell adaptor molecule involved in p56(lck)-mediated T cell activation. To investigate the functions of TSAd in T cells, we generated transgenic (TG) mice expressing the SH2 domain of TSAd (TSAd-SH2) under the control of the p56(lck) proximal promoter. In T cells from TSAd-SH2 TG mice, T cell receptor (TCR)-mediated early signaling events, such as Ca(2+) flux and ERK activation, were normal; however, late activation events, such as IL-2 production and proliferation, were significantly reduced. Moreover, TCR-induced cell adhesion to extracellular matrix (ECM) proteins and migration through ECM proteins were defective in T cells from TSAd-SH2 TG mice. Furthermore, the contact hypersensitivity (CHS) reaction, an inflammatory response mainly mediated by T helper 1 (Th1) cells, was inhibited in TSAd-SH2 TG mice. Taken together, these results show that TSAd, particularly the SH2 domain of TSAd, is essential for the effector functions of T cells.

Down-regulation of stromal cell-derived factor-1alpha-induced T cell chemotaxis by a peptide based on the complementarity-determining region 1 of an anti-DNA autoantibody via up-regulation of TGF-beta secretion

Systemic lupus erythematosus (SLE) can be induced in mice by immunizing them with a monoclonal human anti-DNA Ab that expresses a major Id, designated 16/6Id. In addition, a peptide based on the sequence of the CDR 1 (hCDR1) of the 16/6Id ameliorated the clinical manifestations of SLE in experimental models. In this study we examined the effects of treating mice with human complementary-determining region 1 (hCDR1) on the subsequent chemotaxis of T cells derived from 16/6Id-primed mice. First we demonstrated elevated levels of stromal cell-derived factor-1alpha (SDF-1alpha) in the sera of SLE-afflicted mice and in the sera and lymphoid tissues of 16/6Id-immunized BALB/c mice shortly after the immunization. We then found that administration of hCDR1 to 16/6Id-immunized mice specifically down-regulated SDF1alpha-induced T cell chemotaxis through fibronectin and collagen type I. This was accompanied by diminished SDF1-alpha-induced T cell adhesion and ERK phosphorylation. Treatment with hCDR1 up-regulated TGF-beta secretion, which, in turn, inhibited the murine T cell adhesion to and chemotaxis through fibronectin as well as their ERK phosphorylation. Thus, the secretion of TGF-beta after treatment of 16/6Id-immunized mice with hCDR1 plays an important role in the down-regulation of SDF-1alpha-mediated T cell activation and the interactions with extracellular matrix moieties observed in the present study.

Active participation of endothelial cells in inflammation

Leukocyte migration from the blood into tissues is vital for immune surveillance and inflammation. During this diapedesis of leukocytes, the leukocytes bind to endothelial cell adhesion molecules and then migrate across the vascular endothelium. Endothelial cell adhesion molecules and their counter-receptors on leukocytes generate intracellular signals. This review focuses on the active function of endothelial cells during leukocyte-endothelial cell interactions. We include a discussion of the "outside-in" signals in endothelial cells, which are stimulated by antibody cross-linking or leukocyte binding to platelet-endothelial cell adhesion molecule-1, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1. Some of these signals in endothelial cells have been demonstrated to actively participate in leukocyte migration. We suggest that some of the adhesion molecule signals, which have not been assigned a function, are consistent with signals that stimulate retraction of lateral junctions, stimulate endothelial cell basal surface adhesion, or induce gene expression.

The T cell cometh: interplay between adaptive immunity and cytokine networks in rheumatoid arthritis

The etiology of autoimmunity in humans remains poorly defined, and animal models provide a unique opportunity to study potential autoimmune mechanisms. A novel model of autoimmune inflammatory arthritis results from a point mutation in the zeta-associated-protein of 70 kDa (ZAP-70), which causes abnormal thymic T cell selection and survival of autoreactive clones. Although the resulting clinical and pathologic abnormalities are clearly T cell-dependent, macrophage and fibroblast cytokines such as IL-1 and TNF-alpha are required for full expression of the disease. The studies of Hata et al. raise the intriguing possibility that traditional proinflammatory cytokine networks represent common effector mechanisms in inflammatory joint diseases such as rheumatoid arthritis. Hence, effective therapeutic interventions can target either unique etiologic pathways related to adaptive immune responses or shared terminal mechanisms.

Control of TCR-Mediated Activation of β1 Integrins by the ZAP-70 Tyrosine Kinase Interdomain B Region and the Linker for Activation of T Cells Adapter Protein

One of the earliest functional responses of T lymphocytes to extracellular signals that activate the Ag-specific CD3/TCR complex is a rapid, but reversible, increase in the functional activity of integrin adhesion receptors. Previous studies have implicated the tyrosine kinase zeta-associated protein of 70 kDa (ZAP-70) and the lipid kinase phosphatidylinositol 3-kinase, in the activation of beta(1) integrins by the CD3/TCR complex. In this report, we use human ZAP-70-deficient Jurkat T cells to demonstrate that the kinase activity of ZAP-70 is required for CD3/TCR-mediated increases in beta(1) integrin-mediated adhesion and activation of phosphatidylinositol 3-kinase. A tyrosine to phenylalanine substitution at position 315 in the interdomain B of ZAP-70 inhibits these responses, whereas a similar substitution at position 292 enhances these downstream signals. These mutations in the ZAP-70 interdomain B region also specifically affect CD3/TCR-mediated tyrosine phosphorylation of residues 171 and 191 in the cytoplasmic domain of the linker for activation of T cells (LAT) adapter protein. CD3/TCR signaling to beta(1) integrins is defective in LAT-deficient Jurkat T cells, and can be restored with expression of wild-type LAT. Mutant LAT constructs with tyrosine to phenylalanine substitutions at position 171 and/or position 191 do not restore CD3/TCR-mediated activation of beta(1) integrins in LAT-deficient T cells. Thus, these studies demonstrate that the interdomain B region of ZAP-70 regulates beta(1) integrin activation by the CD3/TCR via control of tyrosine phosphorylation of tyrosine residues 171 and 191 in the LAT cytoplasmic domain.

Chemokines: roles in leukocyte development, trafficking, and effector function

Chemokines, representing a large superfamily of 8- to 15-kd proteins, were originally discovered through their ability to recruit various cell types into sites of inflammation. It is now clear that these molecules play a much wider role in immune homeostasis, playing key roles in driving the maturation, homing, and activation of leukocytes. In this review we analyze the roles chemokines play in the development, recruitment, and activation of leukocytes. Because signaling from the receptors drives these processes, signal transduction from chemokine receptors will also be reviewed. Taken together, we highlight the various points at which chemokines contribute to allergic inflammation and at which their targeting might contribute to new therapies for type I hypersensitivity reactions.