Costimulation in Allergic Asthma: The Roles of B7 and Semaphorin Molecules

It is well established that allergic asthma is T cell-driven disease where CD4+ T cells of Th2 phenotype play a critical role in disease initiation and maintenance. There are several critical steps in the induction of Th2 type immune response to the allergen. The first critical step is the antigen processing and presentation of allergen-derived peptides in the context of specific major histocompatibility Class II (MHCII) molecules by antigen-presenting cells (APC). Recognition of this complex by T cell receptor (TCR) and interaction of costimulatory ligands with corresponding receptors represents the second step in T cell activation. As the third part of optimal T cell differentiation, proliferation, and expansion, several cytokines, integrins, and chemokines get involved in the fine-tuning of DC-T cell interaction and activation. Multiple recent evidences point to the selected members of B7 and semaphorin families as important checkpoints providing a fine-tuning regulation of immune response. In this book chapter, we discuss the properties of costimulatory molecules and address their roles in allergic asthma

Transfer of in vivo primed transgenic T cells supports allergic lung inflammation and FIZZ1 and Ym1 production in an IL-4Rα and STAT6 dependent manner

<p>Abstract</p> <p>Background</p> <p>CD4+ T helper type 2 (T_H2) cells, their cytokines IL-4, IL-5 and IL-13 and the transcription factor STAT6 are known to regulate various features of asthma including lung inflammation, mucus production and airway hyperreactivity and also drive alternative activation of macrophages (AAM). However, the precise roles played by the IL-4/IL-13 receptors and STAT6 in inducing AAM protein expression and modulating specific features of airway inflammation are still unclear. Since T_H2 differentiation and activation plays a pivotal role in this disease, we explored the possibility of developing an asthma model in mice using T cells that were differentiated <it>in vivo</it>.</p> <p>Results</p> <p>In this study, we monitored the activation and proliferation status of adoptively transferred allergen-specific naïve or <it>in vivo </it>primed CD4+ T cells. We found that both the naïve and <it>in vivo </it>primed T cells expressed similar levels of CD44 and IL-4. However, <it>in vivo </it>primed T cells underwent reduced proliferation in a lymphopenic environment when compared to naïve T cells. We then used these <it>in vivo </it>generated effector T cells in an asthma model. Although there was reduced inflammation in mice lacking IL-4Rα or STAT6, significant amounts of eosinophils were still present in the BAL and lung tissue. Moreover, specific AAM proteins YM1 and FIZZ1 were expressed by epithelial cells, while macrophages expressed only YM1 in RAG2^-/-mice. We further show that FIZZ1 and YM1 protein expression in the lung was completely dependent on signaling through the IL-4Rα and STAT6. Consistent with the enhanced inflammation and AAM protein expression, there was a significant increase in collagen deposition and smooth muscle thickening in RAG2^-/-mice compared to mice deficient in IL-4Rα or STAT6.</p> <p>Conclusions</p> <p>These results establish that transfer of <it>in vivo </it>primed CD4+ T cells can induce allergic lung inflammation. Furthermore, while IL-4/IL-13 signaling through IL-4Rα and STAT6 is essential for AAM protein expression, lung inflammation and eosinophilia are only partially dependent on this pathway. Further studies are required to identify other proteins and signaling pathways involved in airway inflammation.</p

Expression of neuroimmune semaphorins 4A and 4D and their receptors in the lung is enhanced by allergen and vascular endothelial growth factor

<p>Abstract</p> <p>Background</p> <p>Semaphorins were originally identified as molecules regulating <b>a </b>functional activity of axons in the nervous system. Sema4A and Sema4D were the first semaphorins found to be expressed on immune cells and were termed "immune semaphorins". It is known that Sema4A and Sema4D bind Tim-2 and CD72 expressed on leukocytes and PlexinD1 and B1 present on non-immune cells. These neuroimmune semaphorins and their receptors have been shown to play critical roles in many physiological and pathological processes including neuronal development, immune response regulation, cancer, autoimmune, cardiovascular, renal, and infectious diseases. However, the expression and regulation of Sema4A, Sema4D, and their receptors in normal and allergic lungs is undefined.</p> <p>Results</p> <p>Allergen treatment and lung-specific vascular endothelial growth factor (VEGF) expression induced asthma-like pathologies in the murine lungs. These experimental models of allergic airway inflammation were used for the expression analysis of immune semaphorins and their receptors employing immunohistochemistry and flow cytometry techniques. We found that besides accessory-like cells, Sema4A was also detected on bronchial epithelial and smooth muscle cells, whereas Sema4D expression was high on immune cells such as T and B lymphocytes. Surprisingly, under inflammation various cell types including macrophages, lymphocytes, and granulocytes in the lung expressed Tim-2, a previously defined marker for Th2 cells. CD72 was found on lung immune, inflammatory, and epithelial cells. Bronchial epithelial cells were positive for both plexins, whereas some endothelial cells selectively expressed Plexin D1. Plexin B1 expression was also detected on lung DC. Both allergen and VEGF upregulated the expression of neuroimmune semaphorins and their receptors in the lung tissue. However, the lung tissue Sema4A-Tim2 expression was rather weak, whereas Sema4D-CD72 ligand-receptor pair was vastly upregulated by allergen. Soluble Sema4D protein was present in the lung lysates and a whole Sema4A protein plus its dimer were readily detected in the bronchoalveolar (BAL) fluids under inflammation.</p> <p>Conclusions</p> <p>This study clearly shows that neuroimmune semaphorins Sema4A and Sema4D and their receptors might serve as potential markers for the allergic airway inflammatory diseases. Our current findings pave the way for further investigations of the role of immune semaphorins in inflammation and their use as potential therapeutic targets for the inflammatory lung conditions.</p

Early Growth Response Gene 1–mediated Apoptosis Is Essential for Transforming Growth Factor β1–induced Pulmonary Fibrosis

Fibrosis and apoptosis are juxtaposed in pulmonary disorders such as asthma and the interstitial diseases, and transforming growth factor (TGF)-β1 has been implicated in the pathogenesis of these responses. However, the in vivo effector functions of TGF-β1 in the lung and its roles in the pathogenesis of these responses are not completely understood. In addition, the relationships between apoptosis and other TGF-β1–induced responses have not been defined. To address these issues, we targeted bioactive TGF-β1 to the murine lung using a novel externally regulatable, triple transgenic system. TGF-β1 produced a transient wave of epithelial apoptosis that was followed by mononuclear-rich inflammation, tissue fibrosis, myofibroblast and myocyte hyperplasia, and septal rupture with honeycombing. Studies of these mice highlighted the reversibility of this fibrotic response. They also demonstrated that a null mutation of early growth response gene (Egr)-1 or caspase inhibition blocked TGF-β1–induced apoptosis. Interestingly, both interventions markedly ameliorated TGF-β1–induced fibrosis and alveolar remodeling. These studies illustrate the complex effects of TGF-β1 in vivo and define the critical role of Egr-1 in the TGF-β1 phenotype. They also demonstrate that Egr-1–mediated apoptosis is a prerequisite for TGF-β1–induced fibrosis and remodeling