Ephrin-A1 suppresses Th2 cell activation and provides a regulatory link to lung epithelial cells

Gene expression screening showed decreased ephrin-A1 expression in CD4+ T cells of asthma patients. Ephrin-A1 is the ligand of the Eph receptor family of tyrosine kinases, forming the largest family of receptor tyrosine kinases. Their immune regulatory properties are largely unknown. This study demonstrates significantly reduced ephrin-A1 expression in T cells of asthma patients using real time-PCR. Immunohistological analyses revealed strong ephrin-A1 expression in lung tissue and low expression in cortical areas of lymph nodes. It is absent in T cell/B cell areas of the spleen. Colocalization of ephrin-A1 and its receptors was found only in the lung, but not in lymphoid tissues. In vitro activation of T cells reduced ephrin-A1 at mRNA and protein levels. T cell proliferation, activation-induced, and IL-2-dependent cell death were inhibited by cross-linking ephrin-A1, and not by engagement of Eph receptors. However, anti-EphA1 receptor slightly enhances Ag-specific and polyclonal proliferation of PBMC cultures. Furthermore, activation-induced CD25 up-regulation was diminished by ephrin-A1 engagement. Ephrin-A1 engagement reduced IL-2 expression by 82% and IL-4 reduced it by 69%; the IFN-gamma expression remained unaffected. These results demonstrate that ephrin-A1 suppresses T cell activation and Th2 cytokine expression, while preventing activation-induced cell death. The reduced ephrin-A1 expression in asthma patients may reflect the increased frequency of activated T cells in peripheral blood. That the natural ligands of ephrin-A1 are most abundantly expressed in the lung may be relevant for Th2 cell regulation in asthma and Th2 cell generation by mucosal allergens.

T cell phenotype in allergic asthma and atopic dermatitis

BACKGROUND

T cells are key regulators of immunologic disease parameters. However, their contribution to the process of tissue remodeling is ill defined. In the present study, we investigated gene expression of allergy-characteristic, IL-4-rich T cell cDNAs to monitor expression of genes that might participate in the pathogenesis of allergic diseases.

METHODS

cDNAs of freshly isolated and restimulated CD4+ T cells from patients with allergic asthma (AA) or atopic dermatitis (AD) and healthy subjects were analyzed on Nylon membrane-based DNA arrays. Three patients were selected for an allergy-characteristic T cell phenotype with high IL-4 expression (AA) or IL-13 expression (AD).

RESULTS

Several gene families such as the TGF-beta family, chemokines and chemokine receptors were found to be upregulated. Matrix metalloproteinases and their inhibitors were also found to be expressed in an enhanced manner. Furthermore, factors regulating tissue turnover such as fibroblast growth factors and neurotrophic as well as vasoactive factors were found be expressed at a higher level in allergic patient compared to healthy donors.

CONCLUSION

The present study reveals and confirms genes relevant for allergy and highlights an approach to applying a DNA array technique for diagnostic discrimination of allergic diseases.

Histamine enhances TGF-beta1-mediated suppression of Th2 responses

Susceptibility of T cells to TGF-beta1 produced by regulatory T cells has an important impact on the induction and maintenance of peripheral tolerance and therefore on the development of autoimmunity, cancer, and allergy. Histamine not only mediates the deleterious effects of allergic reactions, it can also modulate the Th1/Th2 cell balance. We demonstrate that histamine dose-dependently enhanced TGF-beta1-mediated suppression and TGF-beta1 responsiveness of CD4+ T cells. This effect was mediated by the histamine 2 receptor (H2R), as demonstrated by receptor-specific agonists and antagonists. Furthermore, the histamine effect on TGF-beta1 responsiveness was cAMP/PKA dependent. This pathway is activated by the H2R, which is preferentially expressed on Th2 cells. Thus a higher additive effect of histamine on TGF-beta1 responsiveness was found in Th2 cells compared with Th1 cells. In fact, findings are confirmed by analysis of cytokine regulation, since activation of the H2R/cAMP pathway promoted TGF-beta1-mediated IL-4 inhibition but was ineffective in suppressing IFN-gamma. These results demonstrate that histamine supports TGF-beta1 susceptibility of T cells. Moreover, Th2 cells are more affected by histamine-enhanced TGF-beta1 suppression, which is particularly important for the regulation of allergen-specific T cells in allergic immune responses.

SARA and Hgs attenuate susceptibility to TGF-beta1-mediated T cell suppression

Transforming growth factor-beta1 (TGF-beta1) is a pluripotent cytokine that controls peripheral T cell tolerance mainly in mucosal immunity. It is secreted by regulatory T cells (Tr /Th3) but also by other immununologically active cells. Smad anchor for receptor activation (SARA) and hepatic growth factor-regulated tyrosine kinase substrate (Hgs) are involved in TGF-beta1 signaling. Both molecules are known to present Smad2 and Smad3 to the TGF-beta receptor complex. The role of SARA and Hgs in TGF-beta1 susceptibility of human CD4+ T cells is unclear. We demonstrate here that TGF-beta1 up-regulates SARA mRNA expression in CD4+ T cells similar to that of Smad7. However, the increase in SARA expression was lower (6.1+/-0.3-fold vs. 25+/-4.1-fold) compared with Smad7 and delayed, with a maximum at 12 h compared with 2 h. Th1 and Th2 cell subsets expressed the same levels of SARA and Hgs. Compared with resting cells, significantly lower levels of the two molecules were found in antigen/allergen- or anti-CD3/CD28-stimulated cells. Down-regulation of SARA and Hgs mRNA in preactivated CD4+ T cells was accompanied by a twofold increase in a TGF-beta1 responsive reporter gene assay. Overexpression of SARA and Hgs in T cells yielded a dose-dependent decrease in cotransfected reporter gene expression, indicating an inhibitory function of both molecules. Thus, SARA and Hgs are regulators of TGF-beta1 susceptibility in T cells and integrate regulatory signals into the influence of TGF-beta1-mediated suppression of human T cells.

The phosphatidylinositol phosphatase PTEN is under control of costimulation and regulates proliferation in human T cells

The phosphatidylinositol phosphatase gene PTEN is a dual specific phosphatase acting on phospho amino acids but also on three phosphorylated inositol phospholipids. Present results demonstrate that PTEN is inducible by costimulatory signals in human CD4(+) T cells. PTEN expression was up-regulated on RNA and protein level in freshly isolated human CD4(+) T cells following stimulation with CD28 or CD2. In contrast, PTEN expression was high but remained CD28 and CD2 unresponsive in lymphoma cells. Intracellular staining revealed PTEN expression in CD4(+) T cell populations stimulated with anti-CD28 or anti-CD28 / anti-CD3. Stimulation with anti-CD3 alone did not induce PTEN expression. Inhibition of PTEN expression by antisense oligonucleotides in CD4(+) T cells stimulated with non-mitogenic anti-CD28 resulted in massively increased proliferation, which was sensitive to the phosphatidylinositol 3-kinase (PI3 K) inhibitor wortmannin. Although CD28 and CD2 induce PI3 K signal transduction, wortmannin did not block PTEN up-regulation by CD28 or CD2 indicating that PTEN gene expression is PI3 K independent. These results demonstrate that PTEN negatively controls costimulatory signals by antagonizing PI3 K activity in the absence of TCR engagement.

DNA arrays in allergy and immunology

The DNA array technique allows the simultaneous analysis of multiple genes. This makes it an interesting tool for studies of gene expression in various diseases that are caused by or depend on multiple genes. DNA arrays are particularly applied to define certain immunological conditions such as allergic diseases. We summarize strategies on gene expression profiling of inflammatory disease and immunologically relevant cells using DNA array technology. Using DNA arrays, gene expression analysis of CD4+ T cells of allergy patients revealed interesting differences compared to healthy individuals, but also between different allergic conditions. This comparison demonstrated that T cells differed in their capacity to regulate peripheral tolerance, neuronal innervation, chemotaxis, neovascularization and epidermal growth. On the basis of these findings the DNA array technique appears to be especially interesting for the development of powerful diagnostic tools allowing fine specification and subtyping of allergic conditions, monitoring of therapy and of tailored therapy concepts.