Elżbieta Sawicka

The sphingosine 1-phosphate receptor agonist FTY720 is a novel immunomodulator that sequesters lymphocytes in secondary lymphoid organs and thereby prevents their migration to sites of inflammation. However, there is currently no information available on whether this drug affects Th1 or Th2 cell-mediated lung-inflammatory responses. The effect of FTY720 was therefore investigated in a murine airway inflammation model using OVA-specific, in vitro differentiated, and adoptively transferred Th1 and Th2 cells. Both Th1 and Th2 cells express a similar pattern of FTY720-targeted sphingosine 1-phosphate receptors. The OVA-induced Th1-mediated airway inflammation characterized by increased numbers of lymphocytes and neutrophils in bronchoalveolar lavage fluid was significantly inhibited by oral FTY720 treatment. Similarly, FTY720 suppressed the Th2 cell-induced bronchoalveolar lavage fluid eosinophilia and the infiltration of T lymphocytes and eosinophils into the bronchial tissue. Moreover, the Ag-induced bronchial hyperresponsiveness to inhaled metacholine was almost completely blocked. The inhibitory effect of FTY720 on airway inflammation, induction of bronchial hyperresponsiveness, and goblet cell hyperplasia could be confirmed in an actively Ag-sensitized murine asthma model, clearly indicating that Th2 cell-driven allergic diseases such as asthma could benefit from such treatment.

The sphingosine 1-phosphate (S1P) receptor agonist FTY720 is well known for its immunomodulatory activity, sequestering lymphocytes from blood and spleen into secondary lymphoid organs and thereby preventing their migration to sites of inflammation. Because inflammation is critically dependent on a balance between Ag-specific Th/effector cells and T-regulatory cells, we investigated the effect of FTY720 on T-regulatory cell trafficking and functional activity. An increased number of CD4+/CD25+ T cells was found in blood and spleens of FTY720-treated mice, and transfer of these cells resulted in a significantly more pronounced accumulation in spleens but not lymph nodes after treatment, suggesting that this compound differentially affects the homing properties of T-regulatory cells compared with other T cell subsets. Indeed, CD4+/CD25+ T cells express lower levels of S1P1 and S1P4 receptors and demonstrate a reduced chemotactic response to S1P. Moreover, analysis of the functional response of FTY720-treated CD4+/CD25+ T cells revealed an increased suppressive activity in an in vitro Ag-specific proliferation assay. This correlated with enhanced function in vivo, with T-regulatory cells obtained from FTY720-treated mice being able to suppress OVA-induced airway inflammation. Thus, FTY720 differentially affects the sequestration of T-regulatory cells and importantly, increases the functional activity of T-regulatory cells, suggesting that it may have disease-modifying potential in inflammatory disorders.

We and others have established an important role for phosphoinositide-3 kinase gamma (PI3Kgamma) in the chemotactic responses of macrophages and neutrophils. The involvement of this lipid kinase in allergic inflammatory responses is, however, yet to be fully determined. Here we compare wild-type (WT) and PI3Kgamma(-/-) (KO) mice within a model of ovalbumin (OVA) -specific pulmonary inflammation. Upon OVA aerosol challenge, cell influx into the bronchoalveolar lavage (BAL) fluid consisted of neutrophils, macrophages and, more significantly, eosinophils - which are key effector cells in allergic inflammation. Each population was reduced by up to 80% in KO mice, demonstrating a role for PI3Kgamma in cell infiltration into the airways. The mechanism of reduced eosinophilia was analysed within both development and effector stages of the immune response. Comparable levels of OVA-specific T-cell proliferation and immunoglobulin production were established in both strains. Furthermore, no significant differences between WT and KO chemokine production were observed. Having identified the critical point of PI3Kgamma involvement, KO eosinophil chemotactic dysfunction was confirmed in vitro. These data are the first to demonstrate the vital role of PI3Kgamma in acute allergic inflammation. The profound dependency of eosinophils on PI3Kgamma for pulmonary influx identifies this lipid kinase as an attractive target for the pharmacological intervention of asthma.