In addition, we analysed pooled bLN fractions for T cell subsets without detecting any differences (data not shown). In summary, no significant differences were identified in CD4+, CD8+ and FoxP3+ Tregs in CD137−/− mice compared with WT mice; these results support our conclusion that CD137−/− mice show an equal Th2-mediated immune response. In our previous work we have shown that administration of an agonistic CD137 mAb inhibited the development of asthma and, moreover, MI-503 manufacturer was even capable of reversing established airway hyperreactivity (AHR), eosinophilic airway inflammation and production of allergen-specific

IgE in our murine asthma model [21]. Similarly, in a model of atopic conjunctivitis, stimulation of CD137 before or after sensitization inhibited the development of allergic disease [31]. Based on these findings, showing a strong effect of CD137 receptor stimulation in Th2 cell-mediated diseases, we expected

differences when we compared WT and CD137−/− mice in our asthma model. However, in contrast to our expectation, the absence of CD137 signalling did PF-01367338 in vitro not affect the development of allergic asthma; WT and CD137−/− mice developed comparably strong airway eosinophilic inflammation, mucus hypersecretion and enhanced OVA-specific serum IgE levels. The finding that CD137 stimulation via an agonistic mAb had significant effects on the manifestation of allergic parameters [21], whereas missing CD137 signalling did not affect the generation of an allergic phenotype in our model, is difficult to interpret. The potent effect of the CD137 agonistic mAb was associated with reduced production of Th2 cytokines, while secretion of IFN-γ was increased strongly. IFN-γ is one of the main inhibitors of Tacrolimus (FK506) Th2 cell development

and cytokine production which play a crucial role in the development and persistence of allergic asthma. Depletion of CD8+ T cells or blockade of IFN-γ partly abolished the protective effect of CD137 agonistic mAb treatment, indicating that this observation was mediated by IFN-γ-secreting CD8+ T cells [21]. This effect is absent in CD137−/− mice, which show comparable Th2 cytokine levels and CD4+ as well as CD8+ T cell frequencies compared to WT mice. In contrast to CD137 triggering the development of Th2 cytokine-producing cells is not affected in CD137−/− mice in our model, which might partly explain the missing difference between WT and CD137−/− mice in our allergic asthma model. Previous reports also show that lack of CD137 signalling does not mandatorily exert opposite results compared with stimulation of this receptor. For instance, treatment with CD137 agonistic mAbs has been shown to exert powerful anti-cancer effects in tumour models, while CD137−/− mice were remarkably resistant to tumour growth [5,7,11]. Follow-up studies demonstrated that CD137 signalling regulates the balance between CD8+ T cells and NK cells via modulation of IFN-γ production.