5a) or bLNs (data not shown) of OVA-sensitized and challenged WT or CD137−/− mice showed equally enhanced proliferation, while lymphocytes isolated from controls proliferated only slightly. In addition, we determined cytokine production in supernatants of lymphocyte cell cultures by ELISA. Th2 cytokines IL-5 and IL-13 were increased markedly in cell cultures

of both OVA-immunized CD137−/− and WT mice compared to controls (**P ≤ 0·01) (Fig. 5b), but no significant differences were observed between IL-5 and IL-13 production in spleen cell cultures derived from CD137−/−versus WT mice that underwent the allergy protocol. Th2 cytokine IL-4 and IFN-γ, as signs of the Th1 response, were very low (<50 pg/ml) to undetectable (data not shown). As demonstrated above, we observed similar allergic parameters in CD137−/− and WT mice after OVA sensitization and challenge, demonstrating that CD137 is

R788 not required for the development of a Th2-dominated allergic phenotype. Furthermore, we were interested in whether CD137 co-stimulation Metformin is involved in respiratory tolerance induction. Hence, mice were tolerized via mucosal application of OVA before sensitization (Fig. 1, tolerance protocol). Consistent with previous studies [28,30], tolerized WT mice (WT TOL) showed reduced signs of allergic airway disease and resembled the control group (WT Alum). CD137−/− mice were equally protected: we did not detect any significant differences Florfenicol with regard to total BALF cell count and eosinophilia (Fig. 2b,c) or pulmonary inflammation and mucus production (Fig. 3). Furthermore OVA-specific IgE, IgG1 and IgG2a serum levels (Fig. 4), in vitro proliferation and Th2 cytokine production were equivalent (Fig. 5a,b). To summarize, all measured parameters were comparable

in tolerized wild-type and CD137−/− mice, suggesting that loss of CD137 is not critical for respiratory tolerance induction in our model. We determined T cell subsets via flow cytometry in spleen and lungs from individual WT and CD137−/− mice on day 21 of the immunization protocols (Fig. 1). Similarly, we found significantly elevated percentages and numbers of CD4+ T cells in lung of OVA-immunized WT and CD137−/− mice (Fig. 6b); in parallel, we observed a slight trend towards reduced proportions of splenic CD4+ T cells after sensitization and challenge (Fig. 6a). With regard to CD8+ T cell frequency, we detected no significant differences after immunization. Again, CD137−/− mice had comparable percentages and absolute numbers in spleen and lung to the WT groups independent of the immunization protocol used. Analysis of Treg (CD4+FoxP3+) cells revealed significantly enhanced percentages in lung (Fig. 6b) of both OVA-immunized mice strains, whereas we did not observe this increase in spleen (Fig. 6a).