4a,b) compared to OVA-SIT alone. To test whether these effects of CTLA-4–Ig on Treg persist after OVA inhalation challenges, the percentage

of CD4+CD25+FoxP3+ Treg cells were analysed in the blood 24 h after the last inhalation challenge. No significant differences in the percentage of CD4+CD25+FoxP3+ Treg cells were observed between the different treatment groups at this time-point (Fig. 4c). To further dissect the mechanism of the augmenting effects of CTLA-4–Ig on SIT we tested whether these effects are mediated by enhancing the activity of lung-resident Treg cells or Th1 cells which can suppress Th2 and effector cells upon allergen inhalation challenge. To this end we measured the levels of IL-10, TGF-β and IFN-γ selleck compound Buparlisib supplier in the lung tissue 24 h after the last OVA inhalation challenge. Remarkably, the levels of IFN-γ in lung tissue were reduced significantly in the group receiving combined CTLA-4–Ig and OVA-SIT compared to the group receiving only OVA-SIT (P < 0·05, Fig. 5c). No differences were observed in the levels of IL-10 and TGF-β in lung tissue between the different experimental groups (Fig. 5a,b).

In this study we demonstrate that CTLA-4–Ig acts as a potent adjuvant for SIT by strongly enhancing SIT-induced suppression of the manifestations of experimental allergic asthma, including Baricitinib the suppression of Th2 cytokine production, which was not achieved

by SIT treatment alone. The adjuvant effect of CTLA-4–Ig on SIT is independent of IDO activity, indicating that it is mediated by blocking the CD28-mediated T cell co-stimulatory signal. The tolerogenic effects of CTLA-4–Ig can be mediated by two mechanisms: (i) signalling into DC through B7 molecules, leading to activation of the non-canonical NF-κB pathway and induction of IDO [32] and (ii) blocking the CD-28-mediated co-stimulatory signal on T cells [12]. Here, we show that the adjuvant effect of CTLA-4–Ig on SIT is independent of IDO. In agreement with our observations, David et al. showed that CTLA-4–Ig inhibits DC-dependent proliferation of human T cells in vitro in an IDO-independent fashion [33]. In contrast, it has also been observed that administration of CTLA-4–Ig is tolerogenic in non-obese diabetic mice in a strictly IDO-dependent fashion [32]. However, as non-obese diabetic (NOD) mice show impaired expression of CTLA-4–Ig and develop autoinflammatory disorders spontaneously [32], these latter observations might not be relevant to our model, in which CTLA-4–Ig has been used in mice without such an impaired expression of CTLA-4. Moreover, IDO can only partially explain the CTLA-4-dependent regulation of T cell responses, as IDO-KO mice do not show the same lymphoproliferative phenotype as CTLA-4-KO mice [34].