5b). To evaluate the role of FcγRIIb on DCs in allergic airway inflammation, CD11c+ BMDCs were transferred into FcγRIIb-deficient mice. The effects of IVIgG on the increase of total cells and eosinophils in BALF, which MEK inhibitor were absent in FcγRIIb-deficient mice, were restored by transfer of WT CD11c+ BMDC (Fig. 6). CD11c+ BMDCs from FcγRIIb-deficient mice did not influence cell counts significantly in BALF from PBS- or IgG-administered mice. These findings suggest that the effects of IVIgG on allergic airway inflammation is largely dependent upon FcγRIIb of CD11c+ DCs.

Here we show for the first time that IgG and its Fc portion can act on inhibitory FcR expressed by DC to attenuate the local Th2 response and following allergic airway inflammation. We have shown the effects of IVIgG to reduce local Th2 cytokine production and subsequent development of eosinophilic

inflammation and AHR. These effects were clarified to be dependent upon FcγRIIb, the unique inhibitory FcR for IgG. Our data also demonstrated the inhibitory mechanism through FcRs on CD11c+ APCs in the pathogenesis of allergic airway inflammation. FcγRIIb expressed on immune cells regulates cellular behaviour, such as the proliferation of B cells, phagocytosis by macrophages and degranulation of mast cells [13,19]. In the present study, we focused upon the function of CD11c+ cells and showed that it was regulated negatively via FcγRIIb. Lung CD11c+ cells are APCs, including alveolar macrophages (AMs) and DCs. In the pathogenesis of asthma, CD11c+ CH5424802 DCs are especially potent APCs that have characteristics compatible with myeloid DCs and stimulate Th2 reactions, such as production of IL-4, IL-5, IL-13, resulting AHR and airway eosinophilia. Airway CD11c+ DCs reportedly induce Th2 cell stimulation

during ongoing airway inflammation [20]. Lambrecht et al. stated that a Th2 reaction and eosinophilic inflammation were diminished upon CD11c+ cell depletion, showing that CD11c+ myeloid DCs are necessary for the development and continuation of airway inflammation filipin by CD11c+ cells [21]. Meanwhile, pulmonary macrophages stimulate the naive T cell proliferation insufficiently and immunosuppress the APC function of lung DCs in situ[22]. These reports indicate that lung CD11c+ DCs play an important role in antigen presentation to induce a Th2 reaction and exacerbate allergic inflammation. Our results, using transferred BMDCs, emphasize that CD11c+ myeloid DCs play important roles among various types of cells involved in developing allergic inflammation. The effect of promoting Th2 reaction and inflammation was found to be regulated by FcγRIIb in the development of asthmatic features. Additionally, IVIgG exerts its effects on developed allergic inflammation even after OVA challenge, suggesting the therapeutic effects on airway inflammation.