Finally, FcR γ-chain-deficient mice are devoid of FcεRI and therefore any FcεRI-mediated effects of OVA-specific IgE during the sensitization or challenge phase, either due to mast-cell activation or altered DC function, is absent in these mice. Although the sensitization/challenge model that we used does not require B cells or antibodies, including
allergen-specific IgE, FcεRI, or mast cells 21, 22, it remains possible that in vivo FcεRI facilitated enhanced antigen-uptake or activation of pulmonary DC indirectly through mast-cell activation 23, 24. In contrast to previous studies 13, 14, 17 that employed BMDC and sensitization of FcγR-deficient mice, we aimed to specifically delineate the contribution Sirolimus of FcγR on lung DC during the challenge phase of the murine asthma model. We first confirmed the expression of FcγR expression on lung DC and compared their function to spleen-derived DC subpopulations, as the importance of considering the phenotypic, functional and anatomical differences of various DC subsets has been supported by several studies 25. Thus, our studies
focus on check details DC populations obtained from lymphoid organs in addition to pulmonary DC to study the function of FcγR. This revealed that lung DC and splenic CD8− DC gave rise to increased CD4+ T lymphocyte stimulation when DC acquired antigen as immune complexes via FcγRI, FcγRIII or FcγRIV. This effect was absent when CD8+ DC or FcR γ-chain deficient DC were used. These observations would be consistent with the view that contamination Interleukin-2 receptor of OVA with endotoxins was not responsible for these alterations. Additional results support this interpretation. First, DC of TLR4-deficient mice led to increased T-cell proliferation after exposure to OVA-IC as compared to OVA alone. Second, serum of sensitized mice, which contained anti-OVA IgG, caused increased T-cell proliferation when given together with OVA to WT lung DC. This effect was antigen-specific, as serum of BSA-sensitized
mice did not cause this outcome, and FcγR-dependent, given that FcR γ-deficient DC did not result in increased T-cell proliferation. Several observations support the impact of FcγR on DC during the effector phase of pulmonary hypersensitivity. First, we adoptively transferred Th2-biased antigen-specific CD4+T lymphocytes 4 into antigen-naïve mice, thereby restricting the induction of pulmonary hypersensitivity mainly to the DC–T-cell interaction. Second, pulmonary exposure of mice to OVA-IC dramatically increased eosinophilia in the BALF and cellular infiltration in the lungs, an effect that was not observed in naive mice and thus not induced non-specifically. Third, the increased pulmonary immune reaction induced by OVA-IC was paralleled by a highly significant increase in proliferation of antigen-specific T cells, both in vitro as well as in vivo.