Accumulation of pulmonary vacuolated eosinophils in experimental allergic asthma that synergize with dendritic cells to induce Th-17 cells

Eosinophils are considered a homogenous cell population, contributing to the allergic asthma phenotype by promoting mucus hypersecretion and airway hyperresponsiveness. Here, we identified a previously unrecognized vacuolated CD11c dim eosinophilic population (vEOS) which accmulates exclusively in the lung tissue and in mediastinal lymph nodes but not in the airways in a house dust mite-mediated allergic asthma model and an IL-33 mediated pulmonary inflammation. In addition to the vEOS, we found classical SiglecF + CD11c − eosinophils (EOS) in the airways and the lung. Both cell types shared typical structural features of eosinophils and expressed CCR3. In contrast to EOS, vEOS expressed higher levels of the CD11a, CD11b and CD18 integrins. Immunofluorescence microscopy revealed that vEOS were located exclusively near arteries and airways, where they were in close contact with T cells. Moreover, vEOS took up antigen and expressed costimulatory molecules more efficiently than EOS. Consequently, in co-culture experiments with OVA-TCR transgenic T cells, vEOS and dendritic cells (DCs) drove T cell proliferation. However, in the presence of vEOS, T cells divided more frequently than in co-culture with DCs. Further, T cell activation in response to co-culture with vEOS together with DCs markedly enhanced IL-17 but not IL-13 production. Collectively, our data demonstrate that vEOS are an important subset of eosinophils, which differ from EOS in their location and their ability to activate T cells. Further, they suggest that cross-talk between vEOS and DCs might be a crucial step for the induction of Th17 cells in allergic asthma. Thus, vEOS may serve as an important target for Th17-associated steroid-resistant asthma.