Regulating pulmonary macrophage responsiveness in a Th2 setting
Allergic airway inflammation is characterized by aberrant CD4+ T helper 2 (Th2) cell responses to inhaled allergens. These responses result in the production of Th2 cytokines IL-4, IL-5, and IL-13, mucus and IgE, accompanied by airway remodeling.
Resident macrophages (M?) have been shown to proliferate and ‘alternatively’ activate in situ in response to IL-4 across multiple tissue sites. However, it is not yet known whether IL-4 exerts this effect on pulmonary M?s. Further, the key molecular mechanisms that control proliferation and alternative activation of M?s in any tissue site are currently poorly understood.
To investigate the impact of Th2 inflammation on pulmonary M?s we used a reductionist approach, culturing ex vivo alveolar M?s with IL-4 in vitro or administering IL-4 complex (IL-4c) in vivo. Our data demonstrate that, unlike other tissue resident M?s, pulmonary M?s are poorly responsive to IL-4, most dramatically so in vivo. Together these data indicate a central role for the lung environment as a regulator of M? responsiveness to Th2 inflammatory signals in vivo. Comparing gene expression profiles of sorted alveolar M?s from control mice or those treated with IL-4c will help identify cell intrinsic factors and mechanisms that regulate alveolar M? proliferation and alternative activation. We intend to couple the data from the reductionist IL-4c model with an in vivo model of allergic pulmonary inflammation using the fungal allergen Aspergillus fumigatus. This work will provide novel insight into the fundamental mechanisms that control M?s during pulmonary inflammation, informing therapeutic targets for the treatment of chronic Type 2 inflammation.
Mechanisms of cross-talk between pulmonary epithelial cells and dendritic cells during Type 2 inflammation
The lung epithelium is today widely accepted as much more than just a physical barrier separating the air from the inner compartments of your body. It protects us from a never-ending exposure to potential threats and has the capacity to induce and direct an immune response if necessary. The type and severity of response is dependent on the type of stimuli encountered, and the immune status of the host.
With the establishment of in vitro cultures of two of the main cell types in the bronchial airways, epithelial cells (ECs) and dendritic cells (DCs), we can start to dissect the intricate interactions taking place in the early stages of an allergen exposure. House dust mite (HDM) and Aspergillus fumigatus are two common environmental allergens with the capacity to induce severe immune responses in predisposed or immunocompromised individuals. With the focus on healthy human subjects, we will try to understand the basal level of activity in fully differentiated bronchial ECs and monocyte-derived DCs, both separately and in a co-culture model. The data generated so far indicate a low but dose-dependent activation of moDCs in the presence of HDM or A. fumigatus. Interestingly, HDM induced a similar level of activation and co-stimulatory marker up-regulation to LPS, but much lower levels of secreted proteins, indicating a ‘muted’ response to HDM. Fully differentiated bronchial epithelial cells cultured in air-liquid interface responded to apical allergen treatment with reduced barrier integrity and an increased polarized secretion of inflammatory mediators. The next steps in this work will include further phenotypic and functional characterization of ECs and DCs responding to HDM or A. fumigatus. Together, this will increase our fundamental understanding of the key steps in initiation and direction of pulmonary allergic inflammatory responses.