Differential Response of Dendritic Cells and Macrophages to Signals from Airway Epithelial Cells in Humans: Changes with Age

Abstract

Abstract Advancing age significantly enhances the risk of respiratory diseases such as COPD, fibrosis etc. Immune response to respiratory viral infections is also impaired often leading to hospitalization. The underlying mechanisms are not well understood. Airway epithelial cells (AECs) and dendritic cells (DCs) and alveolar macrophages are the primary cells involved in respiratory immunity and tolerance. Since DCs and macrophages exist in close proximity to AECs, the function of both these cells is influenced by AECs. Using a 2D model to study the interaction of human primary bronchial epithelial cells (representative of AECs) with DCs we have recently demonstrated that AECs enhance the immune surveillance capacity of myeloid DCs (mDCs) from the circulation at homeostasis. Culture of mDCs with AECs resulted in the upregulation of pathogen recognition receptors (PRRs) and downstream signaling molecules. In contrast to circulatory mDCs, culture of macrophages with AECs led to a significant inhibition of LPS induced pro-inflammatory responses. More importantly, AECs induced the secretion of TGF-β and IL-10 from macrophages even in the absence of LPS stimulation. Thus, it seems AECs induce tolerance in macrophages but enhance the immunogenicity of mDCs suggesting a division of labor between DCs and macrophages in the respiratory mucosa. Investigation into the possible mechanisms for this differential response indicates that metabolites and growth factors from AECs may be responsible for inducing tolerance in macrophages and priming DCs. We also find that the crosstalk between AECs and macrophages and DCs is altered with age which may contribute to the increased susceptibility of elderly to respiratory diseases and infections. This study was supported by grant from the NIH AG045216 (to AA), and from the National Center for Research Resources and the National Center for Advancing Translational Sciences # UL1 TR000153.