Radiation-Detoxified Form of Endotoxin Effectively Activates Th1 Responses and Attenuates Ragweed-Induced Th2-Type Airway Inflammation in Mice

Urbanization with reduced microbial exposure is associated with an increased burden of asthma and atopic symptoms. Conversely, environmental exposure to endotoxins in childhood can protect against the development of allergies. Our study aimed to investigate whether the renaturation of the indoor environment with aerosolized radiation-detoxified lipopolysaccharide (RD-LPS) has a preventative effect against the development of ragweed-induced Th2-type airway inflammation. To explore this, cages of six-week-old BALB/c mice were treated daily with aerosolized native LPS (N-LPS) or RD-LPS. After a 10-week treatment period, mice were sensitized and challenged with ragweed pollen extract, and inflammatory cell infiltration into the airways was observed. As dendritic cells (DCs) play a crucial role in the polarization of T-cell responses, in our in vitro experiments, the effects of N-LPS and RD-LPS were compared on human monocyte-derived DCs (moDCs). Mice in RD-LPS-rich milieu developed significantly less allergic airway inflammation than mice in N-LPS-rich or common environments. The results of our in vitro experiments demonstrate that RD-LPS-exposed moDCs have a higher Th1-polarizing capacity than moDCs exposed to N-LPS. Consequently, we suppose that the aerosolized, non-toxic RD-LPS applied in early life for the renaturation of urban indoors may be suitable for the prevention of Th2-mediated allergies in childhood.

The epigenetic state of IL-4-polarized macrophages enables inflammatory cistromic expansion and extended synergistic response to TLR ligands

Prior exposure to microenvironmental signals could fundamentally change the response of macrophages to subsequent stimuli. It is believed that T helper-2 (Th2)-cell-type cytokine interleukin-4 (IL-4) and Toll-like receptor (TLR) ligand-activated transcriptional programs mutually antagonize each other, and no remarkable convergence has been identified between them. In contrast, here, we show that IL-4-polarized macrophages established a hyperinflammatory gene expression program upon lipopolysaccharide (LPS) exposure. This phenomenon, which we termed extended synergy, was supported by IL-4-directed epigenomic remodeling, LPS-activated NF-κB-p65 cistrome expansion, and increased enhancer activity. The EGR2 transcription factor contributed to the extended synergy in a macrophage-subtype-specific manner. Consequently, the previously alternatively polarized macrophages produced increased amounts of immune-modulatory factors both in vitro and in vivo in a murine Th2 cell-type airway inflammation model upon LPS exposure. Our findings establish that IL-4-induced epigenetic reprogramming is responsible for the development of inflammatory hyperresponsiveness to TLR activation and contributes to lung pathologies.