The importance of metabolic activity in governing DC capability to mediate fungal allergic inflammation

Abstract

Constant exposure to Aspergillus fumigatus (Af) spores can cause allergic inflammation, leading to diseases such as asthma, which affects ~260 million people worldwide. A specific lung-resident dendritic cell (DC) subset (cDC2) is crucial for triggering allergic inflammatory responses, but the mechanisms that underpin this process are poorly understood. Bacterial ligands trigger dramatic shifts in DC glycolytic metabolism, which is essential for their capability to elicit effective immunity, but the metabolism of DCs in the lung is not well understood. Additionally, whether metabolic activity governs the ability of cDC2s to elicit downstream anti-Af allergic responses is unknown. To investigate how DC subsets respond to Af, we generated bone marrow-derived DCs with Flt3L (FLDCs, which recapitulate in vivo cDC subsets) and exposed them to spores. FL-cDC2s were the major responding subset, exhibiting increased expression of markers associated with DC activation (e.g. CD40, CD86) and migration (CCR7). Upon adoptive transfer into the airways of recipient mice, spore-pulsed FL-cDC2s were capable of migrating to the mediastinal lymph node and driving allergic inflammation. Using Seahorse and the recently developed flow cytometry-based SCENITH assay for measuring metabolism, we found changes in activation were accompanied by a rapid increase in glycolysis upon spore exposure. We then sought to explore metabolic changes in different lung DC subsets in a low-dose murine model of repeat Af exposure. This revealed limited changes in DC metabolism following spore exposure that appeared at odds with our FLDC data. We then investigated the possibility that few lung DCs were in direct contact with spores. Using fluorescently labelled Af, we ascertained that spore uptake by FL-cDC2s could increase activation and glycolysis. Tracking of spore uptake in lung DCs during allergic inflammation revealed preferential uptake by cDC2s, but < 1% of these cells acquired Af. SCENITH demonstrated that spore acquisition by cDC2s resulted in an increased glycolytic activity. To further investigate the role of glycolysis in the DC response to spores, we manipulated the metabolism of FLDCs. Blockade of glycolysis in FL-cDC2s prevented activation and limited spore uptake. FLDCs showed a dependence on nutrients that feed into glycolysis to support metabolism, with decreasing levels of glucose impairing FLDC activation in response to Af. This suggests that nutrient availability may be a rheostat that governs DC activation. In summary, this work demonstrates the crucial role of glycolytic metabolism in regulating the ability of DCs to mediate anti-fungal allergic inflammation in the airway.