65 Inflammatory effects of Saharan dust in co-cultures: the role of microbial constituents

Abstract The exposure to Saharan dust (SD) is associated with increased respiratory morbidity and mortality. Previously we found the inflammatory properties of SD on macrophages to be mediated by the NLRP3 inflammasome pathway and downstream secretion of interleukin (IL)-1β. Heat-inactivation resulted in a strong reduction of its proinflammatory activity, suggesting that microbial constituents contribute to the inflammatory properties of SD. In the present study, we explored the role of microbial components in the inflammatory potency of SD. Based on an in-depth analysis of the microbial composition of SD during dust events, microbial mixtures composed of Gram-positive bacteria, Gram-negative bacteria, or fungi and a microbial cocktail containing all three mixtures, were prepared and gamma-irradiated before use. Co-cultures of A549 human lung epithelial cells and THP-1 macrophages were exposed to SD in the presence and absence of microbial mixtures in quasi-air-liquid interface (qALI) conditions. Heat-inactivation of SD abrogated the increased secretion of IL-1β. Furthermore, the cytokine-inducing effects of pristine SD could be restored upon addition of microbial mixtures to the heat-inactivated SD. A clear dose dependency of IL-1β secretion was observed in qALI co-cultures with both bacterial but not with fungi mixtures. At equal total microbial loads, exposure to Gram-positive or Gram-negative bacterial mixtures alone elicited stronger cytokine responses than exposure to the mixture of bacteria and fungi. The results of this work support the importance of microbial constituents, in the inflammatory effect of SD. Future experiments will focus on the investigation of Toll-like receptor signalling in SD exposed macrophages.