Aspergillus fumigatus antigens activate innate immune cells via toll-like receptors 2 and 4

Invasive aspergillosis (IA) is a leading cause of mortality in haematological patients. Appropriate activation of the innate immune system is crucial for the successful clearance of IA. Therefore, we studied the Aspergillus fumigatus-mediated activation of human granulocytes and monocyte-derived immature dendritic cells (DCs), as well as murine bone marrow-derived DCs (BMDCs) from wild type, toll-like receptor (TLR)4-deficient, TLR2 knockout, and TLR2/TLR4 double deficient mice. Aspergillus fumigatus antigens induced the activation and maturation of immature DCs as characterized by CD83 expression, upregulation of major histocompatibility complex and co-stimulatory molecules. Moreover, fungal antigens enhanced the phagocytosis and production of interleukin (IL)-8 in granulocytes. The release of IL-12 by BMDCs in response to A. fumigatus antigens was dependent on the expression of TLR2, whereas the release of IL-6 was dependent on the expression of functional TLR4 molecules. The protein precipitate of A. fumigatus supernatant provided strong stimulation of DCs and granulocytes, indicating that a factor secreted by A. fumigatus might activate innate immune cells. In conclusion, A. fumigatus antigens induced the activation of DCs and granulocytes. Our results indicated that this activation was mediated via TLR2 and TLR4. Future studies are needed to assess the clinical impact of these findings in patients at high risk for IA.