TLR9 is Actively Recruited to Aspergillus fumigatus Phagosomes and Requires the N-terminal Proteolytic Cleavage Domain for Proper Intracellular Trafficking1

• Published in: The Journal of immunology (1950) 2010-11, Vol.185 (12), p.7614-7622
• Main Authors: Kasperkovitz, Pia V., Cardenas, Michael L., Vyas, Jatin M.
• Format: Article
• Language: English
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.1002760

Toll-like receptor 9 (TLR9) recognizes unmethylated CpG DNA and induces innate immune responses. TLR9 activation is a multistep process requiring proteolytic cleavage and trafficking to endolysosomal compartments for ligand-induced signaling. However, the rules that govern the dynamic subcellular trafficking for TLR9 after pathogen uptake have not been established. In this study, we demonstrate that uptake of Aspergillus fumigatus (Af) conidia induced drastic spatial redistribution of TLR9 to the phagosomal membrane of Af -containing phagosomes but not to bead-containing phagosomes in murine macrophages. Specific TLR9 recruitment to the fungal phagosome was consistent using Af spores at different germination stages and selected mutants affecting the display of antigens on the fungal cell surface. Spatiotemporal regulation of TLR9 compartmentalization to the Af phagosome was independent of TLR2, TLR4 and downstream TLR signaling. Our data demonstrate that the TLR9 N-terminal proteolytic cleavage domain was critical for successful intracellular trafficking and accumulation of TLR9 in CpG-containing compartments and Af -phagosomal membranes. Our study provides evidence for a model in which Af spore phagocytosis by macrophages specifically induces TLR9 recruitment to Af phagosomes and may thereby mediate TLR9-induced antifungal innate immune responses.