Toll like receptor 5 (TLR5) may be involved in the immunological response to Aspergillus fumigatus in vitro.

Toll-like receptors (TLRs) are involved in the host defense against Aspergillus fumigatus infections, and some TLRs may even be exploited by the mould to escape immune mechanisms. We have previously shown that conidia from A. fumigatus increase expression of TLR5 in human monocytes. When further investigating a possible role of TLR5 in A. fumigatus infections, we observed a decrease in conidial viability after culturing with TLR5-knockdown THP-1 monocytes. Secondly, our experiments showed an increase in conidial viability when THP-1 monocytes, together with flagellin, are cultured with conidia. Thirdly, we found that treatment of THP-1 monocytes with a monoclonal antibody against TLR5 resulted in increased conidial viability after culturing. Experiments with a HEK-293 cell line only expressing TLR5 did not indicate that conidia directly interact with TLR5. Further studies of the intracellular molecular mechanisms activated concomitant with activation of TLR5 that have an enhancing effect on the viability of conidia may shed new light on the defense against conidia in monocytic cells, and possibly also on the function of the TLR5 system.