To study the interaction of airway epithelial cell line A549 with fragments of mycelium, spores of Aspergillus fumigatus in vitro and to determine if toll-like receptors (TLRs) are involved in the process.

A549 cells were exposed to fragments of A. fumigatus mycelium, zymosan and inactivated A. fumigatus spores. Interleukin 6 (IL-6) and IL-8 released by A549 cells to the culture supernatant were measured by ELISA. Presence of TLR2 and TLR4 on A549 cells were studied by immuno-histochemisty.

Mycelium fragments of A. fumigatus showed strong binding to epithelial cells but had limited effects on the release of IL-6 and IL-8 by A549 cells. Irradiated A. fumigatus spores were partly internalised by A549 cells and inhibited A549 cells to produce IL-6. TNF-⍺ pre-incubated A549 cells produced increased IL-6 after exposure to zymosan and WIAF. Immuno-histochemistry showed a negative staining for TLR2 and TLR4.

The low levels of cytokines produced by A549 cells after the firm binding of either mycelium or spores of A. fumigatus may lead to insufficient recruitment of inflammatory cells to the infected site, which may result in the escape of detection by the immune defence system. TLR2 and TLR4 are probably not or only in part involved in the above process, although very low expression cannot be excluded.