Exposure to iron laden geogenic dust exacerbates the response to influenza infection

Aims: There are many communities around Australia that are exposed to high ambient concentrations of geogenic (earth derived) PM10 (<10 μm diameter particulate matter). There is anecdotal evidence that exposure to high concentrations of iron (Fe) laden PM10 has adverse health effects. We have shown previously that the concentration of Fe in community sampled geogenic PM10 is the primary determinant of the inflammatory and lung function response, however it is unclear how the concentration of Fe impacts on the response to a pre-existing infection. In this study we aimed to determine whether the concentration of Fe in community sampled geogenic PM10 impacts on the response to influenza infection.

Methods: The PM10 fraction was extracted from surface soil samples from four communities across Western Australia. BALB/c mice were intranasally exposed to 10 μg of PM10 (or saline) daily for 10 days. On the 6th day mice were exposed to influenza A (A/Mem/1/71) or a control preparation. 24 h after the last exposure we measured inflammation in the bronchoalveolar lavage (cells, MIP-2, IL-6, IFN-g), lung function and the responsiveness to methacholine (MCh).

Results: Both geogenic PM10 and influenza induced inflammation impaired lung function and increased the response to MCh. Co-exposure to particles exacerbated the response to influenza; particularly the influx of macrophages, the production of cytokines (IL-6 and IFN-g) and the response to MCh. After accounting for particle size and other metals the concentration of Fe was positively correlated with the number of macrophages (p = 0.04) and the maximum response to MCh (p = 0.01) and was negatively correlated with baseline airway resistance.

Conclusions: Collectively these data demonstrate that repeated low level exposure to geogenic PM10 exacerbates the response to a common respiratory infection. The magnitude of this response was altered by the concentration of Fe in the particles.