Modulatory effects of divalent mercury and lead on the immune responses of waterfowl upon a viral-like immune challenge

Summary

Trace metals, such as mercury (Hg) and lead (Pb), have been reported to be immunotoxic to animals, however, relatively little is known about their effects and modes of action for avian species, especially waterfowl, which are frequently linked to the transmission of avian influenza infections. Given the fact that wild waterfowl are natural reservoirs for avian influenza viruses, impaired immune competence and pathogen resistance due to trace metal exposure in wild waterfowl may raise the risks of infections and might result in avian influenza outbreaks. Therefore, it is crucial to investigate the modulatory effects of trace metals, namely Hg(II) and Pb(II) in this thesis, on the immune responses of waterfowl. The objective of this thesis was to investigate whether realistic environmental levels of Hg(II) and Pb(II) exposure could modulate the immune responses in waterfowl upon a viral-like immune challenge and to explore the underlying modes of action. With the stepwise approach, we were able to compare the effects of Hg(II) and Pb(II) in the field study with the controlled in vivo and in vitro studies. The major effects of Hg(II) and Pb(II) were promoting inflammation and impairing B-lymphocyte functions upon a viral-like immune challenge. This disturbance of the avian immune system potentially hampers the immune response upon viral infections, which might cause a higher risk of infection for individuals and even prevalence of diseases in the population as a whole. Altogether, this thesis indicates that even at low environmentally relevant levels, Hg(II) and Pb(II) exposure affected the immune responses in waterfowl upon a viral-like immune challenge, mainly by promoting inflammation and impairing B-cell functions. The current study emphasises the potential need to include immunomodulatory effects on birds in the environmental risk assessment of chemicals. This is relevant not only for the protection of wildlife populations, but also towards sustaining environmental and human health.