An old adage says ‘we must all eat a peck of dirt before we die’, and there is increasing evidence linking the elimination of ‘dirt’ with a rising incidence of allergies and autoimmune disorders – the so-called ‘hygiene hypothesis’. More recently, a link between parasitic infections and the development of healthy immunoregulatory networks has been proposed.
There is evidence that worm infections in humans cause immunosuppression, and a team of scientists from the University of Nottingham has now shown a similar effect in populations of wild mice. Unlike laboratory animals, these mice were ‘naturally’ exposed to a variety of infections and so may provide a better insight into how the immune system functions in its natural context. The researchers used toll-like receptor (TLR) assays to provide an overall measure of immune function in response to a variety of parasites. After correcting for other variables, infection with both the nematode, H. polygyrus, and the louse, P. serrata, were found to suppress innate immunity, with a stronger effect produced by louse infections. It is perhaps surprising that the louse, just by attaching and feeding on the surface of the body can cause such a stronger immune response and the authors suggest that P. serrata could also secrete substances into the mouse that interfere directly with immune function or that the lice could act as a vector for an unidentified bacterial pathogen. The dampening of immune responsiveness associated with parasitic infections in wild mice supports the view that levels of innate immune activation in modern parasite-free human populations may be much greater than would have been typical during their recent evolutionary history, perhaps leading to an increased incidence of immune diseases.
The study is published in the journal BMC Biology.