Mothers tailor sons' immune systems to suit environment, study shows
When pregnant mice feel threatened by disease, they tend to produce sons who are less aggressive but have more efficient immune systems than mice whose mothers were not threatened with infection during pregnancy, according to new research from the University of Nottingham in the UK. The findings, published in the Proceedings of the Royal Society B, offer the first evidence for environmental cues having a transgenerational effect on immune response, with the mother's perception of disease risk determining her offspring's ability to fight off infection. The study sheds new light on the factors behind individual disease susceptibility, and also has implications for the design of experiments involving animals. Many animals, including mice and humans, are able to detect disease in others. Odour is a particularly strong indicator of infection, and physicians have long used smell to diagnose diseases in humans; typhoid is characterised by a baked bread odour, while sufferers of yellow fever often give off a distinctive meaty odour, for example. Furthermore, researchers have previously found that direct infection of pregnant animals has an impact on the immune system of their offspring. In this study, the researchers hoped to find out whether the mere presence of diseased individuals in a pregnant mouse's environment would have immunological consequences for her offspring. The researchers housed pregnant mice next to male mice that had been infected with Babesia microti, a mild blood parasite. The pregnant mice could see, hear and smell their infected neighbours but could not touch them. The pregnant mice could not be infected with the parasite, as transmission is only possible through a tick (which was not present in the laboratory) or direct exchange of blood (which was not possible as the animals could not touch). Another group of pregnant mice was housed next to healthy males. The scientists found that the females housed next to infected males had higher levels of the stress hormone corticosterone in their blood. Corticosterone is known to affect foetal development. Meanwhile the offspring of these mothers were significantly less aggressive than the offspring of the control group. However, when infected with B. microti, they fought off the parasite much more effectively than the control group's offspring. These findings support previous research that identifies a trade-off between aggression and immune response in male mice. In adult mice, aggression is linked to social dominance, territorial acquisition and increased mating opportunities. However, aggressive behaviour appears to be offset by reduced resistance to disease. In an environment where the risk of disease is high, mice that are able to fight off infection quickly will be at an advantage over mice whose immune systems are weaker. 'It seems that the mothers in our study are priming offspring for the environment they will live in,' explains the University of Nottingham's Dr Olivia Curno, who led the research. 'When the risk of disease is high, improved immunity may outweigh any costs associated with reduced social dominance.' The researchers also warn that their findings have implications for the design of experiments involving animals. In most animal housing units, different groups can see, hear and smell each other. 'We have shown that a measurable perception of disease in neighbouring conspecifics occurs, and elicits a stress response in the perceiver,' the scientists write. 'Therefore, our results highlight the potential for substantial and unexpected effects of experimental design on animal welfare.' The scientists also question the validity of considering 'control' animals as 'untreated', as these latest findings suggest that they could respond physiologically and behaviourally to cues from their treated neighbours. 'It is unlikely that mice are the only species with this fascinating ability,' commented Dr Curno. 'Therefore our work may have important implications for our understanding of epidemiological processes and individual disease susceptibility in general. Future investigation should explore exactly how the females detect the disease in their neighbours and use this information so cleverly.'
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