The Biodiversity hypothesis of allergy: The interrelations between the skin microbiota, allergic diseases and exposure to microbes in residential environments

Jenni Maria Sofia Lehtimäki

    Forskningsoutput: AvhandlingDoktorsavhandling


    Biodiversity on earth is threatened and already drastically decreased due to anthropogenic actions. The ravenous utilization of natural resources has reached the point of payback in the forms of climate change, diseased crops, and disturbed water cycles. Obviously, these changes influence wellbeing of mankind. Besides these measurable problems, an invisible world, which covers all surfaces on earth, is altering. Loss of diversity in macroscopic organisms is repeated at the level of micro-organisms, many of which may have disappeared before ever described. The human body is a lively ecosystem hosting millions of microbial organisms, which together form the microbiota. These bacterial, viral, fungal, and other microscopic residents are faced with our immune system, challenging their survival. However, the relationship between the host and the residents is often not hostile, but in most cases reciprocal. Actually, the human immune system has partly shared the responsibility of immune-regulation with commensals. This evolved dependency between human and microbial residents highlights that several health problems may arise if this ancient collaboration is disturbed. Indeed, numerous inflammatory diseases coincide with disturbed host microbiota. These diseases, such as allergies, asthma, inflammatory bowel disease, and cancers, have increased rapidly since recent modernization of human habitats and lifestyle. Still, in traditional farming and hunter-gatherer communities allergies are almost absent. The biodiversity hypothesis, which is the concept tested in this thesis, suggest that change in the invisible world can seriously increase morbidity in human populations. This hypothesis states that the destruction of natural environments has altered our contact with microbial world, which can disturb our immune function, potentially leading to the development of inflammatory diseases. In this thesis, the emphasis is on the effect of exposure to environmental microbes, via the living environment and lifestyle, on health; central factors suggested by the biodiversity hypothesis. The key results from four separate projects, which are based on new datasets, are following. (I) Skin microbiota differs between rural and urban newborns and children. In teenagers this difference disappears, probably due to lifestyle-related changes. (II) Children who attend to nature-oriented outdoor-daycares have considerably more diverse skin microbiota than children in other daycares. However, their life differs in many ways from that of other children, indicating also the importance of lifestyle. (III) In the canine model, the prevalence of allergies is clearly lower in rural environments, also when the effect of dog-breed is controlled. Finally, (IV) the exposure to environmental microbes in residential environment, and through lifestyle, are concurrently related to the skin microbiota and allergies in the canine model. This thesis suggests the importance of living environment and lifestyle, which jointly influence the individual’s contact with environmental microbes, for health. Therefore, the human living environments, and the residing biodiversity in those, can either promote or disrupt human health. Currently, accumulating evidence projects that exposure to green environments, farms, children and animals, basically to all factors that increase microbial exposure directly or indirectly, are beneficial for human health. My thesis adds to this by showing interrelations between microbial exposure, microbiota and allergies. Therefore, people, especially children, and their fellow-animals, should increase their contact with diverse environments and lifeforms in order to support both microbial and immunological balance in their bodies. Finally, natural environments provide yet again one more invaluable ecosystem service, which should be recognized and protected.
    Tilldelande institution
    • Helsingfors universitet
    • Ruokolainen, Lasse, Handledare
    • Hanski, Ilkka Aulis, Handledare
    • Laatikainen, Tiina, Handledare, Extern person
    Tilldelningsdatum1 dec. 2017
    Tryckta ISBN978-951-51-3837-8
    Elektroniska ISBN978-951-51-3838-5
    StatusPublicerad - nov. 2017
    MoE-publikationstypG5 Doktorsavhandling (artikel)


    • 1181 Ekologi, evolutionsbiologi

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