Children raised in rural environments, spending time outdoors in the sun and being exposed to farm animals grow up to have better-regulated immune systems and fewer allergies than their city counterparts.
The finding is based on research by the University of Cape Town’s (UCT) division of paediatric dermatology and paediatric allergy which examined how environmental exposure influenced inflammatory response in children.
Using medical tests known as RNA sequencing, of peripheral blood mononuclear cells (PBMCs) to study immune cell behaviour, they analysed molecular profiles of children with atopic dermatitis (eczema) as opposed to healthy controls from the same ethnolinguistic population in Cape Town and Mthatha.
The skin disorder disproportionately affects children globally and is associated with multiple allergic diseases. Analysis demonstrated several differentially expressed genes in eczema cases, including IgE, a key antibody isotype in allergic disease. Researchers found that the living environment influenced children’s immune development.
Exposure to pets, farm animals, being born through vaginal delivery, as well as sunlight exposure were some of the associated exposures with a rural childhood. Peanut and sour milk consumption, higher household income, and increased paracetamol use were more strongly associated with urban living exposures.
Exposure to animals and time spent outdoors promotes immune regulatory networks that can protect against infection and immune-mediated diseases such as allergies
— Dr Nonhlanhla Lunjani
Researchers found that the immune systems of children living in rural areas had several ways to deal with threats. Gene expression pathways that suppressed abnormal inflammatory immune response were demonstrated more in rural children compared with their urban counterparts.
Writing in the European Journal of Allergy and Clinical Immunology, researchers said the latest findings supported a body of evidence suggesting exposure to certain environmental and lifestyle factors during childhood could have significant consequences, even later in life.
The study's lead author Dr Nonhlanhla Lunjani said these interactions ideally should promote appropriate immune training that effectively defends against infection and tolerates otherwise harmless allergen exposures. An immune system must learn not to over-respond in early life to avoid excessive reactions in later life that can lead to disease.
Lunjani said the findings illustrated the dramatic effect of the living environment on developing an infant's immune system.
“Exposure to animals and time spent outdoors promotes immune regulatory networks that can protect against infection and immune-mediated diseases such as allergies.
“Understanding the environmental interactions and molecular switches responsible for developing a healthy immune system will help us develop public health interventions and provide appropriate guidance to mothers of young children,” she said.
Lunjani said epidemiology studies had shown allergic diseases were increasing rapidly in South Africa but there was a lower prevalence in rural communities.
Previous work done by UCT demonstrated allergic immune profiles in urban and rural children with eczema compared with their healthy counterparts. “However, an immune profile emerged that characterised rural vs urban living irrespective of disease state,” she said.
“Our current study aimed to further examine the molecular mechanisms and environment exposures underpinning the rural and urban immunological gradient in South African children with or without atopic dermatitis.”
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