Australian researchers have discovered an "immune signature" in the cord blood of children with clinical signs of food allergies at 12 months, they report in the journal Science Translational Medicine.
While it cannot be proven the heightened immune response at birth caused the food allergies, it "clearly differentiated these children from the rest," said one of the study's authors, Professor Len Harrison of the Walter and Eliza Hall Institute.
"This study really emphasises how critical it is to look at pregnancy and early life to really understand why chronic immune and inflammatory disorders such as allergies develop in childhood and later," Professor Harrison said.
Recent decades have seen a rise in childhood food allergies, with most of the increase seen in children under the age of five.
To help understand why this is occurring, Professor Harrison and colleague Dr Yuxia Zhang teamed up with paediatrician Associate Professor Peter Vuillermin of Deakin University and the Murdoch Childrens Research Institute, who heads up a study of pregnant mothers and babies in the Barwon region of Victoria.
The Barwon study follows the mothers and their children over time, identifying those with allergies.
"We asked the question: Is there anything abnormal about the immune systems of these children at birth or soon after birth?" Professor Harrison said.
The researchers discovered that the immune system's "foot soldier" cells, called monocytes, were activated in the cord blood of children at high risk of developing food allergies. Signals from these activated cells then drive another type of immune cell called T-cells, which are involved in inflammation and allergies.
"All this is happening in the cord blood and setting up these children for a very high risk of allergy within the year," Professor Harrison explained.
Hunt to discover what causes inflammation at birth
Professor Harrison said the discovery could have implications for the development of a screening test for children at risk, "but the most important thing is to figure out what causes this and to change those circumstances".
"I think the likelihood of a [genetically inherited abnormality] being the sole cause of this phenomenon is low," he said.
"I think it is more likely to be acquired somehow.
"One of the reasons for that is that the incidence of food allergy has increased considerably in the last 20 or 30 years or so, and really that can only be due to environment."
The researchers found the duration of the mother's labour played a role in the immune response.
"There was a relationship between these changes in the immune cells in the cord blood and the duration of labour … but there wasn't a significant relationship between duration of labour and food allergy itself."
However, he said, inflammation caused by prolonged labour may "prime" the immune system of some children to respond to subsequent events in the first year of life.
Researchers are also investigating whether other environmental factors, such as infection of the placenta or amniotic fluid, the influence of the mother or baby's gut microbiome, or the nutritional status of the mother may play a role.
"For example, Vitamin D deficiency has been associated with allergy in infants," Professor Harrison said.
"We're looking to see if the children who have this signature at birth or their mothers have lower levels of Vitamin D. At the moment we can't find that. That's one of the things that's just been ticked off the list."