Peanuts, milk, eggs, and shellfish are among the most common food allergens. | Jack Dykinga/ USDA ARS
Babies who develop food allergies display hyperactive immune responses at birth, according to a study of about 1000 infants published in the 13 January issue of Science Translational Medicine. The findings help unravel the mechanisms underlying early development of food allergies and hint that anti-inflammatory approaches may help infants avoid the disease.
"What is most important is the finding that our immune system is poised at birth for disease risk later in life," said Yuxia Zhang of the University of Melbourne, Australia, who is first author of the study. The enhanced inflammatory responses among food-allergic infants "provide a signature to examine what and how pre- and post-natal environmental factors and genetic background may determine individuals' risk for disease development," she said.
"Future studies [are needed] to understand why some babies are born with increased innate immune responsiveness, and ultimately, what can be done to prevent this," said senior author Peter Vuillermin, also from the University of Melbourne.
Food allergy is an abnormal immune response to certain foods — most commonly peanuts, milk, and shellfish — that can range from mild to deadly. It is becoming increasingly common, more so in children than adults, in both developed and developing countries. According to the Centers for Disease Control and Prevention, the number of children in the United States reported to have a food allergy in the previous 12 months jumped from 3 million in 2007 to 4.1 million in 2012.
Babies who develop food allergies are known to share a pro-inflammatory innate immune system — the body's first line of defense against foreign invaders — but the exact immune changes that trigger food allergies are poorly understood.
Analyzing immune cells in umbilical cord blood from 1074 infants, Zhang and colleagues found that babies who showed hyperactive innate immune responses at birth went on to develop a food allergy when tested at age one.
Compared to their non-allergic peers, infants who developed a food allergy had greater amounts of innate immune cells called monocytes and reduced amounts of immune-suppressive T cells, known as natural regulatory T cells. T cells, along with B cells and others, comprise the adaptive arm of the immune system, the body's second line of defense which quickly attacks and "remembers" specific pathogens.
Monocytes from food-allergic infants released more inflammatory signaling molecules that curbed production of a molecule critical to maintaining natural regulatory T cells. This inflammatory environment drove both natural regulatory T cells and another type of T cell to develop into T helper 2 (T H2) cells, which are known to trigger inflammation during allergic reactions.
"An exaggerated inflammatory response among cellular elements of the innate immune system can drive the adaptive immune system down an allergy-associated T H2 pathway," said Vuillermin. "We now have an exciting opportunity to understand the underlying basis and antecedents of this profile."
The researchers say that both genetic and environmental factors might be involved in steering the immune system into adopting this pro-inflammatory, allergic profile.
For instance, growing evidence pinpoints the crucial role of the gut microbiome, the collection of bacteria that colonize our intestine, in shaping the immune system. "We are particularly interested in the potential role of the mother's microbiome and its metabolites during pregnancy," said Vuillermin.
Previous studies have also revealed a potential link between consuming food with anti-inflammatory properties — such as those rich in omega‑3 fatty acids, fiber, or certain essential vitamins — and lower risk of developing a food allergy. "I think mother's diet during pregnancy and lactation maybe a good place to start as a possible preventative strategy," said Zhang.