Children often catch colds, but some experience them far more frequently than expected. A deficiency in the antibody IgA may play a role. This antibody helps neutralize viruses. New research from Radboudumc, in collaboration with UMC Utrecht, shows that gut bacteria play a role in the immune defenses of children with recurrent respiratory infections and an IgA deficiency.
Children often catch colds. It is normal for children under the age of two to experience up to eleven respiratory tract infections per year. As they grow older, this number usually decreases. Still, even for children aged five to ten, six infections per year are not considered excessive. Usually, a virus is the culprit: the mucous membranes of the nose and throat become inflamed, swell, and produce extra mucus. This can lead to coughing, sneezing, or a sore throat.
Some children catch colds more often than expected. They suffer from recurrent respiratory infections. Roughly one in eight children is affected. The cause is not always clear, but in some cases, a problem with the immune system plays a role. About 40 percent of these children have a deficiency in the antibody IgA. This antibody helps identify and neutralize viruses. It primarily protects the mucous membranes, forming an important first line of defense against harmful pathogens.
According to pediatrician, infectious disease specialist, and immunologist Lilly Verhagen MD PhD from Radboudumc Amalia Children’s Hospital, treatment options for children with recurrent respiratory infections are limited. Sometimes doctors try to reduce symptoms, for example by prescribing daily antibiotics for an extended period. “But for many children, this is of little help,” says Verhagen. Moreover, antibiotics do not address the underlying cause. “That’s why we want to understand what causes an IgA deficiency, so that we can better treat children with this condition in the future.”
The researchers wondered whether gut bacteria might play a role in children with recurrent respiratory infections and an IgA deficiency. Gut bacteria are not only important for digestion, they also play a significant role in our immune system. To investigate this, the researchers examined the gut bacteria of 82 children under the age of seven with recurrent respiratory infections.
Dr. Mischa Koenen
The composition of gut bacteria in children with an IgA deficiency clearly differed from that of children with normal IgA levels. To better understand which bacteria influence IgA production, gut bacteria from several children were transferred to mice. One group of bacteria stood out: Bifidobacterium. “This is a well‑known ‘good’ gut bacterium,” explains physician‑researcher Mischa Koenen MD PhD from UMC Utrecht. When the researchers looked specifically at this bacterium in children with recurrent respiratory infections, they found that children with higher levels of Bifidobacterium in their intestines had fewer symptoms.
“It is promising that an immune deficiency might be influenced through gut bacteria,” says Verhagen. She now aims to investigate whether treatment with Bifidobacterium can improve IgA production in children and thereby reduce respiratory symptoms. “Hopefully, this will help us better support children with recurrent respiratory infections in the future.”
Would you like to learn more about respiratory infections in children? Listen to the podcast ‘Kind bij de dokter’ (in Dutch) in which Mischa Koenen explains more. If your child regularly experiences respiratory infections, discuss this with the treating physician or general practitioner.
Koenen MH, de Jonge MI, Hermsen M, van Weelden GH, Olde Olthof S, van der Gaast-de Jongh CE, van Opzeeland F, de Kluijs-Bender C, van Selm S, van der Vries E, Bogaert D, Boes M, de Zoete MR, Verhagen LM. Bifidobacterium-driven immunoglobulin A production in pediatric patients with IgA deficiency and recurrent respiratory infections. Microbiome 2026;14:137.
