Children with IgA deficiency and recurrent respiratory tract infections harbour a distinctly altered intestinal microbiota, and a Bifidobacterium-dominated community cluster was linked to stronger IgA responses in stool, serum, and lung, highlighting a microbiota-mucosal immunity axis with translational potential.
IgA deficiency was present in 38% of children under 7 years with recurrent respiratory tract infections (rRTIs), indicating a high prevalence in this clinical population.
The gut microbiota composition of IgA-deficient children with rRTIs differed significantly from that of symptomatic non-IgA-deficient children.
Transfer of pediatric fecal microbiota into germ-free mice induced strong increases in serum and fecal IgA levels.
Two distinct microbial community clusters were associated with fecal IgA induction in germ-free mice, one of which was a Bifidobacterium-dominated cluster consisting of eight bacterial genera.
In children with rRTIs, Bifidobacterium abundance was negatively associated with the severity of respiratory tract infection symptoms.
The Bifidobacterium-dominated community cluster was linked to stronger IgA responses across multiple mucosal sites including stool, serum, and lung in the germ-free mouse model.
This research suggests that a surprisingly high proportion of young children who suffer from frequent respiratory infections — nearly 4 in 10 — have a condition called IgA deficiency, meaning their bodies do not produce enough of the antibody immunoglobulin A, which is critical for defending mucosal surfaces like the lungs and gut. The study also found that these IgA-deficient children have a noticeably different mix of bacteria in their intestines compared to children who have similar respiratory problems but normal IgA levels, suggesting the gut microbiome may play a role in whether a child produces adequate amounts of this protective antibody. To test this idea more directly, the researchers transplanted gut bacteria from these children into germ-free mice (mice raised with no bacteria of their own). Mice that received the human gut bacteria developed robust IgA responses in multiple body locations — in their stool, blood, and lungs. Notably, mice that received bacteria dominated by a group called Bifidobacterium showed the strongest IgA responses and had more immune B-cells in their lungs. Back in the children themselves, having more Bifidobacterium in the gut was also linked to less severe respiratory infection symptoms. This research suggests that the balance of bacteria in a child's gut may influence how well their immune system produces IgA, and that interventions aimed at promoting Bifidobacterium — such as through diet or probiotics — could potentially help children prone to frequent respiratory infections. While this is still early-stage research requiring further clinical investigation, it points toward a meaningful connection between gut bacteria and respiratory immune defense in young children.
Koenen M, de Jonge M, Hermsen M, van Weelden G, Olde Olthof S, van der Gaast-de Jongh C, et al.. (2026). Bifidobacterium-driven immunoglobulin A production in pediatric patients with IgA deficiency and recurrent respiratory tract infections.. Microbiome. https://doi.org/10.1186/s40168-026-02382-0