Highlights of IMMUNOLOGY2026™ - Invited Program Recordings-A seeding reaction to commensal microbes in human newborns

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Peter Brodin describes research on early-life immune development, focusing on a “seeding reaction” in the first week after birth. In a Swedish birth cohort, about half of term babies show a sharp, transient inflammatory cytokine response after birth, while others do not. This response could not be explained by basic metadata, but it was strongly associated with early colonization by Bacteroidea in the gut.<br /><br />Brodin argues that newborns are born with a leaky intestinal barrier, allowing microbial components to enter the bloodstream and trigger inflammation. He suggests this is an evolutionarily useful process that helps the immune system learn to tolerate and respond to the microbiome under protection from maternal antibodies.<br /><br />The seeding reaction appears to have lasting effects: it is linked to more mature innate immune responses, expanded CD4 memory T cells, greater IgG coating of commensal microbes, and changes in stem-cell programs. However, it may also increase later allergy risk, possibly because of excessive inflammatory responses to commensals. Brodin concludes that early microbial exposures likely shape lifelong immune health and may someday be modifiable through maternal or infant interventions, such as probiotics.

Keywords

early-life immune development

seeding reaction

newborn inflammation

Bacteroidea colonization

gut microbiome

maternal antibodies

allergy risk