IMMUNOLOGY2026™ Conference Recordings For Attendees-A seeding reaction to commensal microbes in human newborns

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Peter Brodin opened a symposium on early life immune development by describing his lab’s work on how newborns adapt their immune systems after birth. Using the Stockholm Born Immune Cohort and additional cohorts, his team found a transient “seeding reaction” in about half of term infants during the first week of life: a strong systemic inflammatory cytokine response linked to exposure to colonizing microbes. This reaction was not explained by basic metadata, but was associated with abundant Bacteroides in stool, leaky gut barrier function, and microbial components detectable in plasma after birth.<br /><br />Brodin proposed that this early leakage may be evolutionarily useful, allowing the infant immune system to sense its microbiome under protection from maternal antibodies. Strong seeding reactions were linked to accelerated innate immune maturation, expanded memory CD4 T cells, more clonal T-cell responses, increased IgG coating of commensal microbes, and broader inflammatory signals in stool. However, they were also associated with higher later allergy risk and increased IgE responses.<br /><br />He presented in vitro systems using cord blood and stem cells to model this process and suggested that early microbial priming may imprint long-term immune outcomes. He concluded that while the reaction may be adaptive in evolution, it could be maladaptive in modern settings and might be a target for early-life interventions.

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Date April 16, 2026 8:00 AM - 8:33 AM

Room 253

Session Major Symposium A: Early Life Immune Development and Function

Speaker Petter Brodin

Track Hematopoiesis and Immune System Development (HEM)

Year 2026

Keywords

newborn immune development

seeding reaction

microbiome colonization

Bacteroides

innate immune maturation

allergy risk

early-life immune priming

April 16, 2026 8:00 AM - 8:33 AM

253

Major Symposium A: Early Life Immune Development and Function

Petter Brodin

Hematopoiesis and Immune System Development (HEM)

2026