The Living Microbiome

One cell thick: where the conversation happens

Microbes on one side, most of your baby's immune system on the other — separated by a single layer of cells, talking to each other all day long.

The microbial community In a breastfed infant, Bifidobacterium can be 90% of it fed by breast milk, then by food acetate butyrate lactate short-chain fatty acids The epithelial barrier one cell thick — and leakier in infants than in adults The lamina propria — the training ground ~70% of your baby's immune cells are down here, being taught Tregs teach tolerance Th17 cells coordinate defense ILC3s make IL-22, keep the lining intact IgA-producing B cells coat bacteria, keep them in check Macrophages sample and respond IL-22 signals back up
And the lessons don't stay in the gut
Lungs
gut bacteria in the first 100 days track with asthma risk
Skin
SCFAs strengthen the skin barrier against sensitization
Brain
~95% of serotonin is made in the gut; the vagus nerve listens
Whole body
trained immunity — reprogramming that lasts months to years
Schematic, not to scale. Pathways drawn from Fachi et al. 2025 (Cell Host & Microbe), Verhasselt 2024 (Immunological Reviews), Arrieta et al. 2015 (Sci Transl Med).
Growing Little Guts
Growing Little Guts by The Living Microbiome

Educational content only — not medical advice. Always consult your pediatrician.

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