Article
Extended Data Fig. 7 | Schematic summary of the f indings in this study. To p,
mNabs induced by commensal microbiota in dams were transferred to
neonates through the breast milk. Cross-reacting mNabs (especially IgG
antibodies) were detected that bound to the pathogenic, non-indigenous
bacterial species ETEC and correlated with protection against disease in pups
challenged with ETEC. IgG antibodies were also shown to be transported from
the milk to the bloodstream of pups by a process that we call IgG retro-
transport. Bottom, mNabs react with many commensal species and among
them an Enterobacteriaceae isolate (Pantoea) was found to induce antibodies
that cross-react with ETEC. The immunogenicity of this commensal species is
hypothesized to be a result of local antigen-sampling processes that involve
dendritic cells and uptake by Peyer’s patch germinal centres. This ultimately
leads to the induction of high-affinity IgGs directed against a Pantoea antigen
that cross-reacts with ETEC. IgG was also shown to be transported from the
blood stream to the intestinal lumen by FcRn in adult mice. Illustrations were
created with BioRender (https://biorender.com/).