Fig. 1.

Anticipated mechanisms of microbiota that could regulate vaccine effectiveness. A Pathogen-associated molecular patterns (PAMPs), such as LPS or peptidoglycan produced by microbiota, could be recognized by Pattern Recognition Receptors (PRR), such as TLRs and NOD2, expressed by immune cells. Signaling cascades activate transcription factors and induce gene expression, which could facilitate adjuvant effects to vaccines. B Microbiota-derived metabolites, such as SCFAs, could promote the differentiation of Th1 or Th17 cells and increase antibody production. C Epitopes from microbiota could cross-react with epitopes derived from target vaccine antigens