TLR2 and asthma: Maternal enteric microbes also ferment dietary fibers to the short-chain fatty acid (SCFA) acetate, that suppresses allergic airway disease, a mouse model for human asthma, by enhancing Treg cell numbers and function in adult offspring.40 In the context of a maternal infection, bacterial peptidoglycan, which is a ligand for Toll-like Receptor 2 (TLR2), traversed the placenta to influence fetal neuro-proliferation.41 Passage of other microbial TLR ligands across the placenta that influence fetal immune development remains a formal possibility.