AUTHOR=Elkjaer Maria L. , Simon Lukas , Frisch Tobias , Bente Lisa-Marie , Kacprowski Tim , Thomassen Mads , Reynolds Richard , Baumbach Jan , Röttger Richard , Illes Zsolt TITLE=Hypothesis of a potential BrainBiota and its relation to CNS autoimmune inflammation JOURNAL=Frontiers in Immunology VOLUME=13 YEAR=2022 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.1043579 DOI=10.3389/fimmu.2022.1043579 ISSN=1664-3224 ABSTRACT=

Infectious agents have been long considered to play a role in the pathogenesis of neurological diseases as part of the interaction between genetic susceptibility and the environment. The role of bacteria in CNS autoimmunity has also been highlighted by changes in the diversity of gut microbiota in patients with neurological diseases such as Parkinson’s disease, Alzheimer disease and multiple sclerosis, emphasizing the role of the gut-brain axis. We discuss the hypothesis of a brain microbiota, the BrainBiota: bacteria living in symbiosis with brain cells. Existence of various bacteria in the human brain is suggested by morphological evidence, presence of bacterial proteins, metabolites, transcripts and mucosal-associated invariant T cells. Based on our data, we discuss the hypothesis that these bacteria are an integral part of brain development and immune tolerance as well as directly linked to the gut microbiome. We further suggest that changes of the BrainBiota during brain diseases may be the consequence or cause of the chronic inflammation similarly to the gut microbiota.