Supplementary files for: How can the MHC mediate social odor via the microbiota community? A deep dive into mechanisms

Genes of the major histocompatibility complex (MHC) have long been linked
to odor signaling and recently researchers’ attention has focused on MHC
structuring of microbial communities and how this may in turn impact odor.
However, understanding of the mechanisms through which the MHC could
affect the microbiota to produce a chemical signal that is both reliable
and strong enough to ensure unambiguous transmission of behaviorally
important information remains poor. This is largely because empirical
studies are rare, predictions are unclear, and the underlying
immunological mechanisms governing MHC-microbiota interactions are often
neglected. Here we review the immunological processes involving MHC class
II (MHC-II) that could affect the commensal community. Focusing on
immunological and medical research, we provide background knowledge for
non-immunologists by describing key players within the vertebrate immune
system relating to MHC-II molecules (which present extracellular-derived
peptides, and thus interact with extracellular commensal microbes). We
then systematically review the literature investigating
MHC-odor-microbiota interactions in animals and identify areas for future
research. These insights will help to design studies that are able to
explore the role of MHC-II and the microbiota in the behavior of wild
populations in their natural environment and consequently propel this
research area forward.