The Immunometabolic Interface Between Host and Microbiota

Immunometabolism is the study of immunity and metabolism as an integrated system. The prototypical organ for such study is the gut. Central to the proper and optimum functioning of the gut, thus its immunometabolism, is the microbiota. Often the microbiota is considered only in the context of what functions, molecules and signals it provides to the host. However, the interactions between the host and microbiota must fundamentally be understood as bidirectional communication. In the realm of metabolism, it is clear that the microbiota provides critical metabolites to the host, for example through bacterial fermentation of indigestible feed components. The host also provides a nutrient source for the bacteria of the gut, an example being glycans in mucus feeding mucosal-associated commensal bacteria. In the realm of immunity, significant research has been conducted on how microbiota signals aid in proper immune development. An early microbial colonization from the mother can aid her offspring immunologically throughout life. The immune system also dictates which microbes may reside on mucosal surfaces. Only in understanding all of these communication pathways, can we start to uncover the complex host-microbiota interface, and start to critically evaluate intervention strategies in context. Tradeoffs must also be understood in animal production, for example, a diverse microbiota can benefit host immunity and disease resistance, but may reduce optimal feed fermentation. When considering nutrition, feed additives and antibiotic alternatives we must study both the indirect and, critically, direct impacts of both metabolism and immunity on both host and microbiota simultaneously.