The gut microbial metagenome encodes a diverse array of functions that complement host genes involved in metabolism. In support of this idea, the gut microbiomes of obese individuals are characterized by reduced species richness and metabolic capacity. Thus, maintenance of the diversity and collective functional capacity of the microbiota is likely vital to the promotion of optimal metabolic health throughout life. One mechanism to maintain a diverse microbiota is through T cell–dependent immunoglobulin A (IgA) production. However, the relationship between IgA and the development of obesity remains unknown. Although studies of obesity and metabolic syndrome have highlighted a direct role for inflammation, overweight individuals also evince some diminished immune responses, such as reduced levels of mucosal IgA. Thus, microbiota maintenance through IgA may affect functions within both the microbiome and, subsequently, the host metabolism.
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