Topic Overview:

Humans exist as a combination of host cells and a vast consortium of bacteria, viruses, and fungi called the microbiota that overwhelm the host both in terms of cell number and genetic information. Adaptive immunity has evolved alongside the microbiota, suggesting the cardinal feature of adaptive immunity, known as immunological memory, may be an effort to “remember” previous responses and shape subsequent host-microbial interactions to maintain homeostasis.

Gastrointestinal infection constitutes a particularly dangerous setting because it has the potential to permanently change the relationship between the microbiota and host, blurring the lines that define pathogens versus symbionts. Hand and colleagues have now identified multiple ways in which infection alters the immune response to the microbiota, including shifts in the microbiota toward dysbiosis, the development of long-lived, microbiota-specific T cells, and disruption of microbiota-immune interaction due to lymphatic scarring. Hand expects this work will help researchers understand the root causes of diseases that are characterized by a disrupted relationship between the immune system and the microbiota, such as Crohn’s disease and environmental enteropathy.