Gut segments have different immune system functions

(Credit: Pete Ashton/Flickr)

Researchers have discovered that the intestine consists of different compartments that pace the immune system’s reactions to food passing through.

The food-processing canal has less aggressive defenses in the first segments where it absorbs nutrients, and more forceful responses at the end, where the body eliminates pathogens, according to the research in mice.

The findings, which appear in Nature, provide new insights about how the intestine maximizes nutrient uptake while protecting the body from potentially dangerous invading microbes, two seemingly conflicting functions.

The research has potential to improve drugs for gastrointestinal disorders, as well as inform the development of oral vaccines.

The gut’s immune system functions differently in distinct parts of the intestine, the new research shows. (Credit: Rockefeller)

“At first glance the intestine appears uniform throughout,” says Daniel Mucida of Rockefeller University. “But we’ve found a sophisticated functional system lurking beneath the surface, organized in segments to allow different immune system functions in different locations.”

Mucida and colleagues uncovered a functional segmentation in mice by examining intestinal structures called gut draining lymph nodes, which orchestrate immune responses. The researchers found that nodes in different part of the intestine had different cell composition, and when they challenged the mice with a pathogen such as Salmonella, they saw different immune responses between segments.

Having immune responses separated by location likely increases the chance that the immune system reacts appropriately to what’s passing through, Mucida says. Once the body has absorbed most nutrients, the system can focus more aggressively on eliminating pathogens without interfering with food uptake.

Scientists could exploit the immunological differences between the gut segments for a number of therapeutic purposes, including for treating gastrointestinal disorders, according to Mucida.

For example, by targeting immune-suppressing drugs to the segment where they’ll have the most effect, it might be possible to dampen their side effects. Additionally, outcomes of surgeries that remove part of the intestine could improve by taking into account variations between segments.

The spectrum of immune responses along the intestine could help make new and better oral vaccines. Thus far, the difficulty of generating a robust immune response has stymied scientists’ efforts to design oral vaccines—attractive to many because of the absence of needles (and unless the immune system mounts a strong enough reaction to the vaccine, it cannot create the molecular “memory” of the pathogen needed to prepare the body against recurring attacks).

According to Mucida, the muted immune response at the beginning of the intestine might be part of the reason why oral vaccines tend to be less effective than injections.

“In theory, targeting the distant end of the intestine could be more efficient in inducing the immune response required,” he says.

“If we harness the right region of the gut, we might see some vaccines work that have previously failed.”

Source: Rockefeller University