Scientists Discover New 'Micro-organ' Hiding in Our Immune System

Scientists have discovered a new "micro-organ" within the immune system, according to a study published in the journal Nature Communications.

Researchers from Australia's Garvan Institute of Medical Research identified a structure that "remembers" past infections and vaccinations—and is filled with immune cells of many kinds which respond to pathogens that the body has encountered before.

The structure is strategically positioned on the outside of lymph glands to detect infections early, according to researchers. It was discovered when the team used an advanced imaging technique, known as "3D microscopy", to essentially create "movies" of the immune system in action inside living animals.

"The [micro-organ] was identified by a sophisticated microscopy technique called intravital two-photon microscopy," Tri Phan, who led the research, told Newsweek. "This allows us to perform three-dimensional imaging in real-time by taking hundreds of 'slices' of the lymph node in a live animal in the same way a CAT scan takes hundreds of slices of a patient."

"By reconstructing the slices into a three-dimensional volume and watching the cells move and interact with each other, we were able to clearly see this new structure," he said.

Humans have long known that people who are exposed to an infection are often left with some immunity afterwards. However, certain questions still remain regarding exactly how this process works.

The structure is thin, flat and only appears when animals are exposed to an infection that the body has seen before. Named SPF—or "subcapsular proliferative foci"—researchers detected it in both mice and humans.

When the team used microscopy techniques to view the SPF in the body, they saw several different types of immune cells inside it, including "memory B Cells" which carry information about how best to attack infections. Crucially, the scientists observed that the memory B cells were changing into plasma cells.

"[The] specific purpose of SPF is to rapidly generate large numbers of plasma cells to make the antibodies needed to protect us from reinfection," Phan said. The location of the SPF structures is also perfectly suited to fighting infection.

"The SPF is located strategically where bacteria would re-enter the body and it has all the ingredients assembled in one place to make antibodies—so it's remarkably well engineered to fight reinfection fast," Phan said in a statement.

The researchers say that the SPF has never been identified before because they it is hard to see with traditional microscopy techniques—which only look at 2D slices of tissue—due to the fact it is thin and only appears at certain times.

Immune cells (pink and green) gathering at the subcapsular proliferative locus (SPF), a newly discovered immune system structure that appears in the lymph node. Blue = surface of the lymph node Imogen Moran & Tri Phan/Garvan Institute

"So, this is a structure that's been there all along, but no one's actually seen it yet, because they haven't had the right tools," Phan said in the statement. "It's a remarkable reminder that there are still mysteries hidden within the body—even though we scientists have been looking at the body's tissues through the microscope for over 300 years."

The latest results could help scientists to better understand how to develop more effective vaccines, according to the researchers.

"In the past we have focussed on developing vaccines that produce plasma cells and memory B cells, but not on how and where these memory B cells get reactivated," Phan told Newsweek. "This study suggests that the best place for memory B cells to get reactivated is the SPF, which is engineered to produce a very fast and very strong antibody response to eliminate infectious pathogens."

"So one possible new direction for vaccine design would be to try and generate memory B cells that would position themselves in the SPF, rather than mislocalize outside the lymph node in other tissues and organs."

This article has been updated to include additional comments from Tri Phan.