Science Immunology: One type of tissue-resident memory cell is more resistant to reinfection than another

The immune system's ability to remember disease-causing bacteria that have been defeated and prevent subsequent infections is not entirely clear, but a study in Science Immunology clarifies an important part of
it.

Rutgers researchers used specially bred mice to distinguish the function of two types of immune cells, called tissue-resident memory T cells (Trm cells), that protect against infection and cancer
.
Their work may help improve the efficacy of vaccines and fight a variety of autoimmune diseases
.

"Understanding the role of each Trm cell type allowed us to formulate vaccines that generate the most effective Trm cell types to fight a given infection, and our previous work showed that we can modify the vaccine to alter the balance of the two cell types," said
Tessa Bergsbaken, assistant professor at Rutgers New Jersey Medical College and senior author of the study.
"Trm cells are not always beneficial
.
Certain autoimmune diseases can be driven by Trm cells, and we think what we know will also help us discover how these cells work against us
.
”

Each new infection causes the immune system to design customized T cells (a type of white blood cell) to protect itself
.
After the battle is won, the immune system continues to make the same T cells (in much smaller numbers) in case a particular invader comes back
.

Many T cells circulate throughout the body, "hunting" for antigens they are supposed to guard against, but Trm cells embed themselves in the barrier tissues that isolate the body from the outside world: the skin, eyes, nasal passages, and the entire digestive tract
.
Previous studies have identified different Trm cell subtypes and distinguished them
primarily by the expression of two specific proteins, CD103 and CD69.
However, functional differences between Trm subtypes are unclear
.

In the study, the researchers designed mice to label CD103+ Trm cells, which are produced
in response to a common bacterial infection, Yersinia pseudotuberculosis.
This, in turn, allowed them to distinguish the response of CD103+ cells to reinfection from that of
CD103-Trm cells.

They found that CD103+ cells did not multiply after reinfection and did not directly attack invaders
.
Instead, it is CD103 cells that multiply and attack bacteria
when re-infected.

"What we see is essentially a division of labor between these two different cells, but CD103-Trm cells play a more important role," Bergsbaken said
.
"Producing a higher number of CD103-Trm cells during primary infection or vaccination may be better able to prevent subsequent infections
.
"