When pathogens enter the human body, a large number of immune cells quickly become available to recognize and destroy invaders. These cells include T cells, a type of white blood cell that can directly recognize pathogens, such as viruses or bacteria. T cells are often referred to as “blood cells,” a misleading term, while research shows that T cells sometimes stay in the skin for years.
In fact, the majority of T cells remain in the tissues,
The main author, Christina Zielinski, points out: “T lymphocytes have long been thought to circulate only briefly in tissues, for example to fight infection, but do not linger on them, then migrate directly into the bloodstream.”. Our research shows that in fact most of the T cells remain in the tissues in the long run, and that they are much less likely to actually circulate in the body.
Thus, blood samples could be very little indicative of the quality of a subject’s immune defenses.
Track “T” cells: this is what this team has achieved from samples from patients who have received allogeneic stem cell transplants. The immune systems of these participants had been destroyed by chemotherapy and radiation therapy and then rebuilt using a donor’s blood stem cells. The researchers looked at skin biopsies and blood samples taken 2 to 3 years after stem cell therapy. This allowed them to determine if the T cells they found were from the patient or the donor and were able to determine the genetic footprint of the patient’s cells. These analyzes show that:
- half of the T cells in the skin came from the patients themselves, while in the blood, the T cells came almost exclusively from donors;
- in other words, the patient’s own immune cells survived for years in the skin tissue;
- however, only about a quarter of the recipients of stem cell therapy had this profile; the immune system had been completely renewed in the other participants;
- however, this is sufficient to demonstrate that T cells can reside in the skin tissue for years.
What are the implications? These resident T cells could have a protective function, could prevent the donor cells from entering the tissue and thus prevent an inflammatory reaction. The resident T cells found here in the skin tissues did have anti-inflammatory properties.
The question deserves to be asked in the case of an organ transplant, such as a liver transplant: Again, the question is whether the remaining T cells in the tissue – in this case the donor – can possibly protect the organ from rejection.
Resident cells have very specific characteristics: this work also reveals that resident T cells are optimally adapted to the skin and can thus specifically support its function as a barrier against pathogens. By using new single-cell RNA sequencing techniques, it becomes possible to identify the movements of memory T cells that leave the tissues and can then be found in the bloodstream. The identification of genetic markers of resident T cells may allow further study of their function and, if necessary, their use in cell, skin or other organ transplants. .