Another path to better understand hair loss. Scientists at the Salk Institute in California accidentally discovered that regulatory T cells have the ability to regrow hair in cases of hair loss caused by alopecia areata (alopecia areata). This specific type of alopecia is caused by an abnormality in the immune system and is characterized by hair loss in the form of spots, of different sizes, in several places on the scalp (when alopecia areata affects the whole head, we are talking about alopecia areata total). According to the Sentinel study dated 2004, there are approximately 78,000 cases of alopecia areata in France, affecting patients between the ages of 2 and 94. The Nature Immunology publication explains how regulatory T lymphocytes, known for their role in the immune system, are also able to regulate hair growth using a hormone as a messenger to hair follicles.
Immune reaction against hair follicles
For a long time, regulatory T cells have been studied in the context of excessive immune reactions. It’s actually a bit special: while immune cells generally fight off external attacks, regulatory T lymphocytes are responsible for suppressing an immune reaction that can be very powerful. A way to reduce inflammation. When this function is disturbed, a disease can occur: allergies, for example, are reactions of the immune system to a substance, which are completely disproportionate. Inflammation also has a role in alopecia areata. In severe alopecia areata, immune cells attack skin tissue. Current treatments, based on glucocorticoids, consist in suppressing the skin’s immune reaction so that it does not continue to attack the hair follicles.
The Salk Institute discovery was also serendipitous, as researchers were studying the role of regulatory lymphocytes in certain autoimmune diseases, such as multiple sclerosis, Crohn’s disease, or even asthma. They then realized that regulatory T lymphocytes and glucocorticoids do not interact together in the context of these diseases. The scientists then decided to monitor environments in which regulatory T cells express very high levels of glucocorticoid receptors, such as in skin tissue. Working on shaved mice, the team observed that there was no hair growing back in animals that lacked glucocorticoid receptors in regulatory T cells. On the other hand, in normal mice that lost their hair, the latter were able to grow again. “We have identified upstream hormone and downstream growth factor signaling that actually promote hair growth and regeneration quite separately from suppressing the immune response.‘, explains to Science and the future Professor Yi Zheng, of the Salk Institute’s Center for Immunobiology and Microbial Diseases.
Stop hair loss and regrow hair
The findings of scientists at the Salk Institute shed new light on current treatments for alopecia areata. So there will be an interaction between T lymphocytes and hair follicle stem cells, which leads to hair regeneration. Specifically, glucocorticoids direct T cells to activate hair follicle stem cells. “Our findings suggest that current glucocorticoid-based hair loss treatments not only suppress inflammation in patients with alopecia areata. [pour freiner la chute, ndlr]. It also helps to rejuvenate the hair through its effect on the hair follicles.Ye Cheng explains.
For the interaction to work, glucocorticoid receptors stimulate production of the TGF-beta3 protein inside T lymphocytes, and this activates the stem cell and causes it to transform into new hair follicles, allowing new hair to grow. This mechanism, quite distinct from other immune functions, is not dependent on the action of T lymphocytes on the immune system. Normally, T cells do not produce TGF-beta3. This mechanism is triggered only in damaged muscle or heart tissue. Going forward, the team now wants to study the regenerative function of regulatory T cells in more detail. Their new project involves isolating them from affected tissue to monitor levels of TGF-beta3, as well as other growth factors.