Does the immune system control hair growth?

The Immune System and Hair Growth

Every now and then, I share a landmark study which has the potential to change the way we think about the hair follicle, and how it grows. Today is one of those days.

Researchers at the University of California San Francisco reported last week an important new finding: without specific immune system cells called T regulatory cells (T regs), hair follicles do not grow properly. The study was performed in mice, but likely has relevance to humans.

T regulatory cells are important immune cells. Mice have them and so do humans. These immune system cells act as sort of peacekeepers of our immune system. In scientific terms, we say that these cells play a key role in ‘immune tolerance.’ They tell other immune cells of our body to stay quiet when the time is right to stay quiet and this helps prevent unnecessary allergies and autoimmune diseases. To study the role of T regulatory cells, the researchers developed a clever mouse model whereby T regulatory cells could be removed from the mouse whenever desired. In these studies, mice were shaved of hair and hair regrowth patterns were observed. Surprisingly, hair did not regrow after shaving.

There has now been a shift in thinking. Hair follicle stem cells, at least in mice, appear to listen to the commands of T regulatory cells to know when to grow – and when to stay quiet. Tregs are now understood to accumulate around hairs at the end of the hair growth cycle (in the telogen phase) and help direct hair follicle stem cells to make a new hair. Without Tregs, the growth phase (anagen phase) does not begin. This information could have direct relevance to humans and our understanding of a variety of hair loss conditions. It is well known from previous studies for example, that many of these genes that contribute to the condition alopecia areata are in fact genes that regulate T regulatory cells. In addition, other studies have shown that by supporting T regulatory cells in their functioning, it is possible to can help regrowhair in alopecia areata.

Reference
Ali et al. Regulatory T Cells in Skin Facilitate Epithelial Stem Cell Differentiation. Cell 2017.