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California Researchers Find Regulatory T Cells Essential to Hair Regrowth

Without Tregs, Hair Follicles Won’t Grow, But Link to Pattern Baldness Uncertain

You’ll probably be hearing a lot more about regulatory T cells in the years to come. Researchers at the University of California San Francisco have determined they play a major role in promoting healthy hair growth. In fact, their article in the journal, Cell, reports that without the contributions of these immune cells, stem cells can’t regenerate hair follicles.

Regulatory T cells are also called Tregs, which sounds like the shorthand name for the Tyrannosaurus Rex — T-Rex. These cells predominantly reside in the lymph nodes, helping to differentiate between harmless and harmful presences in the body. They essentially inform the rest of the immune system of the difference between friend and foe. As described in the article in Cell, “Regulatory T Cells in Skin Facilitate Epithelial Stem Cell Differentiation,” Tregs are increasingly being found in tissues beyond lymph nodes, where they carry out specialized functions that are unique to those tissues.

Tregs regulate immune tolerance, but defects in Tregs give rise to diseases such as autoimmune disorders and allergies. How does this relate to hair loss? It has long been suspected that alopecia areata is an autoimmune disease. The hair follicles shrink and slow hair production, affecting approximately 147 million people worldwide at some point in their lives, including around 6.8 million in the US. Now, Michael Rosenblum, MD, PhD, an assistant professor of dermatology at UCSF and senior author of the article, says defects in Tregs could be responsible.

While more work needs to be done, Dr, Rosenblum says it is possible that Tregs could play a role in other forms of baldness, including male pattern baldness. For one thing, it’s unclear whether men and women with androgenetic alopecia have defective Tregs. But what is clear is that for hair follicles to regenerate, Tregs must be present.

“Our hair follicles are constantly recycling: when a hair falls out, a portion of the hair follicle has to grow back,” said Dr. Rosenblum. “This has been thought to be an entirely stem cell-dependent process, but it turns out Tregs are essential. If you knock out this one immune cell type, hair just doesn’t grow.”

As was the case in several other recent discoveries, this one was accidental. Hoping to better understand the role Tregs that reside outside the lymph nodes, Rosenblum developed a technique for temporarily removing Tregs from the skin of mice. However, when they shaved patches of hair from these mice, they noticed that the shaved patches of hair did not grow back.

When they examined the role of Tregs further, they found substantial evidence that Tregs evolved in tandem with the stem cells, “so that the Tregs not only guard the stem cells against inflammation but also take part in their regenerative work.” Among their findings:

  • In imaging experiments, the research team observed a three-fold increase in the number of active Tregs around the stem cells during the growth phase of the hair follicle regeneration cycle.
  • Researchers found that once follicle regeneration has started, removing Tregs has no impact on hair regrowth, but removing them during the first three days after shaving skin halts regrowth entirely.
  • The team determined that Tregs send hair regeneration signals through a pathway that communicates directly with the hair follicle stem cells.

“We think of immune cells as coming into a tissue to fight infection, while stem cells are there to regenerate the tissue after it’s damaged,” said Dr. Rosenblum. “What we found here is that stem cells and immune cells have to work together to make regeneration possible.”

We at Arocha Hair Restoration believe the discovery that Tregs play a key role in stem cell activation is an exciting addition to our understanding of hair loss. We tip our hat to Dr. Rosenblum, lead author Niwa Ali, PhD, and their research team at UCSF. We further want to recognize the support of the US National Institutes of Health, the Burroughs Wellcome Fund, Scleroderma Research Foundation, the National Psoriasis Foundation and the Dermatology Foundation which provided financial support for the research.

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