The skin of an adult human being measures about 1.5 square metres and weighs approximately four kilos for an average-sized individual. It’s not only the largest organ in our body but is also our first major protective barrier, defending the body from bacteria, harmful chemicals and extreme temperatures. But what do its physical well-being and resilience depend on? A new study from Spain’s National Centre for Cardiovascular Research (CNIC) has revealed that the immune system may play a key role.

In this latest edition of News from the Lab, CaixaResearch researcher Andrés Hidalgo and “la Caixa” Foundation fellow Tommaso Vicanolo explain their new finding, published in the journal Nature. They have discovered that a special type of immune cell (called neutrophils) is capable of modifying the resistance and permeability of the skin, revealing that the immune system not only fights infections but also physically reinforces our great barrier to repel external attacks.

Neutrophils are immune cells in the blood known for defending against infection, but Hidalgo and Vicanolo’s work has revealed an unexpected role: neutrophils are able to penetrate the skin to generate collagen and other proteins that help strengthen the skin barrier. These cells reinforce the skin under normal conditions but also react actively to injury, forming protective structures around wounds to stop bacteria or toxins from entering.

“Moreover, we observed that these neutrophil functions are influenced by circadian rhythms, i.e. they act differently depending on whether it’s day or night” explains Tommaso. “In fact, neutrophils enter the skin at night, making this tissue harder and less flexible. This invites us to investigate further how the body’s internal rhythms influence tissue regeneration and repair”.

The study also revealed that this structural function of neutrophils is regulated by a set of signals we call the TGF-β pathway. When this mechanism was deactivated, the researchers observed that the skin became more fragile and permeable. “This suggests that the interaction between the immune system and the structure of our skin is more complex than previously thought” notes Andrés, who is currently at the Yale School of Medicine in the United States.

Although this finding has been made in animal models, the researchers say they have found evidence that the same is true in people, where neutrophils are very abundant. 

This discovery opens up new avenues for understanding the immune system and could also inspire treatments for skin diseases and immune system disorders. “These findings are likely to have implications for therapies aimed at strengthening the skin barrier in people with inflammatory diseases, diabetes and ageing, among many other conditions” Andrés concludes.