Study shows how immune cells organize themselves in the epidermis

The human skin is essentially an organ, a fact that that is easy to forget. It is also the largest organ and is continuously exposed, charged with keeping the human inner biology safe from the threats of the outside world.

However, Sangbum Park from Michigan State University (MSU) is someone who never takes skin or its biological activities for granted. He is investigating skin at the cellular level to better interpret it and help scientists support it when it is combating disease, infection, or injury.

In the new installment of that effort, Park, who works in IQ—the Institute for Quantitative Health Science & Engineering at MSU—has helped demonstrate how the immune cells of the skin assemble themselves to prevent would-be intruders. Park and his collaborators have published their results in the Nature Cell Biology journal.

Immune cells are the soldiers of our body. In our skin, that army is maintained according to two factors: density and distribution.”

Sangbum Park, Assistant Professor, Department of Medicine and Department of Pharmacology and Toxicology, College of Human Medicine, Michigan State University

“We need enough immune cells to cover the whole area of our skin uniformly for proper protection. Otherwise, our skin would be vulnerable to damage and infection. As sensible as that might sound, it was unclear how, or even if, these immune cells were organized before this study. Many researchers thought the cells' distribution was random,” added Park.

The immune cells of the skin have a history of being misinterpreted. A majority of people do not know that the outermost layer of skin, called the epidermis, is home to immune cells. When Paul Langerhans, the German scientist, initially discovered a specific type of these immune cells in the late 1800s—cells that are presently known as Langerhans cells—he mistook them for cells from the human nervous system (to be reasonable, they share a similar morphology).

Hence, to shed more light on how the immune cells of the skin perform their jobs, Park and his colleagues used advanced microscopy tools. The investigators revealed how live immune cells organized themselves in the skin of mice—a well-known animal model whose skin biology analogous to that of human beings.

“IQ has so many advantages for a young investigator like me,” added Park, who became a part of MSU in January 2020. Just a couple of months later, Park had to start working from home because of the ongoing coronavirus pandemic. But due to IQ’s robust microscopy core, Park’s research group was able to work almost instantly as restrictions were lifted.

I didn’t have to wait to set up microscopes in my own lab or train my students how to use them. At IQ, we already have many different microscopes for a wide range of animal models.”

Sangbum Park, Assistant Professor, Department of Medicine and Department of Pharmacology and Toxicology, College of Human Medicine, Michigan State University

Consequently, Park’s research group was able to demonstrate the function and structure of the skin like never before. After verifying these latest methods and visualizing how immune cells are arranged in the mice’s healthy skin, Park’s research team can start asking new questions about the way the skin heals.

“My lab is interested in how skin regenerates and recovers from injury,” Park added. That kind of injury could be an infection, an allergic reaction, a cut, or even more persistent disorder, like psoriasis.

We can answer so many questions with our intravital imaging technique that you just can't with conventional methods.”

Sangbum Park, Assistant Professor, Department of Medicine and Department of Pharmacology and Toxicology, College of Human Medicine, Michigan State University