NEWS BRIEF - POSTED FRIDAY SEPTEMBER 7, 2007

 

GOOD CELL; BAD CELL

 

If your skin no longer shows the signs of summer—sunburn, poison ivy rash—you may have an unlikely hero to thank. Mast cells, part of the immune system, are notorious for exacerbating problems in the body. But they actually may help skin inflammations heal more quickly, according to new research published in the journal Nature Immunology.

 

Mast cells live in almost all tissues that have blood vessels, but they are not well-regarded. "There's no doubt that until recently they've had a terrible reputation, probably the worst among cells of the blood system," says Stephen Galli, an author on the study and chair of the department of pathology and professor of pathology and of microbiology and immunology at Stanford University School of Medicine in Stanford, California.

 

Mast cells are known to facilitate anaphylactic shock (when blood pressure suddenly drops and the airways to the lungs constrict) in people with peanut allergies. The antibodies that cause anaphylaxis dock on the surface of mast cells. Mast cells are also thought to exacerbate wheezing and coughing in people with asthma. In previous skin inflammation studies, mast cells were shown to make inflammations slightly worse, or at least have no effect, in the first forty-eight hours after the inflammation occurred. LISTEN TO GALLI >> (mp3)

 

With this in mind, Galli and his colleagues looked at the role of mast cells in skin inflammations, including those caused by poison ivy, over a longer time frame. The itchy rash that most of us get when we touch poison ivy (Toxicodendron radicans) or poison oak (Toxicodendron diversilobum) is caused by urushiol oil found on the plant's leaves. Chemicals in the oil form bonds with proteins in the skin.The immune system recognizes the chemicals as foreign, or “non-self,” and then triggers the rash response. LISTEN TO GALLI >> (mp3)

 

But what mediates skin inflammation? In this study, the researchers compared skin inflammation in mice that lack mast cells to mice with mast cells. They found mast cells play a role in the resolution of the rash. LISTEN TO GALLI >> (mp3) The mast-less mice had more swelling, more inflammation and the rash resulted in ulceration. "If you follow their reactions for a long enough period, you see those complex processes that make the reaction go away are greatly enhanced if mast cells are present and occur much more slowly if mast cells are absent. That was the key new finding," Galli explains. LISTEN TO GALLI >> (mp3)

 

How do mast cells help heal skin exactly? The mechanisms are not clear, but the thought is that mast cells produce interleukin 10, a signaling protein that causes cells to reduce their immune response. Galli says: "This could be considered an anti-inflammatory effect or an immunosuppressive effect."

 

The chemicals in the oil of poison ivy happen to be harmless, so preventing the immune response—the itchy rash—is beneficial. But if mast cells produce interleukin 10 to suppress immune response when we have dangerous antigens in our body, the effect is not beneficial. "They have a role like you'd expect in a Clint Eastwood movie," says Galli. "They have a good side and a bad side, an ugly side; they're just complex cells."

 

-Flora Lichtman

 

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