Environmental contaminants can trigger itchy skin conditions, including the two most common types of psoriasis: plaque and guttate. In newly published study, researchers discovered the severity of inflammation associated with psoriasis may be suppressed by the aryl hydrocarbon receptor (AhR), a protein in skin cells which senses environmental toxins.

“Because available treatments for psoriasis are not always effective, it might be particularly useful to explore combination therapy with drugs directly targeting the immune system together with different ways of stimulating the AhR pathway,” said Dr. Brigitta Stockinger of MRC National Institute for Medical Research and senior study author.

Psoriasis is a medical condition that affects the immune system and may substantially raise the risk of heart attack in those affected. Plaque psoriasis appears on the skin as raised, red patches covered with a silvery white buildup of dead skin cells or scale. Often itchy and painful, these patches or plaques most often appear on the scalp, knees, elbows and lower back. A less common type of the skin condition, guttate psoriasis appears as small, red, separate spots and often begins in childhood or young adulthood. Together these forms affect 90 percent of the 7.5 million Americans who suffer from this skin condition, which affects slightly more men than women.

Although researchers have identified genetic factors underlying psoriasis, some scientists believe environmental factors, such as the components found in tobacco smoke, might also contribute to the disease. Stockinger suspected that AhR could play an important role in psoriasis, because the receptor is prevalent in skin cells and is known to respond to environmental contaminants such as dioxin, a toxic chemical released into the environment through forest fires, burning of trash, among other sources.

In their recent study of AhR, Stockinger and her research team found that triggering this protein in skin cells with a compound derived from a chemical reaction to UV light exposure reduced inflammation in skin biopsies from psoriasis patients. By comparison, when the team prevented activation of the AhR protein, they found an increase of inflammation. The results of these experiments surprised Stockinger and her colleagues. Psoriasis is a disease with a strong immune reaction, yet the research team found that AhR in skin cells, but not immune cells, were most important to dampening inflammation.

"Currently, the focus for therapeutic intervention in psoriasis is on modulating the activity of immune cells," Stockinger said in a press release. "However, our study suggests that molecules found in skin cells also play an important role in the disease."

Source: Di Meglio P, Duarte JH, Stockinger B, et al. Activation of the aryl hydrocarbon receptor dampens the severity of inflammatory skin conditions. Immunity. 2014.