Researchers Discover the Molecule Responsible for Poison Ivy Reactions

Scientists have discovered which immune molecule is responsible for the body’s reaction to poison ivy. The findings can be used to develop treatments for poison ivy rashes and inflammatory skin diseases. The details are in a paper just published in the journal Nature Immunology.

Poison ivy (Toxicodendron radicans) is a poisonous plant found throughout Asia and North America. The plant is actually not a true ivy but is instead related to cashew trees. When the plant is touched, it causes an itchy rash on the skin that can persist for weeks. The source of the rash is an allergic reaction to a compound called urushiol. Not everyone is allergic but for most people, simply brushing against a poison ivy plant is enough to cause the reaction.

Researchers from Harvard and Monash University studied a lipid-presenting molecule used in the body’s immune system responses. The molecule, called CD1a, is found in human skin. Although the molecule is very common in the human body, there have been few studies investigating its functions. This is because CD1a isn’t found in standard laboratory animals such as mice.

The research team modified mice so that they expressed the CD1a molecule. The researchers found that mice that expressed CD1a developed rashes when exposed to urushiol compounds. CD1a reacts with urushiol and triggers a chain of events that result in sudden inflammatory responses. The reaction resulted in a specific cytokine signature. The same cytokines were found in urushiol-sensitive human subjects who had been recently exposed to poison ivy.

When the team blocked CD1a activity in mice, the reactions to urushiol stopped and skin inflammation was alleviated. The authors hope to further investigate the properties of CD1a to determine the best possible treatments. CD1a-blocking molecules are a good place to start since they alleviated symptoms in mice. The team also believes that their findings could help develop treatments for other skin diseases, including psoriasis, rosacea, and eczema.


Ji Hyung Kim et al. CD1a on Langerhans cells controls inflammatory skin disease. Nature Immunology (2016).

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