Allergic contact dermatitis caused by Lithraea molleoides and Lithraea brasiliensis: identification and characterization of the responsible allergens

Abstract

Background: Allergic contact dermatitis caused by species of Lithraea genus (Anacardiaceae) is frequent in South America. Nevertheless, it has been scarcely reported in the literature, hitherto the responsible allergens have not been studied in some species.

Objective: The purpose of this study was to identify and characterize the allergenic compounds of Lithraea molleoides and brasiliensis, and to investigate the existence of cross-reactions with Toxicodendron allergens.

Methods: Twenty-seven South American subjects (17 with previous Lithraea dermatitis and 10 controls without any plant dermatitis) and four North American subjects who are highly sensitive to poison oak were tested with both purified Lithraea molleoides and brasiliensis extracts and poison oak urushiol. Lithraea extracts were analyzed by gas liquid chromatography (GLC) and gas chromatography-mass spectrometry (GC-MS).

Results: All 17 Lithraea-sensitive subjects reacted to poison oak urushiol and 13 of them also reacted to Lithraea molleoides and/or brasiliensis extracts. All 4 poison oak sensitive subjects reacted to poison oak urushiol and to Lithraea extracts. In both groups of sensitive subjects, the responses to poison oak urushiol were stronger and occurred at lower concentration than those to Lithraea extracts. The allergenic fraction in both Lithraea species consisted of: 3-pentadecylcatechol, 3-pentadecenylcatechol, 3-heptadecenylcatechol and 3-hepta-dec-dienilcatechol.

Conclusion: We concluded that Lithraea molleoides and brasiliensis allergens are closely related to urushiol, although their eliciting potential seems to be lower in comparison with poison oak urushiol, even for Lithraea-sensitive subjects.