Clinical Relevance

IgE-mediated reactions

Although only sparse reports document sensitisation to Red cedar, anecdotal evidence suggests that asthma and hayfever are possible following exposure to pollen from this tree. Red cedar has been reported to be a significant cause of early spring hayfever, and occasionally asthma, in the southeastern states of the USA. “Cedar” pollens may also be significant allergens in areas where they are prevalent but their effects have not been suspected. Red cedar and White cedar (Thuja occidentalis) are common plants in western New York State. In an examination of skin test results from 158 patients with asthma, rhinitis, or both, 102 had positive skin tests to at least 1 pollen. Among those, 52 patients (51%) had positive skin tests to at least 1 of the Cedar pollens. Patients sensitive on skin testing to Cedar pollen were very likely to be sensitive to deciduous tree, grass, or Ragweed pollen. The authors stated that sensitivity on skin testing to indigenous Cedar pollens was common in this region and therefore could be clinically significant

Other reactions

uniper tar (cade oil) is distilled from the wood of the Prickly juniper tree (J. oxycedrus) and contains etheric oils, triterpene and phenols. It is used for many purposes in folk medicine. An individual who ingested a spoonful of homemade Juniper tar developed fever, severe hypotension, renal failure, hepatotoxicity, and severe cutaneous burns on the face. Whether a similar result would occur from Red cedar is unknown.

Cross-Reactivity

The group 1 allergens of other “Cedar” trees are reported to be a major cause of pollen hypersensitivity in several geographic areas, and allergens from several taxa have been shown to cross-react. Although cross-reactivity of Red cedar has not been elucidated, an inference of cross-reactivity with other pollens may be made from knowledge of its closely related genus member, Mountain cedar. For example, cross-reactivity has been reported between the group 1 allergen from Mountain cedar (Jun a 1) and Japanese cedar (Cry j 1). High cross-reactivity (75-90% homology) has been reported between Cup a 1 (C. arizonica), Cha o 1 of Japanese cypress (Chamaecyparis obtuse) and Jun a 1, the major allergen of Mountain cedar; all have an active pectase lyase site. The authors concluded that the high degree of homology of Jun a 1 with Cha o 1 and Cry j 1 may explain the cross-reactivity of conifer pollens.

Similarly, Cup a 3 from C. arizonica, a thaumatin-like, pathogenesis-related protein, was shown to have a high homology with Jun a 3 from Mountain cedar.