Contact sensitization to calocephalin, a sesquiterpene lactone of the guaianolide type from cushion bush (Leucophyta brownii, Compositae).

BACKGROUND

Cushion bush [Leucophyta brownii Cass. = Calocephalus brownii (Cass.) F. Muell.] is an Australian Compositae shrub that has been introduced into Scandinavia as a pot plant. The first case of sensitization occurred in a gardener, and the main allergen was identified as the guaianolide calocephalin.

OBJECTIVE

To present the identification of the main allergen, and to assess the prevalence of sensitization to calocephalin in Compositae-allergic patients.

METHODS

Calocephalin was isolated from a dichloromethane extract of aerial parts of cushion bush. Calocephalin 0.1% ethanol was included in the plant series in Malmö, Sweden, and Odense, Denmark.

RESULTS

Nuclear magnetic resonance (NMR) analysis of calocephalin resulted in a revision of its chemical structure to 4α-acetoxy-1α,2α-epoxy-5α,10αH-guai-11(13)-en-12,8β-olide. The prevalence of patch test positivity was up to 28% in aimed patch testing. Despite strongly positive patch test reactions, the relevance was unknown in the majority of cases, and only 1 person was occupationally sensitized.

CONCLUSIONS

Calocephalin is a potent contact allergen, but, as cushion bush is a low-maintenance pot plant, primary sensitization is most likely to occur through occupational exposure. Positive reactions in Compositae-sensitive persons probably occur because of cross-reactivity, and patients should be warned about contact with cushion bush plants.