Podocarpus gracilior and Callitris verrucosa--newly identified allergens that crossreact with Cupressus sempervirens

Thirty-six symptomatic patients, with positive skin reactions to Cupressus sempervirens pollen extract were skin-tested with pollen extracts of Podocarpus gracilior and Callitris verrucosa, of these 17 (47%) had positive responses to P. gracilior, nine (25%) to C. verrucosa, and six (17%) to both. None of the non-atopic healthy controls had positive reactions to either of the extracts. Radioallergosorbent test (RAST)-inhibition studies were performed with pooled sera from three patients. Fifty per cent inhibition was obtained with 11 micrograms protein of C. sempervirens, 54 micrograms of P. gracilior, and 71 micrograms of C. verrucosa; however, when pollen extract of Olea europaea, an unrelated allergen, was tested, 265 micrograms protein were needed to obtain 50% inhibition. One-dimension sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of pollen extracts from the three species revealed that they had several very similar protein bands. Using Western blot analysis, several closely related IgE binding proteins were identified in the three species. It was concluded that the pollen grains of P. gracilior and of C. verrucosa are potentially allergenic. The presence of common allergenic proteins indicate partial crossreactivity with C. sempervirens.