Trial for developing a reference extract for future standardization of Japanese cypress pollen extracts

Japanese cedar pollinosis (JCP) is the most prevalent seasonal allergic rhinitis in Japan. Many JCP patients are also sensitized to Japanese cypress pollen (JCyP), and their symptoms become exacerbated and prolonged during the JCyP dispersal period after JCP. To date, there have been no reports on the development of JCyP-specific allergen immunotherapy. For the future development of a JCyP-specific skin test and immunotherapy, we sought to develop a reference extract for future standardization of JCyP extract determined by the average threshold dilution eliciting a positive response in the intradermal skin test.

A 1:20 antigen extract (Lot AA) was prepared from JCyP grains by the glycerin extraction method. The protein and allergen concentrations in the extract were determined. After confirming its safety, 3-fold serially diluted solutions of JCyP extract were prepared from Lot AA. The average threshold dilution eliciting a positive response in the intradermal skin test was determined among Japanese subjects with serum JCyP-specific IgE class of 2 or higher according to ImmunoCAP IgE assays or View39 IgE assays.

The protein concentration in Lot AA was 4.7 mg/mL, and the allergen concentration was 18.8 μg/mL for Cha o 1 and 1.1 μg/mL for Cha o 3. In total, 85 individuals were registered for this study and finally, 55 subjects were left for the analysis. The threshold dilution for an intradermal reaction was 3⁶ in 32 individuals (58.2 %), 3⁷ in 8 individuals (14.6 %), 3⁸ in 4 individuals (7.3 %), and 3⁹ in 1 individual (1.8 %); no reaction was seen in 10 individuals (18.2 %). The average threshold dilution was 3^6.4, which is equivalent to a 1131-fold dilution. No serious adverse events were observed at any of the tested dilutions.

The results showed that Lot AA of JCyP extract exhibited in vivo allergic potency and was safe. Thus, it may be useful as a future standardized antigen of JCyP or a reference antigen for standardizing other JCyP extracts for the diagnosis and treatment of JCyP pollinosis.