OR precedes the development of OA, but its incidence is largely underestimated compared with that of OA. Previous studies have shown that high-molecular-weight agents such as laboratory animal allergens, flour, plant allergens, and biological enzymes can cause OR, with a prevalence of 2 to 87%.4,9
Rhinoconjunctivitis symptoms have been confirmed as one of the most significant factors in the development of OA.10
Continued exposure of the patient in the present study to rice powder may lead to the development of asthma, as suggested by previous studies.
The monitoring of airborne rice pollen in agricultural fields has revealed a high intensity of the released allergen.11
A cross-sectional study in rice farmers reported the prevalence of upper and lower respiratory symptoms such as hay fever (25.7%), watery eyes (14.9%), chronic cough (7.1%), and physician-diagnosed asthma (7.1%),12
indicating that occupational exposure to rice may trigger a respiratory allergy in workers and people living in the vicinity. However, immunological evaluations were not performed to confirm the causal relationships. In the present study, the patient showed positive responses to a skin prick test and high serum specific IgE to rice extract, as well as work-related symptoms.
Several allergenic components in rice have been described, including Ory s 1 (35 kDa), a 14- to 16-kDa member of the α-amylase/trypsin inhibitor family, a 33-kDa allergen with glyoxalase I activity, and a 9-kDa lipid transfer protein (LTP).5,13
Ory s 1 protein shows cross-reactivity with rye and Bermuda grass pollens in patients with a pollen allergy and shares significant sequence identity with the major pollen allergen of rye grass (Lol p 1; 65.5% identity) and Bermuda grass (Cyn d 1; 62.9% identity). 14
Moreover, LTP is known as a pan-allergen with cross-reactivity to botanically unrelated plants.15
Cross-reactivity between peach and rice LTP has been confirmed in several rice allergies, including anaphylaxis after rice ingestion16
and rhinitis with asthma caused by rice inhalation.15
In the present study, dose-dependent inhibition was observed when rice extracts and grass pollens were added in an IgE ELISA inhibition test, suggesting cross-reactivity. Therefore, immunotherapy with grass pollen allergens may be effective in this patient.
A nasal provocation test with rice extracts showed increased ECP as well as increased symptom scores for 3 hours after provocation. These results are consistent with previous studies demonstrating that a single allergen challenge test can induce a late response characterized by local accumulation of eosinophils and release of various mediators.17
In particular, the ECP level increases 1 or 2 hours after the challenge, reflecting the influx and activation of eosinophils in the late allergic phase. In previous studies, an increased ECP level was paralleled by an increased level of the typical TH2 cytokine interleukin-5,18
and elevated ECP was maintained for 24 hours after provocation, with a significant correlation to nasal symptom intensity,19
similar to the results of the present study.
In conclusion, we confirmed that rice powder inhalation can induce OR, in which an IgE-mediated mechanism was suggested.