A clinical case of anaphylaxis after eating oatmeal contaminated with booklice (Liposcelis bostrychophila).

A 52-year-old man presented to our department with generalized erythema, watery stools, and vomiting 30 min after ingesting coconut, oatmeal, and vegetable juice. On arrival, his blood pressure was 120/79 mm Hg, heart rate was 126 beats per min, blood oxygen saturation was 96%, and lip cyanosis was observed. The patient experienced diffuse redness throughout the body and was diagnosed as having severe anaphylaxis. A skin prick test for the leftover coconut, oatmeal, and vegetable juice, which the patient had consumed immediately before the onset of symptoms, showed a positive reaction only to the leftover oatmeal. Direct microscopic examination of the leftover oatmeal revealed numerous insect bodies that appeared as booklice. Using Western blot analysis and quantitative polymerase chain reaction, Lip b 1, a specific antigen for Liposcelis bostrychophila (badonnel), an indoor pest that inhabits various places and feeds on various indoor materials, including stored foods, was detected only in the extract of the leftover oatmeal. Based on these results, we identified an insect body infesting oatmeal, L. bostrychophila. The serum level of L. bostrychophila-specific immunoglobulin antibodies was higher than the cutoff value; therefore, we identified the disease as anaphylaxis caused by accidental ingestion of L. bostrychophila that infested the oatmeal stored in the container. We report the first case of L. bostrychophila-infested oatmeal as an orally ingested allergen in Japan.

Crystal structure of the dog allergen Can f 6 and structure-based implications of its cross-reactivity with the cat allergen Fel d 4.

Several dog allergens cause allergic reactions in humans worldwide. Seven distinct dog allergens, designated Canis familiaris allergen 1 to 7 (Can f 1-Can f 7), have been identified thus far. Can f 6 shows high sequence similarity and cross-reactivity with Fel d 4 and Equ c 1, major cat and horse allergens, respectively. This study was conducted on the allergenic epitopes of Can f 6 based on its structural characterization. We demonstrated that sera from 18 out of 38 (47%) dog-sensitized patients reacted to recombinant Can f 6 protein (rCan f 6). We then determined the crystal structure of rCan f 6 by X-ray crystallography, which exhibited a conserved tertiary structural architecture found in lipocalin family proteins. Based on the tertiary structure and sequence similarities with Fel d 4 and Equ c 1, we predicted three IgE-recognizing sites that are possibly involved in cross-reactivity. Substituting three successive amino acids in these sites to triple alanine decreased IgE reactivity to the allergen. However, the degree of reduction in IgE reactivity largely depended on the site mutated and the serum used, suggesting that Can f 6 is a polyvalent allergen containing multiple epitopes and Can f 6-reactive sera contain varied amounts of IgE recognising individual Can f 6 epitopes including those predicted in this study. We also demonstrated that the predicted epitopes are partly involved in IgE cross-reactivity to Fel d 4. Interestingly, the effect of the mutation depended on whether the protein was structured or denatured, indicating that the bona fide tertiary structure of Can f 6 is essential in determining its IgE epitopes.