Lingonberry (Vaccinium vitis-idaea L.), small cranberry (Vaccinium microcarpum) and bigger cranberry (Vaccinium oxycoccos L.,) are popular berries in Nordic countries and Russia, which are used in gravies, dressing and pantry products. Furthermore, past few years cranberry/lingonberry products have been increasedly marketed as a natural solution to avoid recurrent urinary infections [1–4]. Cranberry/lingonberry juice or cranberry-concentrate tablets, which appear to inhibit the attachment of pathogens to uroepithelium [5, 6], have been incorporated to the prophylaxis of chronic urinary tract infections in elderly as well as the prophylaxis of recurrent acute uncomplicated urinary tract infection in sexually active women[2, 7].

We prepared a protein extract of 0.6 mg/ml in phosphate buffered saline using frozen lingonberries in the presence of protease inhibitors. After informed consent patient's serum was obtained. Two independent lingonberry allergen extract-coated IgE ELISAs using goat anti-human IgE-labelled-peroxidase (Sigma-Aldrich, ST Louis, MO, USA) showed positive results. (OD 495): 0.343 (patient) vs 0.017 (control) (Mean values from 2 different assays).

SDS-PAGE[8] was performed with a 12% polyacrylamide gel and a stacking gel of 4%. It was applied 19.2 μg of lingonberry extract to every lane and electrophoresis was performed (Mini Protean II System, Bio-Rad laboratories, Richmond, USA). Then, proteins were electrophoretically transferred from the separating gel to Immobilon-P™ (PVDF, Millipore Corporation, Billerica, MA, USA) membranes in a transfer buffer. After blocking with a solution of gelatine 3% for 1 hour, the membranes were washed and incubated overnight with patient's and normal control sera. Next day, membranes were washed and incubated with goat anti-human IgE-labelled-peroxidase as mentioned above. Detection was performed with a chemiluminescence substrate (Pierce Chemical Company, Rockford, Illinois). The western-blot revealed IgE in the patient's serum that bound to some medium/high-molecular-weight protein bands (Figure 1b). Control sera were negative.

Lingonberry's native home is in the woods of Norway, Sweden and Finland. The Nordic countries' people pick and use about 50 million kg of lingonberries per year[9], which they use in jams, jellies, preserves, concentrates, and liquors; the berries are also sold fresh. Interest of lingonberry in the possible health benefits is not only due to the inhibition of the attachment of pathogens to uroepithelium[5], but also to the total content of flavonoids, which is higher than that in the commonly consumed fruits or vegetables. Some flavonoids, such as quercetin[10], in which lingonberries are an excellent source, have potent antioxidant and free-radical scavenging activities observed in vitro. Some studies support a protective effect of flavonoid consumption in cardiovascular disease and cancer. Because there are many biological activities attributed to the flavonoids further studies in both the laboratory and clinic are running.

To the best of our knowledge, this is the first case reported of allergy to lingonberry. It is tempting to speculate that previous exposure by means of lingonberry products was sensitizing. The positive skin test, IgE-ELISA, western-blot and the symptoms and timing of the episode strongly implicate lingonberry. This report indicates that the lingonberry products might be allergenic when ingested. Further studies would be needed to characterize the allergenic component or components in lingonberry.