Methods: Birch pollen allergic patients and healthy control subjects were recruited. In vivo nasal pollen challenges were performed and nasal epithelial specimens were collected. A systems biology approach using a wealth of methods, including several microscopy techniques (light, confocal, immuno transmission electron [TEM]), transcriptomics (chips and massive parallel sequencing), mass spectrometry, immunohistology, in silico analyses were used.
Results: Already one minute after the birch pollen perturbation Bet v 1 was found both on cell surfaces as well as within villae, in cytoplasm, in intracellular vesicles, and also in nuclei of epithelial cells in allergic patients, but not in the healthy individuals. Anti-Bet v 1 stainings in conjunctival biopsies supported a very rapid traffic through the epithelium in allergic patients, but not in healthy subjects. A striking specificity is observed when birch pollen allergic subjects were also challenged with timothy grass pollen and no entry of this pollen allergen Phl p 1 into epithelial cells was detected. While the specific transport mechanism for birch pollen remains unsolved the first hints of the role of caveolae in this have been obtained. In the double immunoTEM analyses caveolin 2, but not caveolin 1 or 3, was present on the conjunctival epithelial surface in the same clusters as Bet v 1.
Transcriptomics indicated that the health epithelium displayed a strong immune response against pollen allergens while this response was absent in the epithelium of allergic patients.
Conclusions: Active transport of allergens through the epithelium might be incorporated to the pathogenesis of allergy. It is possible that the healthy epithelium displays a strong immune response against pollen allergens and thus escapes from becoming allergic. If allergy turns out to be, at least in part, a result of epithelial hyposensitivity, it could have major consequences in the strategies of prevention and treatment of these diseases. Towards this end, a national allergy program has been launched in Finland, which changes the basic idea of trying to avoid allergens to the concept of natural exposure and tolerance.