Nitric oxide (NO) is present in air derived from the nasal airways. However, the precise origin and physiological role of airway-derived NO are unknown. We report that NO in humans is produced by epithelial cells in the paranasal sinuses and is present in sinus air in very high concentrations, close to the highest permissible atmospheric pollution levels. In immunohistochemical and mRNA in situ hybridization studies we show that an NO synthase most closely resembling the inducible isoform is constitutively expressed apically in sinus epithelium. In contrast, only weak NO synthase activity was found in the epithelium of the nasal cavity. Our findings, together with the well-known bacteriostatic effects of NO, suggest a role for NO in the maintenance of sterility in the human paranasal sinuses.

Current forms of allergy diagnosis and specific immunotherapy are performed with allergen extracts. Allergen extracts contain a variety of allergenic and nonallergenic components and their allergen content is often cumbersome to standardize. If used for diagnostic purposes, positive reactions to a given allergen extract will thus provide the information that an allergic subject is sensitized against extract components, but without identifying them. Likewise, extract-based immunotherapy cannot be adapted to the individual patient's sensitization pattern. Here we review progress in the field of molecular allergen characterization by recombinant DNA technology, leading to novel forms of component-resolved diagnostics (CRD) and immunotherapy (CRIT) based on recombinant allergens. Several studies have demonstrated advantages of recombinant allergenbased diagnosis. Using recombinant allergens in in vitro diagnostic devices, a patient's individual IgE reactivity profile can be quantitatively established. The presence of IgE to cross-reactive allergen components can thus be determined and used to predict clinically relevant sensitization to allergen sources which contain immunologically related allergens. Moreover it has been demonstrated that cocktails of recombinant allergens, matching the IgE epitope complexity present in natural allergen extracts, can be assembled. Component-resolved diagnosis will thus allow the precise selection of those molecules for specific immunotherapy to which a patient is actually sensitized. Recently, several recombinant hypoallergenic allergen derivatives have been developed for immunotherapy. The progress in allergen research achieved by the use of recombinant DNA technology holds promise that component-resolved diagnosis and immunotherapy may help refine the procedures of allergy diagnosis and immunotherapy in the coming decade and beyond.

Grass pollens are one of the most important airborne allergen sources worldwide. About 20 species from five subfamilies are considered to be the most frequent causes of grass pollen allergy, and the allergenic relationships among them closely follow their phylogenetic relationships. The allergic immune response to pollen of several grass species has been studied extensively over more than three decades. Eleven groups of allergens have been identified and described, in most cases from more than one species. The allergens range from 6 to 60 kD in apparent molecular weight and display a variety of physicochemical properties and structures. The most complete set of allergens has so far been isolated and cloned from Phleum pratense (timothy grass) pollen. Based on the prevalence of IgE antibody recognition among grass pollen-sensitized individuals, several allergens qualify as major, but members of two groups, groups 1 and 5, have been shown to dominate the immune response to grass pollen extract. Isoform variation has been detected in members of several of the allergen groups, which in some cases can be linked to observed genetic differences. N-linked glycosylation occurs in members of at least three groups. Carbohydrate- reactive IgE antibodies have been attributed to grass pollen sensitization and found to cross-react with glycan structures from other allergen sources, particularly vegetable foods. Another cause of extensive cross-reactivity are the group 12 allergens (profilins), which belong to a family of proteins highly conserved throughout the plant kingdom and present in all tissues. Members of eight allergen groups have been cloned and expressed as recombinant proteins capable of specific IgE binding. This development now allows diagnostic dissection of the immune response to grass pollen with potential benefits for specific immunotherapy.

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Type I allergy is an immunoglobulin E (IgE)-mediated hypersensitivity disease affecting more than 25% of the population. Currently, diagnosis of allergy is performed by provocation testing and IgE serology using allergen extracts. This process defines allergen-containing sources but cannot identify the disease-eliciting allergenic molecules. We have applied microarray technology to develop a miniaturized allergy test containing 94 purified allergen molecules that represent the most common allergen sources. The allergen microarray allows the determination and monitoring of allergic patients' IgE reactivity profiles to large numbers of disease-causing allergens by using single measurements and minute amounts of serum. This method may change established practice in allergy diagnosis, prevention, and therapy. In addition, microarrayed antigens may be applied to the diagnosis of autoimmune and infectious diseases.