Structural homology of mite profilins to plant profilins is not indicative of allergic cross-reactivity.

Structural and allergenic characterization of mite profilins has not been previously pursued to a similar extent as plant profilins. Here, we describe structures of profilins originating from Tyrophagus putrescentiae (registered allergen Tyr p 36.0101) and Dermatophagoides pteronyssinus (here termed Der p profilin), which are the first structures of profilins from Arachnida. Additionally, the thermal stabilities of mite and plant profilins are compared, suggesting that the high number of cysteine residues in mite profilins may play a role in their increased stability. We also examine the cross-reactivity of plant and mite profilins as well as investigate the relevance of these profilins in mite inhalant allergy. Despite their high structural similarity to other profilins, mite profilins have low sequence identity with plant and human profilins. Subsequently, these mite profilins most likely do not display cross-reactivity with plant profilins. At the same time the profilins have highly conserved poly(l-proline) and actin binding sites.

Storage and release of hydrogen cyanide in a chelicerate (Oribatula tibialis).

Cyanogenesis denotes a chemical defensive strategy where hydrogen cyanide (HCN, hydrocyanic or prussic acid) is produced, stored, and released toward an attacking enemy. The high toxicity and volatility of HCN requires both chemical stabilization for storage and prevention of accidental self-poisoning. The few known cyanogenic animals are exclusively mandibulate arthropods (certain myriapods and insects) that store HCN as cyanogenic glycosides, lipids, or cyanohydrins. Here, we show that cyanogenesis has also evolved in the speciose Chelicerata. The oribatid mite Oribatula tibialis uses the cyanogenic aromatic ester mandelonitrile hexanoate (MNH) for HCN storage, which degrades via two different pathways, both of which release HCN. MNH is emitted from exocrine opisthonotal oil glands, which are potent organs for chemical defense in most oribatid mites.

Biosynthetic pathway of aliphatic formates via a Baeyer-Villiger oxidation in mechanism present in astigmatid mites.

Astigmatid mites depend on bioactive glandular secretions, pheromones, and defensive agents to mediate intra- and interspecies interactions. Aliphatic formates, such as (Z,Z)-8,11-heptadecadienyl formate (8,11-F17) and (Z)-8-heptadecenyl formate (8-F17), are rarely encountered natural products that are abundant in Sancassania sp. Sasagawa (Acari: Acaridae) mite secretions. Linoleic acid and oleic acid are predicted as key intermediates in the synthesis of the closely related aliphatic formates. To gain insight in this biosynthetic pathway, acarid mite feeding experiments were conducted using 13C-labeled precursors to precisely track incorporation. Analyses using 13C NMR spectroscopy demonstrated that the 13C-labeling pattern of the precursors was detectable on formates in exocrine secretions and likewise on fatty acids in total lipid pools. Curiously, the results demonstrated that the formates were biosynthesized without the dehomologation of corresponding fatty acids. Careful examination of the mass spectra from labeling experiments revealed that the carbonyl carbon of the formates is originally derived from the C-1 position of the fatty acids. Consistent with a Baeyer-Villiger oxidation reaction, labeling studies support the insertion of an oxygen atom between the carbonyl group and carbon chain. Empirical data support the existence of a Baeyer-Villiger monooxygenase responsible for the catalyzation of the Baeyer-Villiger oxidation. The predicted existence of a Baeyer-Villiger monooxygenase capable of converting aliphatic aldehydes to formates represents an exciting opportunity to expand the enzymatic toolbox available for controlled biochemical synthesis.

Mite allergen extracts and clinical practice.

OBJECTIVE: To provide physicians, researchers, and other interested health care professionals with information about how mite source materials and allergen extracts are manufactured, including the critical process parameters that can affect the final composition of allergenic extracts available for clinical use. DATA SOURCES: A PubMed search was performed using focused keywords combined with relevant regulatory documents and industry guidelines. STUDY SELECTIONS: The information obtained through literature and specialized books was evaluated and combined with the personal expertise and experience of the authors. RESULTS: Dermatophagoides farinae and Dermatophagoides pteronyssinus are the primary species responsible for allergen sensitizations and allergy symptoms in genetically predisposed individuals. Storage mites belonging to the families Glycyphagidae, Echimyopodidae, and Acaridae can also be relevant sources of indoor mite allergens. The cultivation and purification processes used to produce mite raw materials play a critical role in the final composition of mite allergen extracts. Mite extract standardization in the United States is based on total allergenic activity with respect to a single national standard, whereas in Europe consistency is ensured by in-house standards and international references. Because of the limitation of allergen avoidance and pharmacotherapy for patients with severe allergic rhinitis and asthma, house dust mite subcutaneous immunotherapy or sublingual immunotherapy can be an invaluable treatment option for them. CONCLUSION: Differences in manufacturing processes and extract standardization approaches may lead to differences in extract quality and potency. Physicians should be aware of these potential sources of mite extract variability. Use of well-standardized house dust mite extracts would be critical for success in the diagnosis and treatment of house dust mite allergy.

Evaluation of a novel automated allergy microarray platform compared with three other allergy test methods.

Microarray platforms, enabling simultaneous measurement of many allergens with a small serum sample, are potentially powerful tools in allergy diagnostics. We report here the first study comparing a fully automated microarray system, the Microtest allergy system, with a manual microarray platform, Immuno-Solid phase Allergen Chip (ISAC), and two well-established singleplex allergy tests, skin prick test (SPT) and ImmunoCAP, all tested on the same patients. One hundred and three adult allergic patients attending the allergy clinic were included into the study. All patients were tested with four allergy test methods (SPT, ImmunoCAP, Microtest and ISAC 112) and a total of 3485 pairwise test results were analysed and compared. The four methods showed comparable results with a positive/negative agreement of 81-88% for any pair of test methods compared, which is in line with data in the literature. The most prevalent allergens (cat, dog, mite, timothy, birch and peanut) and their individual allergen components revealed an agreement between methods with correlation coefficients between 0·73 and 0·95. All four methods revealed deviating individual patient results for a minority of patients. These results indicate that microarray platforms are efficient and useful tools to characterize the specific immunoglobulin (Ig)E profile of allergic patients using a small volume of serum sample. The results produced by the Microtest system were in agreement with diagnostic tests in current use. Further data collection and evaluation are needed for other populations, geographical regions and allergens.

Mass fingerprint analysis of spider mites (Acari) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for rapid discrimination.

RATIONALE: Discrimination of spider mite species is still performed using morphological information, although DNA and other biological approaches have been attempted for identification purposes. These techniques need much time, are expensive, and require specialist staff. As an alternative, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis is applied for rapid discrimination of spider mite species. METHODS: Spider mites were analyzed using MALDI-TOFMS after extraction with 70% formic acid and acetonitrile. A single spider mite was also analyzed directly on double-sided carbon tape. A dendrogram was compiled from the MS data. RESULTS: Evolutionarily close and morphologically similar spider mites, the Kanzawa (Tetranychus kanzawai) and the two-spotted (T. urticae) spider mites, as well as three other related species of spider mites, could be discriminated by mass fingerprints. Although female adults were mainly used in this report, male adults and nymphs showed almost the same mass fingerprints and were not considered to affect discrimination capability. A single spider mite on double-sided carbon tape was analyzed directly by MALDI-TOFMS. CONCLUSIONS: Spider mites could be analyzed directly by MALDI-TOFMS, with evolutionarily and morphologically closely related spider mites showing different mass fingerprints, allowing for their identification.

Taxonomic distribution of defensive alkaloids in Nearctic oribatid mites (Acari, Oribatida).

The opisthonotal (oil) glands of oribatid mites are the source of a wide diversity of taxon-specific defensive chemicals, and are likely the location for the more than 90 alkaloids recently identified in oribatids. Although originally recognized in temperate oribatid species, alkaloids have also been detected in related lineages of tropical oribatids. Many of these alkaloids are also present in a worldwide radiation of poison frogs, which are known to sequester these defensive chemicals from dietary arthropods, including oribatid mites. To date, most alkaloid records involve members of the superfamily Oripodoidea (Brachypylina), although few species have been examined and sampling of other taxonomic groups has been highly limited. Herein, we examined adults of more than 60 species of Nearctic oribatid mites, representing 46 genera and 33 families, for the presence of alkaloids. GC-MS analyses of whole body extracts led to the detection of 15 alkaloids, but collectively they occur only in members of the genera Scheloribates (Scheloribatidae) and Protokalumma (Parakalummidae). Most of these alkaloids have also been detected previously in the skin of poison frogs. All examined members of the oripodoid families Haplozetidae and Oribatulidae were alkaloid-free, and no mites outside the Oripodoidea contained alkaloids. Including previous studies, all sampled species of the cosmopolitan oripodoid families Scheloribatidae and Parakalummidae, and the related, mostly tropical families Mochlozetidae and Drymobatidae contain alkaloids. Our findings are consistent with a generalization that alkaloid presence is widespread, but not universal in Oripodoidea. Alkaloid presence in tropical, but not temperate members of some non-oripodoid taxa (in particular Galumnidae) deserves further study.

Chemical basis of unwettability in Liacaridae (Acari, Oribatida): specific variations of a cuticular acid/ester-based system.

Oribatid mites of the family Liacaridae comprise a large number of species with smooth and shiny body surfaces that display extraordinary anti-wetting properties. The principle of liacarid unwettability is not related to micro-structured surfaces as present in many Oribatida ("Lotus effect") but the formation of raincoat-like lipid layers covering the epicuticle. We here conducted a comparative study on the chemistry of cuticular lipid layers in a selection of Liacaridae, including representatives of all major Central European genera, Liacarus, Dorycranosus, Adoristes, and Xenillus. Cuticular lipids of unwettable individuals were removed from mite bodies by hexane extraction, and were analyzed by GC-MS. Basically, two chemically distinguishable systems were found. Type I: cuticular lipids of Liacarus subterraneus, L. coracinus, L. nitens, Dorycranosus curtipilis, and Xenillus tegeocranus contained different carboxylic acids (C8-, C10-, C10:1-, C10:2-acids) and their corresponding di-glycerides in species-specific combinations. Type II: Adoristes ovatus exhibited a system of cuticular lipids composed of esters of pentanoic- and heptanoic acids with C14-, C15-, C16- and C17-alcohols. Interestingly, the chemistry of surface lipids did not reflect the morphology of the cuticle in the species investigated. Smooth and shiny cuticles, though exhibiting a specific pattern of round or slit-like pores, were found in representatives of Liacarus, Dorycranosus (all of which exhibiting cuticular chemistry of type I) and Adoristes (exhibiting cuticular chemistry of type II). Xenillus, possessing a rough, cerotegumental cement layer-covered surface, showed type I-chemistry. The acid-esters systems herein investigated are considered characteristic for the cuticular chemistry of Liacaridae or a lineage of these, and provide first insights into the comparative chemistry of the inner (=lipid) layer of the oribatid cerotegument.

Cryptic diversity in host-associated populations of Tetra pinnatifidae (Acari: Eriophyoidea): what do morphometric, mitochondrial and nuclear data reveal and conceal?

Traditional morphology-based taxonomy of eriophyoid mites (Acari: Eriophyoidea) has been challenged by molecular-based technologies in the detection of cryptic species. However, the implications of such cryptic diversity appear to differ when methods based on different types of data are used. Here, samples of a host-associated eriophyoid mite species, Tetra pinnatifidae, collected from different host plants and localities are evaluated. The congruence of results based on morphometric (32 characters), mitochondrial (16S), and nuclear (28S) data were evaluated and showed a host-associated cryptic diversity dividing this morphospecies into several groups/clades that were morphometrically indistinguishable. In comparison, the 16S data confirmed cryptic speciation and intra-clade host-associated diversity, while 28S did not. In contrast, 28S data revealed potential gene flow between host-associated populations. High mitochondrial divergence, as well as low nuclear and morphological divergence indicated very recent stage of cryptic diversity of this eriophyoid mite.

Homologous Design and Three-Dimensional Quantitative Structure-Activity Relationship Study of Acaricidal 2,4-Diphenyloxazolines Containing Different Heteroatoms and Alkyl Chains.

In order to speculate the three-dimensional structure of the potential binding pocket of the chitin synthase inhibitor, a series of 2,4-diphenyloxazoline derivatives with different lengths of alkyl chains and heteroatoms were designed and synthesized by a homologous strategy. The bioassay results indicate that both the length of the alkyl chains and the type of substituents can affect the acaricidal activity against mite eggs. Compounds containing chloropropyl, alkoxyalkyl, and para-substituted phenoxyalkyl or phenylthioalkyl groups exhibit good activity, while those containing steric hindrance substituents or carbonyl substituents on the benzene ring exhibit reduced activity. Three-dimensional quantitative structure-activity relationship (3D-QSAR) study showed that there may be a narrow hydrophobic region deep in the pocket, and the steric effect plays a more important role than the electrostatic effect. The current work will provide assistance for future molecular design and target binding research.

From repulsion to attraction: species- and spatial context-dependent threat sensitive response of the spider mite Tetranychus urticae to predatory mite cues.

Prey perceiving predation risk commonly change their behavior to avoid predation. However, antipredator strategies are costly. Therefore, according to the threat-sensitive predator avoidance hypothesis, prey should match the intensity of their antipredator behaviors to the degree of threat, which may depend on the predator species and the spatial context. We assessed threat sensitivity of the two-spotted spider mite, Tetranychus urticae, to the cues of three predatory mites, Phytoseiulus persimilis, Neoseiulus californicus, and Amblyseius andersoni, posing different degrees of risk in two spatial contexts. We first conducted a no-choice test measuring oviposition and activity of T. urticae exposed to chemical traces of predators or traces plus predator eggs. Then, we tested the site preference of T. urticae in choice tests, using artificial cages and leaves. In the no-choice test, T. urticae deposited their first egg later in the presence of cues of P. persimilis than of the other two predators and cue absence, indicating interspecific threat-sensitivity. T. urticae laid also fewer eggs in the presence of cues of P. persimilis and A. andersoni than of N. californicus and cue absence. In the artificial cage test, the spider mites preferred the site with predator traces, whereas in the leaf test, they preferentially resided on leaves without traces. We argue that in a nonplant environment, chemical predator traces do not indicate a risk for T. urticae, and instead, these traces function as indirect habitat cues. The spider mites were attracted to these cues because they associated them with the existence of a nearby host plant.

Alkaloids in the mite Scheloribates laevigatus: further alkaloids common to oribatid mites and poison frogs.

Poison frogs are chemically defended from predators by diverse alkaloids, almost all of which are sequestered unchanged from alkaloid-containing arthropods in the frog diet. Oribatid mites recently have been proposed as a major dietary source of poison frog alkaloids. Here, we report on alkaloids common to an oribatid mite and poison frogs. Gas chromatographic-mass spectrometric analysis of methanol extracts of adult Scheloribates laevigatus (Oribatida: Scheloribatidae) revealed nine alkaloids. Five of these have been detected previously in the skin glands of poison frogs: two isomers of the pumiliotoxin 291G, two isomers of the 5,6,8-trisubstituted indolizidine 209C, and the 5,6,8-trisubstituted indolizidine 195G. The other four alkaloids, a pumiliotoxin, a tricyclic (coccinelline-like), and two isomers of an izidine, were not previously known, but are similar in structure to alkaloids found in poison frogs. Alkaloids were not detected in immature S. laevigatus, suggesting that they are adult-specific and possibly the result of mite biosynthesis. Although most of the alkaloids detected in S. laevigatus are common to poison frogs, the geographic distributions of these organisms are not sympatric. The findings of this study indicate that oribatid mites, and in particular, members of the genus Scheloribates, represent a relatively unexplored arthropod repository for alkaloids and a significant dietary source of alkaloids in poison frogs.

Discrimination of Oribotritia species by oil gland chemistry (Acari, Oribatida).

The chemical composition of secretions from opisthonotal (oil) glands in four species of the oribatid mite genus Oribotritia (Mixonomata, Euphthiracaroidea, Oribotritiidae) was compared by means of gas chromatography--mass spectrometry. The secretions of all, O. banksi (from North America) and three Austrian oribotritiids (O. berlesei, O. hermanni, O. storkani), are shown to be based on certain unusual compounds, the iridoid monoterpenes chrysomelidial and epi-chrysomelidial and the diterpene ß-springene. These components probably represent general chemical characteristics of oribotriid oil glands. Their relative abundance in the secretions along with further components (mainly saturated and unsaturated C(13)-, C(15)-, C(17)-hydrocarbons, and the tentatively identified octadecadienal) led to well-distinguishable, species-specific oil gland secretions profiles. In addition a reduced set of "Astigmata compounds" (sensu Sakata and Norton in Int J Acarol 27:281-291, 2001)--namely the two monoterpenes neral and geranial--could be detected in extracts of O. banksi nevertheless indicating the classification of euphthiracaroids within the (monophyletic) group of "Astigmata compounds-bearing"-Oribatida. These compounds are considered to be apomorphically reduced in all Austrian species. Our findings emphasize the potential of chemosystematics using oil gland secretion profiles in the discrimination of morphologically very similar, syntopically living or even cryptic oribatid species.

Describing fluctuating indoor aerosol dust measurements with application to house dust mite allergens.

Measuring house dust mite aeroallergen concentrations is essential in understanding mite allergen exposure. Physically, the aerolized house dust mite faeces are part of indoor particulate matter. We studied the statistical ways of summarizing measurements of fluctuating mite aeroallergen exposure inside homes through indoor particulate matter. To study emissions from beddings, we measured the time-related airborne dust concentration after shaking a duvet. Analysis was performed both by a method based on the estimated mean and by a non-linear model. Twenty-eight studies reported a sum of concentrations; only one also reported the peak. In our four experiments on shaking a duvet (245 to 275 measurements each), the peak value was two to four times higher than the mean. The mean-based and non-linear models both predicted the sum of concentrations exactly. A 1% upper prediction bound and the non-linear model predicted the peak emission rate moderately well (64 to 92%, and 63 to 93%, respectively). Mean levels of indoor particulate matter measurements differ substantially from peak concentrations. The use of the mean is only sufficient to predict the sum of concentrations. We suggest that, mite aeroallergen measurements should include information on the peak as well as the mean.

Characterization of the immune response of domestic fowl following immunization with proteins extracted from Dermanyssus gallinae.

Dermanyssus gallinae is the most significant ectoparasite of European poultry egg laying production systems due to high costs of control and associated production losses as well as adverse effects on bird welfare. In this study, soluble proteins were extracted from unfed D. gallinae (DGE) using a urea-based detergent and ultra-filtration, passed through a 0.22 microm filter and blended aseptically with adjuvant. One group of laying hens was immunized with DGE and adjuvant (Montanide ISA 50 V) whilst another group (Control) received physiological saline and adjuvant. All birds were immunized on two occasions, 21 days apart. Antibody response to immunization was determined by ELISA and western blotting using immunoglobulins (Igs) extracted from egg yolk. DGE immunization of hens resulted in a significant (P<0.05) IgY response compared to controls, although there was no significant difference in IgM response between treatments. A number of proteins were identified by western blotting using IgY antibodies from DGE immunized birds, most prominently at 40 and 230kDa. Analysis of proteins from approximately corresponding bands on SDS-PAGE confirmed the identity of tropomyosin, whilst other proteins showed high sequence homology with myosin and actin from other arachnid and insect species. Immunization of hens with DGE resulted in a 50.6% increase in mite mortality (P<0.001) 17h after feeding when tested by an in vitro mite feeding model. Data in this study demonstrate that somatic antigens from D. gallinae can be used to stimulate a protective immune response in laying hens. Further work is needed to identify other proteins of interest that could confer higher protection against D. gallinae, as well as optimization of the vaccination and in vitro testing protocol.

Wearing a raincoat: exocrine secretions contain anti-wetting agents in the oribatid mite, Liacarus subterraneus (Acari: Oribatida).

Liacarus subterraneus is a large, soil-dwelling oribatid mite species that possesses a conspicuously shiny, clean and not wettable cuticular surface. The exocrine cuticular chemistry of this species was investigated by means of gas chromatography-mass spectrometry. Besides a fraction of hydrocarbons and a terpene, hexane extracts of whole mite bodies exhibited free carboxylic acids and their glycerides as main components. The compounds were arranged in three distinct extract profiles. Based on data from individual extracts, (1) the majority (more than 3/4) of specimens showed large amounts of 1,2-dioctanoyl-glycerol (and three other related esters) but no (or only traces of) free carboxylic acids. (2) In about 1/8 of extracts, free acids (mainly octanoic (caprylic) acid) and glycerides were detected. This second type of profile highly varied with respect to the relative abundance of acids and esters. (3) The third profile (in about 7% of specimens) exclusively exhibited free acids and no (or only traces of) glycerides. In addition, a few extracts exhibited no components at all. The extract compounds most likely originate from the lipid layer of the cerotegument of L. subterraneus. The cuticle of individuals that possessed extractable cerotegumental compounds (profile I, II, III) exhibited strong water repellent properties, while the cuticle of individuals that possessed no components in their extract did not. After hexane extraction, water repellent properties got lost. The distinct extract profiles detected most likely portray the stepwise generation of an anti-wetting, exocrine surface lipid layer of glycerides: If this layer is lost, fatty acids may be discharged again (profile III) and may subsequently esterify (profile II) to larger and more stable esters (diacyl-glycerols), eventually building up the "raincoat" (mainly profile I) of L. subterraneus.

Chitin in the peritrophic membrane of Acarus siro (Acari: Acaridae) as a target for novel acaricides.

The peritrophic membrane in Acarus siro L. (Acari: Acaridae) is produced by distinct cells located in the ventriculus. In this study, the chitin inside the peritrophic membrane was detected using wheat germ-lectin conjugated with colloidal gold (10 nm). The chitin fibrils of the peritrophic membrane were a target for chitin effectors, including 1) chitinase, which hydrolyzes chitin fibers inside the peritrophic membrane; 2) calcofluor, which binds to chitin and destroys the peritrophic membrane mesh structure; and 3) diflubenzuron, which inhibits chitin synthesis. In addition, soybean trypsin protease inhibitor (STI) and cocktails of chitinase/calcofluor, diflubenzuron/calcofluor and chitinase/STI were tested. These compounds were supplemented in diets and an increase of population initiated from 50 individuals was observed after 21 d of cultivation. Final A. siro densities on experimental and control diets were compared. The chitin in the peritrophic membrane was determined to be a suitable target for novel acaricidal compounds for suppressing the population growth of A. siro. The most effective compounds were calcofluor and diflubenzuron, whereas the suppressive effects of chitinase and STI were low. The failure of chitinase could be due to its degradation by endogenous proteases. The combination of chitinase and STI suppressed A. siro population growth more effectively than when they were tested in oral admission separately. The combinations of calcofluor/chitinase or calcofluor/difluorbenzuron showed no additive effects on final A. siro density. The presence of chitin in peritrophic membrane provides a target for novel acaricidal compounds, which disrupt peritrophic membrane structure. The suitability of chitin effectors and their practical application in the management of stored product mites is discussed.

Effects of acetamiprid on life cycle development of predatory mite Amblyseius cucumeris (Acari: Phytoseiidae) after contact exposure.

Amblyseius cucumeris (Oudemans) is a beneficial non-target arthropod (NTA) and a key predator of pest mites in integrated pest management (IPM) programs across china. The toxic effects of insecticides have been extensively reported on predatory mites, but few studies devoted to the toxicity of compounds to A. cucumeris. In this study, the effects of a single application of acetamiprid against the A. cucumeris were investigated in a 48-h acute and a 30-d chronic test. In both tests the insecticide acetamiprid was applied once. In the acute test, the "open glass plate method" was used, with a 48-h LC50 value of 223.6 (149.8-336.9) mg a. i. L-1 for adult female. The LC50 was 1.49-fold the Maximum field recommended concentration. In the chronic test, exposure concentrations (1.12, 2.24, 4.47, 8.94, and 22.4 mg a. i. L-1) were designed based on a preliminary 48-h LC50 value for adult female. Above treatment levels of 2.24-4.47 mg a. i. L-1 reduce the total development time, survival rates and food consumption of A. cucumeris in different development stages. In addition, at acetamiprid concentrations higher than 2.24 mg a. i. L-1 serious effect on the capacity of oviposition of female adults were observed. However, even the highest treatment level of 22.4 mg a. i. L-1 did not affect egg hatching rates of exposed eggs. Acetamiprid had significant adverse effects on different development life stages of A. cucumeris. The results provide informative data for implementing biological and chemical control strategies in integrated pest management of spider mites.

The Blomia tropicalis allergens.

Blomia tropicalis allergens are the most important mite allergens in tropical regions. Most of them only have 30-40% sequence identity with their Dermatophagoides counterparts and they share low IgE cross reactivity and exhibit different immunobiology. Unlike the pyroglyphid counterparts, Blo t 5 is the major allergen whereas Blo t 1 only has modest allergenicity.

Comparative analysis of the frequency of house dust mite specific and nonspecific Th1 and Th2 cells in skin lesions and peripheral blood of patients with atopic dermatitis.

Until recently it was believed that the T cell response of atopic dermatitis patients challenged with inhalant allergens originates almost exclusively and specifically from Th2 cells capable of secreting an abundance of interleukin (IL)-4 while producing no interferon (IFN)-gamma. To reevaluate this concept in a large cohort of atopic dermatitis patients we established 177 CD4+ T cell clones (45 of which showed specificity for house dust mite antigen) from the peripheral blood (n = 76), naturally occurring skin lesions (n = 40), and allergen-exposed skin (n = 61) of different patients. These clones were examined for their capacity to secrete IL-4 and IFN-gamma upon mitogenic stimulation. Moreover, 20 of these T cell clones were investigated for the synthesis of transcripts for IL-5, another Th cytokine. Our results indicate that the majority (52-100%) of allergen-specific T cells in both skin and blood of atopic individuals failed to exhibit a restricted cytokine secretion pattern and thus were classified as Th0 cells. House dust mite antigen specific T cells displaying a restricted secretion pattern (n = 16) were either of the Th1 or the Th2 type. Specific Th2 cells, however, were found almost exclusively in allergen patch test reactions, indicating that the Th2 differentiation pathway is seen preferentially in allergen-exposed skin. The cytokine secretion profile of T cell clones obtained from naturally occurring skin lesions showed similarity to those of patch test lesion, suggesting that the patch test represents a useful model to investigate the pathogenesis of atopic dermatitis.