Allergenic molecules
The recognition of HDM-specific allergens helps in the diagnosis and treatment of allergic diseases, associated with HDM, especially identification and characterization of novel HDM allergens (21). The allergens of D. farinae listed in the WHO/IUIS database include (22).
| Allergen | Biochemical name | Molecular Weight (kDa) | Allergenicity |
|---|---|---|---|
| Der f 1 | Cysteine protease | 27 |
|
| Der f 2 | NPC2 family | 15 |
|
| Der f 3 | Trypsin | 29 | |
| Der f 4 | Alpha-amylase | 57.9 | |
| Der f 5 | Low molecular weight IgE binding protein | 15.5 | |
| Der f 6 | Chymotrypsin | 25 | |
| Der f 7 | Bactericidal permeability-increasing like protein | 30-31 | |
| Der f 8 | Glutathione S-transferase | 32 | |
| Der f 10 | Tropomyosin | 37 |
|
| Der f 11 | Paramyosin | 98 |
|
| Der f 13 | Fatty acid binding protein | 15 | |
| Der f 14 | Apolipophorin | 177 | |
| Der f 15 | Chitinase | 98/109 | |
| Der f 16 | Gelsolin/villin | 53 | |
| Der f 17 | Calcium-binding protein | 53 | |
| Der f 18 | Chitin-binding protein | 60 | |
| Der f 20 | Arginine kinase | 40 | |
| Der f 21 | Not determined | 14 | |
| Der f 22 | Not determined | 14.7 | |
| Der f 23 | Peritrophin-like protein | 19 |
|
| Der f 24 | Ubiquinol-cytochrome c reductase binding protein hom*ologue | 13 | |
| Der f 25 | Triosephosphate isomerase | 34 | |
| Der f 26 | Myosin alkali light chain | 18 | |
| Der f 27 | Serpin | 48 | |
| Der f 28 | Heat Shock Protein | 70 | |
| Der f 29 | Peptidyl-prolyl cis-trans isomerase (cyclophilin) | 15 | |
| Der f 30 | Ferritin | 15 | |
| Der f 31 | Cofilin | 15 | |
| Der f 32 | Secreted inorganic pyrophosphatase | 35 | |
| Der f 33 | Alpha-tubulin | 52 | |
| Der f 34 | Enamine/imine deaminase | 16 | |
| Der f 35 | Not determined | 14.4 | |
| Der f 36 | Not determined | 23 | |
| Der f 37 | Chitin binding protein | 29 | |
| Der f 38 | Bacteriolytic enzyme | 15 | |
| Der f 39 | Troponin C | 18 |
Der f: Dermatophagoides farinae; IgE: Immunoglobulin E; RAST: Radioallergosorbent; ELISA: Enzyme-linked immunosorbent assay; SPT; Skin prick test.
The prevalence of IgE reactivity was observed to be 94.7%, of the total HDM extract, in a study conducted on 129 HDM-allergic Korean patients. It was reported that 79.1% of patients showed specific IgE to Der f 1 and Der f 2. Further, 9.3%, 6.2%, 7%, and 7% of patients showed IgE reactivities to Der f 6, Der f 8, Der f 10, and Der f 20, respectively. In HDM-allergic patients having respiratory allergy and AD, Der f 2 was the most sensitized allergen. Further, the diagnostic sensitivity was reported to be increased with the combination of the group 1 (Der f 1) and 2 (Der f 2) major allergens (28).
Apart from the WHO/IUIS list, another allergen of D. farinae, Der f Alt a 10 has been described by a study. According to the findings reported in this study, 32.7% of AD patients were sensitized to Der f Alt a 10, in comparison to 3.0% in patients with allergic asthma/AR (29).
Cross-reactivity
The allergic sensitivity, following the ingestion of HDMs, show symptoms in two different forms - the ingestion of invertebrates demonstrating cross-reactivity with mite allergens, and the ingestion of foods that are contaminated with dust mites (1).A high degree of cross-reactivity is noted between D. pteronyssinus and D. farinae extracts, however, the reactivity between Dermatophagoides and B. tropicalis has been reported to be low (5).
According to a study, co-sensitization and cross-reactivity has been reported between B. tropicalis and two Dermatophagoides species, i.e., Der p and Der f. In this study, 70.14% of allergenic patients (1050 out of 1497 patients) were found to be co‐sensitized to B. tropicalis, Der p, and Der f. However, the cross-reactivity between B. tropicalis and Dermatophagoides was limited (30).
The structural similarities between Der p 1 and Der f 1 was demonstrated with an X-ray crystal structure analysis. The analysis showed a surface conservation of a crystal structure of natural Der f 1 with Der p 1, having 71% of amino acid similarity, along with an overlapping catalytic area.This high structural similarity observed between Der p 1 and Der f 1 are commonly believed to be the basis for their cross-reactivity (31, 32).
A high degree of cross-reactivity has also been reported between Der p 2 and Der f 2 (from D. farinae) (33).
Group 11 allergens (Der p 11, Der f 11) are considered as major allergen molecules in patients with AD, having sensitization to HDM, and thus should be included among allergen components for the routine testing in the clinical laboratory (34).
A high amino acid sequence similarity has been found between Der p 23 and Der f 23 (87%). Different structural studies of Der p 23 and consecutive modelling of Der f 23 on its structure, might imply on the occurrence of considerable cross-reactivity between the two proteins (35).
Der f 10 (tropomyosin from Der f) and Der p 10 of HDM, both are found be cross-reactive with Lep d 10 (tropomyosin from the storage mites), due to high level of hom*ology (36).
Tropomyosins are a large family of heat-resistant, alpha-helical proteins. These proteins form a coiled-coil structure of two parallel helices, that includes two sets of seven alternating actin-binding sites. This feature plays a vital role in regulating the function of actin filaments (37).
One of the most important cause of cross-reactivity, among mites, shellfish, helminths, and co*ckroaches is the Tropomyosin, although glutathione transferase may also be included. In cases where genuine sensitization is unclear, specific allergen components can be useful to identify primary allergy (5).
Tropomyosin allergens from HDMs are reported to show cross-reactivity with tropomyosin allergens of invertebrates, such as crustaceans (shrimp, lobster, crab, crayfish), mollusks (mussel, oyster, scallop, clams, abalone, snails, squid, octopus, cuttlefish) and insects (co*ckroaches) (1, 37).
Der f 10 allergen has shown sequence similarity with shrimp tropomyosin Pen a 1, American co*ckroach tropomyosin Per a 7, and lobster tropomyosin Hom a 1 (38).
Further, cross-reactivity has been reported between HDM and shrimp-reactive IgE antibodies, in patients with shrimp allergy (39). In patients with allergy to HDMs, reactivity to shrimp has also been revealed, especially in patients who were never been exposed to shrimps, because of religious dietary habits (40).
