Allergenic molecules
At the time of writing, 11 German cockroach allergens have been identified (13). The biochemical properties, molecular mass and IgE prevalence of the German cockroach allergens are summarized below (1, 13, 14).
Allergen |
Biochemical property |
Molecular Weight (kDa) |
IgE prevalence (%) |
---|
Bla g 1 |
Nitrile specifier, microvilli-like protein (function currently unknown) |
46 |
20-40 |
Bla g 2 |
Inactive aspartic protease |
36 |
40-70 |
Bla g 3 |
Hemocyanin, Arylphorins/arthropod hemocyanins |
79 |
22 |
Bla g 4 |
Calycin, lipocalin |
21 |
17-40,53 |
Bla g 5 |
Glutathione S-transferase (GST) |
23 |
35-68 |
Bla g 6 |
Troponin C |
21 |
14 |
Bla g 7 |
Tropomyosin |
33 |
18-31 |
Bla g 8 |
Myosin light chain |
21 |
14 |
Bla g 9 |
Arginine kinase |
40 |
35-50 |
Bla g 11 |
Alpha-amylase |
57 |
41 |
Bla g 12 |
Chitinase |
58 |
17 |
Allergen |
Biochemical property |
Molecular Weight (kDa) |
IgE prevalence (%) |
---|
Cross-reactivity
Bla g 1
A key German cockroach allergen, Bla g 1 has demonstrated allergenic cross-reactivity with Per a 1, an American cockroach allergen (15, 16). Bla g 1 and Per a 1 share approximately 70% of their amino acid identity (16). In addition, Bla g 1 has a primary structure homologous to the ANG12 protein which is produced post blood meal by female mosquitos and microvilli-like proteins common to other insects (17).
Bla g 4
Bla g 4 is a calycin which belongs to the family of proteins known as lipocalins and this group of proteins includes some major allergens for example, beta-lactoglobulin found in cow milk, and proteins found in urine excreted by rats and mice (18, 19). The homology of the amino acid sequence for these proteins is relatively low of around 20%. However, calycin proteins are known to cause IgE antibody responses when inhaled or ingested and for this reason are linked to asthma and food allergies (19).
Bla g 5
Bla g 5 is a glutathione S-transferase (GST) sharing an amino acid sequence identity of approximately 42-51% to the GST-2 subfamily from insects (20). Likewise, the sheep scab mite, Psoroptes ovis and house dust mite, Dermatophagoides pteronyssinus share homology with the GST allergen found in the German cockroach (21).
Bla g 7
Bla g 7 is an allergen belonging to the tropomyosin protein family. Tropomyosin is an allergen found in muscle of numerous animal species. It was first identified as a key allergen found in shrimp however, it is also found in mollusks, arthropods and parasites (20). There is a high level of homology (approximately 80%) between invertebrate tropomyosins resulting in antigenic cross-reactivity. There is reduced cross-reactivity among vertebrate and invertebrate tropomyosins because they have a lower homology (approximately 55%) (20). In fact, despite tropomyosins being highly conserved proteins within the animal kingdom, only invertebrate tropomyosins are allergenic and vertebrate are considered to be non-allergenic (22).
A study published by Jeong et al. (2004) concluded that tropomyosin was a key allergenic component responsible for the cross-reactivity between cockroaches and dust mites (23).
With shellfish allergy affecting approximately 2% of the world population, obtaining a diagnosis can be challenging due to the IgE cross-reactivity of tropomyosin found in a wide range of invertebrate including mites and cockroaches. Approximately 56% of shrimp IgE epitopes were conserved in cockroach species (24). An Immune Epitope Database and Analysis Resource, an epitope conservation model has been developed (24) which could be useful in the future for identifying cross-reactivity in patients.