Global (80mer) and local (8mer) identities found for the putative insect allergens.
Allergic manifestations to the ingestion of edible insects have been reported, especially in countries where edible insects are traditionally consumed. However, to date, allergens of edible insects have been poorly investigated. The AllergenOnline server was used for assessing the allergenic character of the putative IgE-binding cross-reactive allergens from the consumed yellow mealworm, silkworm, house fly maggot, migratory locust, house cricket, greater wax moth, black soldier fly, American grasshopper and Indian mealmoth. Positive hits correspond to allergens exhibiting >35% identity over an 80-residue sliding window and 100% identity over an 8-residue sliding window, respectively. Most of the hits consist of allergens from arthropods such as dust mites, crustaceans and insects, and more rarely, of allergens from mollusks, nematodes, and fungi. All the identifed allergens share conserved amino acid sequences and three-dimensional structures. Accordingly, the allergens of edible insects form clusters closely related to crustacean, mollusk and nematode clusters into the phylogenetic trees built up from the sequence alignments. Our computational investigations suggest edible insects possess a large repertoire of IgE-binding allergens they share with phylogenetically related groups of arthropods, mollusks, and nematodes. These cross-reacting allergens are susceptible to trigger allergic reactions in individuals previously sensitized to shellfish or mollusks.
- allergen repertoire
- edible insects
- dust mites
- IgE-binding cross-reactivity
The rapidly expanding world population, which is estimated to reach 9 billion people on 2040, underlines the urgent need to develop new sources of food proteins as a complement for the traditionally consumed proteins of plant and animal origin [1–3]. Among the new sources of food and feed proteins, insect proteins appear as a valuable candidate with respect to their good nutritional value for humans and animals  and their ability to be produced at a very large industrial scale . However, insect proteins have to be checked for food and feed security before the launching of any large-scale production [6–9]. In this respect, both the chemical (heavy metal and pesticide contamination) and biological safeties including the potential parasitic microbial and parasitic load, and the potential allergenicity, should be evaluated. Depending on the forthcoming predictable introduction of edible insect proteins in both the human and cattle diets, the potential allergic risk associated to the consumption of edible insects has been stressed out, due to the occurrence in insects of pan-allergens common to arthropods, mollusks, and nematodes [8–10]. To date, however, our knowledge on the diversity of insect allergens remains too limited to properly address the potential allergic risk associated to entomophagy, especially for people living in European countries where insect consumption is not a part of their eating habits. In the present chapter, we report the results of a bioinformatic approach aimed at filling the gaps in our existing knowledge about the variety of allergens occurring in some edible insect species.
2. Assessing the complexity of the IgE-binding allergen repertoire of edible insects
A bioinformatic approach based on the AllergenOnline server (
|Insect||Putative allergen||(No. hits 80mer)||(No. hits 8mer)|
|Sarcoplasmic Ca-binding protein||4||6|
|Sarcoplasmic Ca-binding protein||0||0|
|Acheta domesticus||Triosephosphate isomerase||4||27|
|Galleria mellonella||Glutathione S-transferase||3||22|
|Schisto americana||Arginine kinase||14||1383|
3. IgE-binding allergens of edible insects belong to conserved protein families
Bioinformatic investigations using a sliding window of 80 amino acids resulted in a large number of positive hits for the putative allergen proteins of all the insect species, with the exception of actin, sarcoplasmic Ca-binding protein (SCBP), and β-tubulin (Table 1). However, some of the global identities do not necessarily coincide with local identities, since no hit was found with a more restricted sliding window of eight amino acid residues. Both global and local identities were found with the thioredoxin allergen of silkworm, house fly maggot, and the Indian mealmoth (P. interpunctella).
Most of the hits found with the 80mer and 8mer windows consist of allergens from arthropods such as dust mites, crustaceans, and insects and, more rarely, of allergens from mollusks, nematodes, and fungi (Alternaria alternata, Aspergillus oryzae, Aspergillus fumigatus, Cladosporium herbaceum, Malassezia sympodialis) (Table 2). For a limited number of putative insect allergens like the widely distributed heat shock protein HSP 70, serine protease, trypsin, triosephosphate isomerase (TPI), and thioredoxin, hit allergens of plant (the blue cypress Cupressus arizonica, the maize Zea mays, the wheat Triticum aestivum, the common ragweed Ambrosia artemisiifolia, the olive tree Olea europaea) and animal (the Mozambique tilapia Oreochromis mossambicus, the dog Canis familiaris) origin were identified. Obviously, these allergens consist of ubiquitous pan-allergens that occur in so distantly phylogenetically related or phylogenetically unrelated organisms.
|Protein family||Insects||Dust mites||Crustaceans||Mollusks/Nematodes|
|Alpha-amylase||Bla g 11||Blo t 4||–||–|
|Per a 11||Der f 4|
|(+2)||Der p 4|
|Eur m 4 (+2)|
|Arginine kinase||Bomb m 1||Der f 20||Cra c 2||(4)|
|Per a 9||Der p 20 (+3)||Lit v 2|
|Plo i 1 (+5)||Pen m 2 (+23)|
|Chitinase||Per a 12 (+1)||Der f 15 (+5)||–||–|
|Glutathione||Bla g 5 (+1)||Blo t 8||–||–|
|S-transferase||Der f 8||Asc l 13 (N)|
|Der p 8 (+6)||Asc s 13 (N)|
|HSP 70 (heat shock protein)||Aed a 8 (+2)||Der f 28||–||–|
|Tyr p 28|
|Hemocyanin||Bla g 3||–||(1)||–|
|Per a 3|
|Myosin||Bla g 8 (+1)||Der f 26||Art fr 5||–|
|Cra c 5||–|
|Hom a 3|
|Lit v 3|
|Pen m 3 (+1)|
|Sarcoplasmic Ca-binding protein||Aed a 5 (+2)||–||Cra c 4||–|
|Eri s 4|
|Lit v 4|
|Mac r 4|
|Pen m 4|
|Pon l 4 (+24)|
|Serine protease||Api m 7||Der f 6||–||–|
|Bom t 4||Der p 6|
|Per a 10||Eur m 1 (+12)|
|Triosephosphate isomerase||Pol d 4|
|Pol e 4 (+14)|
|Tropomyosin||(2)||Der f 25||Arc s 8, Cra c 8||–|
|Aed a 10||Blo t 10||Cha f 1||Ani s 3 (N)|
|Bla g 7||Cho a 10||Cra c 1||Asc l 3 (N)|
|Chi k 10||Der f 10||Hom a 1||Hel as 1 (+50)|
|Lep s 1||Der p 10||Lit v 1|
|Per a 7 (+29)||Lep d 10||Mac r 1|
|Tyr p 10 (+11)||Mel l 1|
|Met e 1|
|Pan s 1|
|Pen a 1|
|Pen m 1|
|Por p 1 (+54)|
|Troponin C||Bla g 6, Per a 6||Tyr p 34||Cra c 6|
|Hom a 6||(1 N)|
|Pen m 6 (+2)|
|Trypsin||(4)||Blo t 3||–||–|
|Der f 3|
|Der p 3|
|Eur m 3|
|Tyr p 3 (+3)|
|Alpha-tubulin||–||Der f 33 (+2)||–||–|
All the insect allergens identified so far consist of proteins which belong to families of highly conserved proteins, namely, muscle proteins such as tropomyosin, myosin, and the sarcoplasmic Ca-binding protein and enzymes such as α-amylase, chitinase, glutathione S-transferase (GST), arginine kinase, serine protease, and trypsin. Most of these proteins have been already identified as allergens of both the German (Blattella germanica) and American cockroach (Periplaneta americana) (
3.1. Muscle proteins
The muscle proteins tropomyosin, myosin, and sarcoplasmic Ca-binding protein (SCBP) have been identified as major allergens of edible insects. Especially, tropomyosin appears as a major pan-allergen largely distributed among dust mites, insects, crustaceans, mollusks, and nematodes [12–16]. Major allergens of dust mites, e.g., Aca s 10 from Acarus siro, Blo t 10 from Blomia tropicalis, Der f 10 and Der p 10 from Dermatophagoides farinae and Dermatophagoides pteronyssinus, Gly d 10 from Glycyphagus destructor, Ixo sc 10 from the shoulder tick Ixodes scapularis, and Tyr p 10 from Tyrophagus putrescentiae, consist of tropomyosins (
Other muscle protein allergens like troponin and the sarcoplasmic Ca-binding protein (SCBP) also provide a number of allergens like the troponins Tyr p 24 from the dust mite T. putrescentiae, Bla g 6 and Per a 6 from the cockroaches B. germanica and P. americana, Cra c 6 and Pen m 6 from the shrimps C. crangon and P. monodon, Hom a 6 from the American lobster H. americanus, and the troponin of the nematode A. simplex (
All of these muscle protein allergens display a rather high resistance to both the proteolysis and heat denaturation, as exemplified by the experiments performed on the tropomyosin of different species of mealworm  and the oyster Crassostrea gigas .
A number of enzymes including hydrolases like α-amylase, chitinase, serine protease, and trypsin and metabolic enzymes like arginine kinase (AK), glutathione S-transferase (GST), and triosephosphate isomerase (TPI) have been identified as cross-reacting allergens of edible insects [11, 19–23].
Arginine kinase has been previously identified as a pan-allergen widely distributed in various insects such as the yellow mealworm (T. molitor) , the field cricket (Gryllus bimaculatus) , and the house cricket (A. domesticus) ; shrimps like the black tiger prawn (P. monodon) and the king prawn (Penaeus latisulcatus) ; the giant freshwater prawn (M. rosenbergii) [23, 25]; and crabs like the blue swimming crab (Portunus pelagicus)  and the red crab (c) . Arginine kinases consist of the major allergens Bla g 9 of the German cockroach (B. germanica) and Per a 9 of the American cockroach (P. americana) (
Alpha-amylase, a hydrolase of paramount importance for the digestion of starch by herbivorous and omnivorous organisms, occurs as an allergens in dust mites (Aca s 4 of A. siro, Blo t 4 of B. tropicalis, Der p 4 of D. pteronyssinus, Eur m 4 of Euroglyphus maynei, Tyr p 4 of T. putrescentiae) and insects (Sim v 3 and Sim v 4 of the striped black fly Simulia vittata, Bla g 11 and Per a 11 of the cockroaches B. germanica and P. americana) (
Other metabolic enzymes like the glutathione S-transferase GST (Aca s 8 of A. siro, Blo t 8 of B. tropicalis, Der f 8 and Der p 8 of D. farinae and D. pteronyssinus, Tyr p 8 of Tyroglyphus putrescentiae, Bla g 5 and Per a 5 of B. germanica and P. americana), chitinase (Blo t 15 of B. tropicalis, Der f 15 and Der p 15 of D. farinae and D. pteronyssinus, and Per a 12 of the cockroach P. americana), and triosephosphate isomerase TPI (Der f 25 of D. farinae, Bla g TPI of the cockroach B. germanica, For t TPI of the biting midge Forcipomyia taiwana, and Cra c 8 of the shrimp C. crangon) also consist of allergens essentially in dust mites and insects (
3.3. Other proteins
Other proteins involved in metabolic pathways (HSP70, thioredoxin) or displaying structural (tubulin) or physiological (hemocyanin and hexamerin) functions also occur as minor allergens in edible insects (Table 2). The hemolymph proteins hemocyanin and hexamerin both consist of homotetrameric proteins of high molecular mass, which share very conserved amino acid sequences and three-dimensional conformations. Hexamerin is widely distributed among insects and crustaceans, and it has been identified as an allergen of the fly maggot . The hemolymph protein hemocyanin has been identified as an allergen of the German cockroach (Bla g 3) and American cockroach (Per a 3) and of the giant freshwater prawn M. rosenbergii as well (
Owing to the conserved character, all the IgE-binding cross-reacting allergens of edible insects share very similar and readily superposable three-dimensional conformations. These structural similarities are illustrated in Figure 2, which shows the nice superposition of α-amylase, arginine kinase, glutathione S-transferase, trypsin, and hexamerin models of different origins. In fact, as shown for most of the members in different groups of evolutionary-related proteins, the three-dimensional conformations are much more conserved than the corresponding amino acid sequences.
4. Resistance of the insect allergens to proteolysis by digestive enzymes
Resistance to proteolysis consists of a property of paramount importance for food allergens, allowing them to escape the proteolytic degradation along the digestive tract and, thus, preserving their ability to stimulate the peripheral lymph nodes, e.g., Peyer’s patches, associated with the intestinal tract. In this respect, all of the putative insect allergenic enzymes such as α-amylase, arginine kinase, glutathione S-transferase, and trypsin exhibit a number of predicted cleavage sites by pepsin and trypsin distributed along their polypeptide chain and, especially, exposed on their molecular surface (Figure 3). Accordingly, the multiple proteolysis of all of these enzymes by pepsin, trypsin, and chymotrypsin generate a number of amino acids and short peptides apparently devoid of efficient IgE-binding properties (Figure 3). However, a limited number of peptides would keep a sufficient size (>10 amino acid residues), to properly stimulate the digestive immune system. In this respect, the allergenicity of tropomyosin, myosin, α-amylase, and hexamerin from the yellow mealworm (T. molitor), the giant mealworm beetle (Zophobas atratus), and the litter beetle (Alphitobius diaperinus) was reduced but not abolished following both in vitro simulated gastric fluid (SGF) and in vitro simulated intestinal fluid (SIF) digestion and heat treatment [17, 29]. The heat resistance of the major allergens of edible insects implies that both cooked insects and insect protein-containing food products retain some intact allergenicity. Heat and proteolysis stability of tropomyosin from the mud crab (Scylla serrata)  and the tropical oyster Crassostrea belcheri  have been similarly pointed out.
5. What extent for the allergy to edible insects?
To date, only a few cases of allergenic manifestations caused by the consumption of edible insects have been reported in the literature. The first case reports deal with occupational allergies of particularly exposed environmental searchers, fishers, and food industry workers [21, 28, 31–37]. Similarly, the well-known “pancake syndrome” (oral mite anaphylaxis), caused by the unintended consumption of mite-contaminated foods, has been identified in Refs. [38, 39]. Interestingly, most or less severe cases of anaphylaxis caused by the ingestion of various edible insects, reported in Chinese journals [40–51], were collated by Ji et al. , who counted up to 358 episodes of anaphylactic shock caused by food ingestion from 1980 to 2007. The most common offending allergens were identified as pineapple (25%), the soft-shelled turtle (Trionychidae) (19%), crabs (9%), and edible insects (locust + grasshopper) (14%). Other cases of anaphylaxis caused by the ingestion of edible insects were subsequently reported, mainly in Asia [53–55]. More recently, a majority of shrimp-allergic people (13 over 15) were confirmed as being allergic to yellow mealworm (T. molitor) when tested in double-blind, placebo-controlled food challenge (DBPCFC) . In this respect, yellow mealworm appears as a food at least as allergenic as shrimps to trigger anaphylactic responses in shrimp-allergic patients.
The limited number of reported cases of anaphylaxis due to edible insect consumption seems to be largely underestimated, especially in countries like China, where a great variety of insects are traditionally consumed as a source of dietary proteins. The occurrence in all of the edible insects of IgE-binding allergens which cross-react with the major allergens tropomyosin and arginine kinase of shrimps, dust mites, mollusks, and even nematodes suggests that shrimp-allergic and mollusk-allergic patients are at risk when consuming edible insects or insect-containing food products. However, further large-scale investigations among a broad population of shrimp- and mollusk-allergic patients will be necessary to appreciate the real allergenic risk edible insects pose to previously sensitized individuals. In the meantime, it would be wise to inform the consumers for such a potential risk, e.g., by a proper labeling of insect foods and insect-containing food products.
Obviously, the repertoire of food allergens from edible insects consists of a number of IgE-binding cross-reactive allergens common to other arthropods, e.g., dust mites and crustaceans, mollusks, and, more scarcely, nematodes. These pan-allergens refer to muscle proteins, enzymes, and proteins with structural and physiological functions. However, the search of identities the insect proteins share with known allergens of the allergen bank as a criterion for identifying allergens of edible insects suffers from some limitations associated to the completeness and quality of the bank. Most of the allergenic proteins of animal or plant origin essentially belong to abundant and widespread protein families in both animal and plant species like tropomyosins, lipocalins, and caseins for animals and cupins, profilins, and prolamins for plants . Moreover, depending on the data bank used for searching the identities with known allergens, the accuracy and exhaustiveness of the results might vary considerably. In this respect, the continuously updated FARRP AllergenOnline bank offers a maximum of guarantee for the retrieved information . Accordingly, all of the allergens identified to date correspond to proteins already known for their allergenic properties. Other allergens more specific of insects remain to be identified and characterized, in order to have a more accurate idea about the variability and specificity of the edible insect allergens. A serological approach using IgE-containing sera from allergic patients will be necessary to fulfill such a requirement, instead of the computational approach reported in this chapter. As insect food could be so allergenic that it can trigger strong anaphylactic responses in allergic persons, it is recommended that all insect food and insect-containing food products should mention this allergy possibility very clearly in the product labels.