Food Allergens

Atypical IgE-Mediated Conditions

Non-IgE-Mediated Conditions

Characteristics and

Reaction Mechanisms

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Types of Allergenic Proteins

• Storage proteins, especially in nuts, seeds and cereal grains

• Inhibitors of enzymes that may be destructive to storage factors, for example:– Inhibitors of alpha amylases that might break

down starches– Anti-trypsin protects against trypsin breakdown

of proteins in cereal grains

• Structural proteins

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Types of Allergenic Proteins

• Regulatory proteins, such as profilins, that are important in plant fertilization (for example in pollens)

• Pathogenesis-related proteins: proteins involved in the defense-related activities of the plant, for example:– Hevamines that are lysozyme-like enzymes that break

down fungal cell walls and defend the plant against fungal attack

• Lipid transfer proteins (LTP) that are essential in the functioning of a cell

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Allergenic Proteins in Specific Foods

• Each food contains many proteins, some of which are potential allergens, and have different characteristics and degree of allergenicity: for example:

• MILK– Contains about 30 potential allergens, some of which are

heat stable; some are heat labile:• Caseins (α; β; κ) tend to be heat stable• Whey proteins including alpha-lactalbumin and beta-

lactoglobulin tend to be heat labile

– Individuals allergic to only heat labile proteins usually can drink heated milk with impunity

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Allergenic Proteins in Specific Foods: Wheat

• Protein makes up ~12% of the dry wheat kernel • Many of the proteins in wheat are allergenic• Wheat proteins are roughly divided into the following

four classes• Gliadins• Glutenins• Albumins• Globulins• Gliadins contain as many as 40 to 60 distinct components• Glutenins contain at least 15• Albumins and Globulins also may be allergenic• Allergy to specific proteins tends to be population-

related

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Egg Allergens• Eggs contain many different proteins that can lead to

allergy• An egg-allergic individual is likely to be sensitized to

more than one protein• Although egg yolk contains several proteins, egg white

(ovalbumin) contains the greatest number of allergens• Up to 24 different antigenic protein fractions have been

isolated, although the allergenicity of most of them is unknown

• The main allergens are:– Ovalbumin– Ovomucoid– Ovotransferrin – Lysozyme

Peanut Allergens

The major allergenic peanut proteins have been characterized and named. The “Ara h” in the name of each protein is derived from the Latin name for peanut, Arachis hypogaea:

• Ara h 7

• Ara h 8

• Ara h agglutinin

• Ara h LTP

• Ara h oleosin

• Ara h TI

• Ara h 1• Ara h 2 (5 subtypes)• Ara h 3• Ara h 4• Ara h 5• Ara h 6

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Relative importance of individual peanut allergens in allergy

• Ara h 2 recognized most frequently as the causative allergen in all tests for symptom-triggering allergens and induced a reaction at relatively low concentrations

• Ara h 1 and Ara h 3 were recognized less frequently and reacted only at 100-fold higher concentrations than Ara h 2

• Presence of Ara h 2 suggested as marker for peanut allergy

Koppelman et al 2004 8

Prevalence of sensitization to all peanut allergens• Population of 40 patients sensitized to peanut:• Ara h 1 (65%)• Ara h 2 (85%)• Ara h 4 (53%)• Ara h 5 (13%)• Ara h 6 (38%)• Ara h 7 (43%)• Although Ara h 6 was considered a minor allergen, the

authors found that sensitization to Ara h 6 was associated with more severe clinical symptoms than most of the other allergens

Becker et al 2001 9

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Chemical Structure of Food Allergens

• Allergenic proteins from an increasing number of foods have been characterised

• The Food Allergy Research Resource Program (Farrp) database (http://www.allergenonline.com) contains details of unique proteins of known sequence that are classified as food allergens

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Classification of Food Allergens [Sampson 1999]:

Class 1 food allergens:• Encounter the immune system through the

digestive tract• Induce allergic sensitization directly via the

intestine• Are resistant to digestive enzymes• Are stable in response to gastric acid• Are heat-stable and are not deactivated by

cooking

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Class 2 food allergens

• Do not induce allergic sensitization in the digestive tract

• Rapidly dissolve in the oral cavity

• Are readily broken down by digestive enzymes

• Are susceptible to acid in gastric secretions

• Are heat-labile and are generally deactivated by cooking.

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Class 1 Food Allergens Characteristics

• Physicochemical properties that confer allergenicity are relatively unknown

• Usual characteristics of allergenic fraction of food:– Protein or glycoprotein– Molecular size 10 to 70 kDa– Heat stable– Water soluble– Relatively resistant to acid hydrolysis– Relatively resistant to proteases (especially

digestive enzymes)

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Incidence of Allergy to Specific Foods

• In young children: 90% of reactions caused by:– Milk - Soy

– Egg - Wheat

– Peanut

• In adults: 85% of reactions caused by:– Peanut - Tree nuts

– Fish

– Shellfish

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Incidence of Allergy to Specific Foods

• Increasing incidence of allergy to “exotic foods” such as:

– Kiwi

– Papaya

– Seeds: Sesame; Rape; Poppy

– Grains: Psyllium

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Major Allergenic Foods:Annex IIIa EU Directive on Labeling of Foods

Which Must be Declared

• Cereals containing gluten, (i.e. wheat, rye, barley, oats, spelt, kamut or their hybridized strains) and products thereof

• Crustaceans and products thereof

• Eggs and products thereof

• Fish and products thereof

• Peanuts and products thereof

• Soybeans and products thereof

• Milk and products thereof (including lactose)

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Major Allergenic Foods:Annex IIIa EU Directive on Labeling of Foods

Which Must be Declared Continued

• Nuts i.e. almonds, hazelnuts, walnuts, cashews, pecan nuts, Brazil nuts, pistachio nuts, macadamia nuts and Queensland nuts and products thereof

• Celery and products thereof • Mustard and products thereof • Sesame seeds and products thereof • Sulphur dioxide and sulphites at concentrations of

more than 10 mg/kg or 10 mg/litre expressed as SO2.

• Lupin and products thereof • Molluscs and products thereof

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Panallergens• Most allergenic foods contain species-specific

proteins• This means that individual sensitisation to a food

is specific to that food and none other, even if the foods are zoologically or botanically related

• However, recent research is indicating that some proteins with the same function in different food plants or animals may be allergenic

• May be:– Lipid transfer proteins

– Pathogenesis-related proteins

– Profilins

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Panallergens continued

• A person sensitised to such a protein may then be sensitive to the same protein where it occurs in different species

• The proteins tend to be weakly allergenic• Such allergens have been designated

“Panallergens”• Examples include:

– Parvalbumins in fish– Proteins responsible for oral allergy syndrome

and latex allergy

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Oral Allergy Syndrome(OAS)

OAS refers to clinical symptoms in the mucosa of the mouth and throat that:

• Result from direct contact with a food allergen• In an individual who also exhibits allergy to

inhaled allergens• Usually pollens (pollinosis) are the primary

allergens• Pollens usually trigger rhinitis or asthma in these

subjects

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Oral Allergy SyndromeCharacteristics

• Inhaled pollen allergens sensitise tissues of the upper respiratory tract

• Tissues of the respiratory tract are adjacent to oral tissues, and the mucosa is continuous

• Sensitisation of one leads to sensitisation of the other• First described in 1942 in patients allergic to birch

pollens who experience oral symptoms when eating apple and hazelnut

• OAS symptoms are mild in contrast to primary food allergens and occur only in oral tissues

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Oral Allergy SyndromeAllergens

• Pollens and foods that cause OAS are usually botanically unrelated

• Several types of plant proteins with specific functions have been identified as being responsible for OAS:– Profilins– Pathogenesis-related proteins

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Oral Allergy SyndromeAllergens

• Profilins are associated with reproductive functions

• Pathogenesis-related proteins tend to be expressed when the tree is under stress (e.g. growing in a polluted area; exposed to potential pathogens)– May be hevamines

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Oral Allergy SyndromeCross-Reactivity

• Occurs most frequently in persons allergic to birch and alder pollens

• Also occurs with allergy to:– Ragweed pollen– Mugwort pollen– Grass pollens

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Oral Allergy SyndromeAssociated foods

• Foods most frequently associated with OAS are mainly fruits, a few vegetables, and nuts

• The foods cause symptoms in the oral cavity and local tissues immediately on contact:– Swelling

– Throat tightening

– Tingling

– Itching

– “Blistering”

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Oral Allergy SyndromeCharacteristics of Associated foods

• The associated foods usually cause a reaction when they are eaten raw

• Foods tend to lose their reactivity when cooked• This suggests that the allergens responsible are

heat labile• Allergic persons can usually eat cooked fruits,

vegetables, nuts, but must avoid them in the raw state

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Oral Allergy Syndrome (OAS):Cross-reacting Foods and Pollens

Pollen Allergen

Birch

Mugwort

Grass

Timothy Grass

Fruit

Apple

Apricot

Cherry

Kiwi fruit

Melon

Nectarine

Orange

Peach

Pear

Plum

Prune

Watermelon

Vegetables Herbs and Spices

Anise

Asparagus

Cabbage

Carrot

Celery

Coriander

Cumin

Dill

Fennel

Green peppers

Parsley

Parsnip

Potato

Tomato

Legumes and Grains

Beans

Lentils

Peanuts

Peas

Soy

Rye

Nuts and Seeds

Almond

Chestnut

Hazelnut

Walnut

Caraway seed

Poppy seed

Sesame seed

Sunflower seed

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Oral Allergy SyndromeCross-reacting allergens

• Ragweed pollen with:– Banana– Cantaloupe– Honeydew– Watermelon– Other Melons– Courgette– Cucumber

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Oral Allergy Syndrome Diagnosis

• Syndrome seen most often in persons with birch pollen allergy compared to those with allergy to other pollens

• Seen in adults much more frequently than children• Reactions to raw fruits and vegetables are the most frequent

food allergies with onset in persons over the age of 10 years• Has also been described in persons with IgE-mediated

allergy to shrimp and egg This may not be true OAS; allergy may be

expressed as symptoms in the mouth in conditions distinct from OAS

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Expression of OAS Symptoms

• Oral reactivity to the food significantly decreases when food is cooked

• Reactivity of the antigen depends on ripeness– Antigen becomes more potent as the plant material ages

• People differ in the foods which trigger OAS, even when they are allergic to the cross-reacting pollens– Foods express the same antigen as the allergenic pollen, but

not all people will develop OAS to all foods expressing that antigen

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Identification of Foods Responsible for OAS Symptoms

• Skin tests will identify the allergenic plant pollen• Skin testing has not been successful in identifying

persons who react to cross-reacting food antigens– Plant antigens are unstable and do not survive the process

of antigen preparation– Crushing plant material leads to release of phenols and

degradative enzymes

• Prick + prick technique are more reliable than standard skin tests– Lancet is inserted in raw fruit or vegetable, withdrawn

and then used to prick the person’s skin

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Latex Allergy

• Allergy to latex frequently starts as a Type IV (contact) hypersensitivity reaction

• Contact is with an allergenic protein usually through:– Abraded (non-intact) skin– Mucous membrane by inhalation– Exposed tissue (e.g. during surgery)

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Latex AllergyCross-reacting allergens

• As antigen comes into contact with immune cells, repeated exposure seems to lead to IgE mediated allergy

• Reaction becomes systemic• Similar proteins in foods tend to trigger the

same IgE response• In extreme cases can cause anaphylactic

reaction

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Category Food

Type IIIClinical findingsIdentification of cross-reactive allergens

Avocado ChestnutBanana PistachioBell pepper WalnutCassavaCeleryCherimoyaChestnutCustard appleKiwi fruitMangoPapayaPassion fruitPotatoTomato

Type IIClinical findings Characterization of cross-reactive components by extract inhibition assays

Fig TurnipMelon Zucchini PeachPineapple

Type IClinical findings only

AppleApricotAubergine (eggplant)CarrotCherryCoconutLoquatSpinachStrawberryWatermelon

Foods with Allergens Similar to Latex

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Common allergens in unrelated plant materials: Summary

• OAS and latex allergy are examples of conditions in which common antigens, expressed in botanically unrelated plants, are capable of eliciting a hypersensitivity reaction

• Previous assumptions that plant foods in the same botanic family are likely to elicit the production of the same antigen- specific IgE are thus questionable

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Common allergens in unrelated plant materials: Summary

• In practice, when a specific plant food elicits an allergic response, foods in the same botanic family rarely elicit allergy

• It is important to recognize the allergenic potential of antigens common to certain botanically unrelated plant species, and take appropriate measures to avoid exposure of the allergic individual to them

Non-IgE-Mediated Allergies

Eosinophilic Gastrointestinal Diseases Food Protein Induced Enteropathies

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Eosinophilic Gastrointestinal Diseases (EGID)

• Expanded definition of food allergy now encompasses any immunological response to food components that results in symptoms when the food is consumed

• Example is group of conditions in the digestive tract in which infiltration of eosinophils is diagnostic

• Collectively these diseases are becoming known as eosinophilic gastrointestinal diseases (EGID).

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Characteristics of EGID

• Inflammatory mediators are released from the eosinophils, and act on local tissues in the oesophagus and gastrointestinal tract, causing inflammation

• In eosinophilic digestive diseases there is no evidence of IgE, therefore tests for IgE-mediated allergy are usually negative

• Unless there is a concomitant IgE-mediated reaction to food

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Characteristics of EGID

• Eosinophils are also found in abundance in the intestinal canal in diseases such as:– inflammatory bowel disease– infections caused by parasites such as

helminths and nematode worms

• These need to be ruled out before EGID is diagnosed

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Eosinophilic Oesophagitis• Symptoms most frequently associated with EO

and considered to be typical of the disease include:– Vomiting

– Regurgitation of food

– Difficulty in swallowing: foods are said to be sticking on the way down

– Choking on food

– Heartburn and chest pain

– Water brash (regurgitation of a watery fluid not containing food material)

– Poor eating

– Failure to thrive (poor or no weight gain, or weight loss)

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Eosinophilic Oesophagitis• Although the symptoms resemble gastro-

oesophageal reflux disease (GORD), the reflux of EO dose not respond to the medications used to suppress the gastric acid and control regurgitation (antireflux therapy) in GORD

• There is emerging data to suggest that use of acid-suppressing medications may predispose patients to the development of EO

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Diagnosis of EO

Three criteria must be met:

• Clinical symptoms of oesophageal dysfunction

• Oesophageal biopsy with an eosinophil count of at least 15 eosinophils per high-power (x400 mag) microscopy field

• Exclusion of other possible causes of the condition

Dellon ES 2013

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Eosinophilic Oesophagitis

Foods most frequently implicated

in Children

• Egg • Cow’s milk• Soy• Wheat• Corn• Peanuts

• Tree nuts• Shellfish• Fish• Beef• Rye

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Six-Food Elimination Diet and EoEAdult study 2013

• Foods eliminated:– Cereals

• Wheat• Rice• Corn

– Milk and milk products– Eggs– Fish and seafood– Legumes including peanuts– Soy

Lucendo et al 2013

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Six-Food Elimination Diet and EoE

• Indicators of positive outcome:– Biopsy eosinophil count (< 15/hpf)– Negative gastro-oesophageal reflux

• Reduced eosinophil count: 73.1% of subjects• Maintained remission for 3 years• Incidence of single triggering factors:

– Cow’s milk 61.9%– Wheat 28.6%– Eggs 26.2%– Legumes 23.8%

• No correlation with allergy tests

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Eosinophilic Gastroenteritis:

Diagnosis by biopsy:Abnormal number of eosinophils in the stomach and small intestine

Foods most frequently implicated

• Egg• Cow’s milk• Soy• Wheat

• Peanuts• Tree nuts• Shellfish• Fish

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Eosinophilic Proctocolitis

Diagnosis by biopsy:Abnormal number of Eosinophils confined to the colon

Foods most frequently implicated

• Cow’s milk

• Soy proteins

Most frequently develops within the first 60 days of life

Is a non-IgE-mediated condition

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Food Protein Enteropathies• Increasing recognition of a group of non-IgE-

mediated food-related gastrointestinal problems associated with delayed or chronic reactions

• Conditions include:– Food protein induced enterocolitis syndrome

(FPIES)– Food protein induced proctocolitis (FPIP)

• These digestive disorders tend to:– Appear in the first months of life– Be generally self-limiting– Typically resolve at about two years of age

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Food Protein Induced Enterocolitis Syndrome:Symptoms

Symptoms in infants typically include:• Profuse vomiting• Diarrhoea, which can progress to dehydration and

shock in severe cases• Increased intestinal permeability• Malabsorption• Dysmotility• Abdominal pain• Failure to thrive (typically weight gain less than 10

g/day)• In severe episodes the child may be hypothermic

(<36 degrees C)

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FPIES Characteristics• Triggered by foods, but not mediated by IgE• Condition typically develops in response to food

proteins as a result of digestive tract and immunological immaturity

• Cow’s milk and soy proteins, usually given in infant formulae, reported as most frequent causes

• Milk and soy-associated FPIES usually starts within the first year of life; most frequently within the first six or seven months

• When solids foods are introduced, other foods may cause the condition

• Recent research claims that rice is the most common food causing FPIES

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Cause of the Syndrome• Immune system reaction in FPIES appears

to involve T helper cells that release the cytokine TNF-α, which is typical of a Th1 response

• This is in contrast to allergy, in which a Th2 response releases the cytokines that result in the production of IgE

• Abnormally low level of TGF-, which is the cytokine most frequently involved in the development of tolerance to foods, suggests lack of immunological tolerance

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Foods Associated with FPIES

Removal of the culprit foods usually leads to immediate recovery from the symptoms

Foods that have been identified as triggers of FPIES in individual cases include:

• Milk• Cereals (oats, barley and rice)• Legumes (peas, peanuts, soy, lentils)• Vegetables (sweet potato, squash)• Poultry (chicken, turkey)• Egg

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Prevention of FPIES

• Most reports of FPIES indicate that exclusive breast-feeding is protective in potential cases of FPIES

• None of the infants who later developed FPIES after the introduction of solids had symptoms while being exclusively breast-fed

• Authors of these studies suggest that babies with FPIES while being breast-fed were sensitized to the proteins through an infant formula given during a period of immunological susceptibility

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Diagnosis and Management of FPIES

• There are no diagnostic tests for FPIES at present

• Indicators include clinical presentation :– development of acute symptoms

immediately after consumption of the offending foods (often milk- or soy-based infant formula)

– absence of positive tests for food allergy • Elimination and challenge with the suspect

foods will usually confirm the syndrome

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Diagnosis and Management of FPIES

• Removal of the offending food leads to symptom resolution

• In most cases delayed introduction of solid foods is advised because of the possibility that until the child’s immune system has matured, a similar reaction to proteins in other foods may elicit the same response

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Food Protein Induced Proctitis/Proctocolitis

• Blood in the stool is typical• Condition typically appears in the first few months

of life, on average at the age of two months• The absence of other symptoms, such as vomiting,

diarrhoea, and lack of weight gain (failure to thrive) usually rules out other causes such as food allergy, and food protein enteropathies

• Usually the blood loss is very slight, and anaemia as a consequence of loss of blood is rare

• Diagnosis is usually made after other conditions that could account for the blood, such as anal fissure and infection, have been ruled out

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Food Triggers of FPIP

• Most common triggers of FPIP include:– Cow’s milk proteins– Soy proteins– Occasionally egg

• Many babies develop the symptoms during breast-feeding in response to milk and soy in the mother’s diet

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Causes and Management of FPIP

• The cause of FPIP is unknown, but does not involve IgE, so all tests for allergy are usually negative

• In most cases, avoidance of the offending food leads to a resolution of the problem

• When the baby is breast-fed, elimination of milk and soy from the mother’s diet is usually enough to resolve the infant’s symptoms

• Occasionally egg can cause the symptoms, in which case, mother must avoid all sources of egg in her diet as well

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Progression of FPIP

• In most cases, the disorder will resolve by the age of 1 or 2 years

• After this age, the offending foods may be reintroduced gradually, with careful monitoring for the reappearance of blood in the baby’s stool

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ProbioticsMicroorganisms in the Bowel

• The healthy large bowel sustains a resident microbiota of bacteria, fungi, and other harmless microorganisms

• Beneficial effects include:– Synthesis of vitamins:

• Vitamin K• Biotin• Thiamin• Folic acid• Vitamin B12

– Interaction with immune cells to maintain a healthy epithelium

– Positive competition with invading pathogens to resist disease

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Bowel Microflora and Allergy• The type of gut colonization during the first weeks of life may

predispose an individual to atopic disease• Microflora of the bowel of a breastfed infant is different from

that of a formula-fed baby

• The gut microflora influences:– Resistance to infection– Immunological environment for subsequent challenges,

including food allergens– May influence predominance of Th1 or Th2 response

• Research studies suggest that lactobacilli and bifidobacteria may stimulate a Th1 (protective) response in the digestive tract without causing disease.

_________________Kirjavainen et al 1999

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Clinical Trials of Probiotics

• Not all probiotics have been tested in clinical studies with regard to allergy prevention or treatment

• L. bulgaricus seemed to have no effect on immune parameters, whereas it was associated with lower frequency of allergies

• L. acidophilus consumption accelerated recovery from food allergy symptoms

• These effects have also been observed in infants with eczema and cow's milk allergy using infant formulas supplemented with L. rhamnosus.

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Trials on Probiotics and Eczema Prevention

• Pregnant women took capsules containing Lactobacillus rhamnosus GG (LGG) during the last two to four weeks of pregnancy

• The newborn infants were given the same microorganism from birth to six months by spoon

• Breast-feeding mothers continued to take the capsules during lactation

• Subjects taking the probiotic had a reduced risk of developing atopic dermatitis (eczema) compared to controls up to 4 years of age

• Other studies found no reduced incidence of eczema in babies treated with probiotics

______________________Kalliomaki et al 2003Kalliomaki et al 2003

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Probiotics and Lactose Intolerance

• Lactobacilli, bifidobacteria and Streptococcus thermophilus assist in reducing the symptoms of lactose intolerance

• Produce the enzyme beta-galactosidase (lactase) in yogurt

• Microbial lactase breaks down lactose• The fermented milk itself delays gastrointestinal

transit, thus allowing a longer period of time in which both the human and microbial lactase enzyme can act on the milk lactose.

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Microflora and Lactose Intolerance

• Lactose tolerance in people who are deficient in lactase may be improved by continued ingestion of small quantities of milk

• Does not improve or affect the production of lactase in the brush border cells of the small intestine

• Continued presence of lactose in the colon contributes to the establishment and multiplication of bacteria capable of synthesizing the beta-galactosidase enzyme over time

• Resident micro-organisms will break down the undigested lactose in the colon

• Reduces the osmotic imbalance within the colon that is the cause of much of the distress of lactose intolerance ______________________

de Vrese et al 2001de Vrese et al 2001

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Status of Probiotics as Therapy

• Great care must be taken in transferring data from laboratory and experimental animal studies into human use

• Applies also to the use of known probiotics, some of which are already present in human nutrition, such as yoghurt

• Not all strains of bacteria in use as probiotics are completely harmless

• Their immune-modifying effects and possible antiallergic and anti-cancer actions require large clinical studies

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Potential Allergens in Probiotics

Although probiotics are generally considered to be safe, there are hazards for the allergic individual:– All yoghurts and other fermented milk

probiotic preparations must be avoided by milk-allergic individuals

– Many probiotic strains, especially Lactobacillus are grown on media containing milk proteins, especially casein. These may be incorporated into non-milk probiotic products

Potential Allergens in Probiotics

– Saccharomyces boulardii is used in some formulations. Persons allergic to brewer’s and baker’s yeast (Saccharomyces cerevisiae) may be allergic• There is debate as to whether

Saccharomyces boulardii is a subspecies of Saccharomyces cerevisiae or a separate entity. Traditional techniques cannot distinguish between the two

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