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IgE sensitization refers to the process where an individual's immune system produces IgE antibodies against a specific allergen, like dust mites or peanuts. This production of IgE antibodies does not mean the person will experience allergic symptoms upon exposure; it simply indicates that the immune system has become primed to react to that allergen. Doctors diagnose allergies through a combination of patient history, physical exams, allergy tests like skin prick or IgE blood tests, provocation test or food challenge. These tests help identify specific allergens triggering a patient's symptoms, which can then guide treatment. 
 

• IgE Antibodies:

Immunoglobulin E (IgE) is a type of antibody that plays a key role in allergic reactions. 
 

• Allergens:

Allergens are substances, often proteins, that trigger an immune response in susceptible individuals.
 

• Sensitization:

When a person is exposed to an allergen, their immune system may produce IgE antibodies specifically designed to target that allergen - a process known as sensitization. 
 

• Sensitization may not equal to Allergy:

While sensitization is a necessary step for an allergic reaction, it doesn't guarantee that symptoms will occur upon subsequent exposure. Some individuals may be sensitized without developing noticeable allergic symptoms. Therefore, clinicians will combine clinical symptoms to the blood test and/or skin test, and/or further diagnosis (e.g. provocation test/food challenge) in order to confirm if the patients are allergy or not.
 

• Allergic Disease:

Allergic disease develops when sensitized individuals experience allergic symptoms upon re-exposure to the allergen. The IgE antibodies bind to mast cells and basophils, triggering the release of chemicals that cause the symptoms. 

For example, someone can be sensitized to peanut and have IgE antibodies against peanut proteins, but not experience an allergic reaction when consuming peanut. However, repeated exposure to peanut or simultaneously exposure to other allergens may activate the IgE antibodies, triggering allergic symptoms such as hives, itching, or more severe reactions. 

• Cross-Reactivity:

Cross-reactive proteins are protein families that have similar structures. The immune system may produce IgE antibodies targeting multiple allergens under the same family. As a result, individuals may experience allergic symptoms when exposed to these allergens under the same protein family.

Common cross-reactivity protein families include:

PR-10 – Major allergen is Bet v 1 from birch pollen, cross-reacting pollens include hazel, alder, beech etc, cross-reacting food include raw fruits (e.g. apple, peach, kiwi), nuts (e.g. hazelnut, walnut) vegetables (e.g. carrot, celery, tomato), legumes (e.g. peanut, soybean). It may induce oropharyngeal symptoms and sometimes severe allergic reactions.

Profilins – Extremely common and involves virtually every plant source, patients may tolerate processed or cooked foods. Clinical reactions are usually mild. Cross-reacting pollens include birch, hazel, alder, oak, beech, cypress, date palm, ash, olive, mugwort, ragweed, wall pellitory,  timothy etc., plant foods include apple, peach, pear, melon, kiwi, pineapple, fig, celery, carrot, orange, peanut, soybean, tomato, hazelnut etc.

Non-specific lipid transfer proteins (nsLTP) – Clinical reactions can be systemic and severe, especially when not associated to birch pollinosis. Cross-reacting pollens include ragweed, mugwort, olive, plane etc., plant foods include apple, peach, cherry, grape, orange, tomato, lettuce, corn, wheat, hazelnut, walnut, peanut etc.
 

Polcalcins – There is extensive cross-reactivity among pollen polcalcins, e.g. ragweed, mugwort, birch, alder, Russian thistle, cypress, ash, olive, Bermuda grass, Timothy grass, pellitory. This can be considered as marker of polysensitization with unknown clinical relevance for respiratory symptoms.

Serum albumins – These allergens are present in dander, milk, serum, urine and meat of furry animals (cat, dog, horse, pig, cattle etc.), and are considered as minor allergens causing respiratory symptoms through inhalation. Serum albumin in food has been shown to elicit minor, moderate, and severe clinical symptoms upon ingestion. Pork–cat syndrome is a food allergy to pork in individuals sensitized to cats, caused by cross-reactivity between serum albumins in pork and cats. Similarly, bird–egg syndrome is an allergy to egg yolk and/or bird’s meat by ingestion and to bird dander by inhalation at the same time, due to cross-reactivity between serum albumins in birds and egg yolk.

Lipocalins – These are airborne allergens present in dander, saliva and urine of animals like horse, cat, dog, rabbit, mouse, rat, hamster. Sensitization to multiple animals’ lipocalins is associated with disease severity.

Tropomyosins – These are thermostable muscle proteins with a high allergenicity potential, which may result in low to severe clinical impact including anaphylaxis. There is high degree of immunological and clinical cross-reactivity between different species of shellfish (shrimp, crab, lobster, mussel, oyster etc), house dust mites (Dermatophagoides pteronyssinuss, Dermatophagoides farinae), storage mites (Blomia tropicalis), cockroaches and so. The shrimp (Penaeus monodon) major allergen, Pen m 1, is one of the most clinically relevant allergenic tropomyosins.

Arginine kinase – It is an enzyme found in various invertebrates, including insects (cockroach, house dust mites, storage mites, moths) and crustaceans (shrimp, crab, crayfish). It is heat-labile, which is sensitive to heat, acid, and alkaline conditions. Its allergenic potential tends to decrease upon thermal processing and digestion.

Parvalbumins – These are fish panallergens that are resistant to food processing, they can trigger allergy through ingestion, inhalation and contact. These allergens are found in herring, carp, cod fish, tuna, hake, swordfish, sole, salmon, trout, mackerel, catfish etc.