Plants containing Allergens: Mode of action and classification

Plants containing allergens

What are allergens?

An allergen is any exogenous substance usually an antigen, which produces an abnormally vigorous immune response by triggering the production of specific Immunoglobin E IgE antibodies produced by activated B-lymphocytes cells. This activated immune response fights off a perceived threat that would otherwise be harmless to the body. Such immune reactions in response to the allergen are called as allergies.

Mode of action

Allergens are protein in nature and their activity depends upon their ability to interact with specific IgE antibodies. These IgE antibodies bind to the surface of the mast cells via IgE receptors, this occurs when first time an allergy prone person comes across an allergen.  Upon re-exposure the allergen binds the already bounded IgE and activates the mast cells releasing a variety of vasoactive mediators causing a hypersensitivity reaction and the symptoms of allergy.  Mast cells are the resident granulocytes that contain many granules rich in histamine and heparin. In some patients the early phase response is followed 4-8 hours later by persistent swelling and local inflammation. This is known as the late phase reaction and is mediated by basophils, eosinophils and macrophages.

Different types of allergy diseases are given below:

·         Urticaria (skin allergy)

·         Allergy to insect venom

·         Anaphylaxis  

·         Angioedema (skin allergy)

·         Atopic dermatitis (skin allergy or eczema)

·         Allergic conjunctivitis (eye allergy)

·         Allergic rhinitis (hay fever)

·         Allergic asthma

·         Food allergy

·         Drug allergy

·         Respiratory allergy (hay fever)

Classification of the plants allergens:

Most of the allergens are protein in nature so they can be easily be classified on the basis of their amino acid sequence and their three-dimensional structure. This classification consists of five families of allergens which are as follows:

1.      Prolamin superfamily

Most common allergen containing plants belong to this family. This family consists of 57 food allergens and 51 isoallergens. Examples are soy cereals and nuts like peanuts belong to this family.

2.      EF hand domain

This domain includes allergens present in cods and carps including 26 food allergens and 26 isoallergens. These allergen proteins are involved in calcium binding.

3.      Cupin super family

Most allergens in this super family are legumes, nuts and seeds. Members of this family belong to seed storage globulins. It includes 24 food allergens and 26 isoallergens.

4.      Profilin

Most of the allergens are 12-15k Da proteins usually found in eukaryotes. 24 food allergens and 20 isoallergens are present in this group. Pollen allergy is usually associated with this group.

5.      Bet v1- related proteins

Allergens widely distributed among vascular plants especially the families like Rosaceae, Apiaceae, and Fabaceae. 18 food allergens and 88 isoallergens are present.

Few plants which contain allergens are given below: