Allergen extracts: Composition, manufacture, and labeling
- Robert E Esch, PhD
Robert E Esch, PhD
- Adjunct Professor, School of Natural Sciences
- Lenoir-Rhyne University
Allergens in this topic review will be defined as molecules capable of eliciting immunoglobulin E (IgE)-mediated hypersensitivity reactions. Allergen extracts are used in a variety of diagnostic and therapeutic applications, including diagnostic skin testing, provocation testing, and in vitro tests, as well as allergen-specific immunotherapy (both oral and subcutaneous). In all applications, the active ingredient is theoretically the relevant allergens from that source, although the formulation may differ between applications.
The production and standardization of allergen extracts are discussed in this topic review. The choice of specific extracts for use in clinical practice and other issues related to the use of allergen extracts are reviewed in more detail separately. (See "SCIT: Preparation of allergen extracts for therapeutic use", section on 'Types of allergen extracts' and "SCIT: Standard schedules, administration techniques, and monitoring".)
COMPONENTS OF ALLERGEN EXTRACTS
Allergen extracts are complex mixtures of allergenic and nonallergenic substances including proteins, glycoproteins, polysaccharides, lipids, nucleic acids, low-molecular weight metabolites, salts, and pigments. Most allergens are proteins or glycoproteins, but in certain rare circumstances, pure carbohydrates or low-molecular weight chemicals can act as allergens. All foreign proteins are potential allergens in theory, although only a limited number of proteins are confirmed to be allergenic in humans. No structural properties have been identified that distinguish allergenic from nonallergenic proteins.
Allergen extracts are usually prepared by aqueous extraction of allergenic source materials obtained from natural sources. The composition and biologic properties may be influenced by the quality and purity of the source material, as well as their processing, extraction, and storage conditions. For batch-to-batch consistency, it is sufficient to consider the proteins as active ingredients.
Crude aqueous allergen extracts containing all of the extractable components of the source material can be used without further modification or subjected to further processing, including fractionation, physico-chemical modification, and combination with other allergen extracts . Most commercially available extracts are crude extracts.
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- COMPONENTS OF ALLERGEN EXTRACTS
- Major allergens
- The paradox of extract refinement
- SOURCE MATERIALS FOR ALLERGEN EXTRACTS
- Other materials
- - Fungi
- - Animals
- - Insects
- Accounting for natural variability
- MANUFACTURE OF ALLERGEN EXTRACTS
- Extraction and quality control of allergen extracts
- - Recombinant allergens
- Formulations of allergen extracts
- Modification of extracts
- - Chemical modification (allergoids)
- - Coupling with inorganic gels
- - Molecular modification
- - Special considerations for different routes of administration
- STANDARDIZATION OF ALLERGEN EXTRACTS
- UNITS OF MEASURE
- Units that do not reflect potency
- Units that reflect potency
- - Bioequivalent allergy unit
- - Biologic unit
- CHOOSING EXTRACTS FOR USE IN PRACTICE
- ALLERGEN EXTRACT PRODUCTION AROUND THE WORLD