Problems raised by potency evaluation of allergen preparations

Wide variations are observed in the potency of allergen preparations available for use on humans. There are numerous methods of in vivo or in vitro testing: skin testing, passive anaphylaxis testing on animals, study of precipitins, histamine release tests on human leukocytes, radio-immunological assay test (RAST), blasticlymphocyte transformation test (TTB). The first investigations seemed to show that the allergenic potency of a large number of inducing substances was due to proteic activity; this gave rise to the theory that potency could be evaluated by protein nitrogen units (PNU). However, the protein content of an allergenic extract is not always active. In addition, natural specific proteins are altered during the extraction process or subsequently during preservation. Where the active antigen is known, comparison of different testing with various preparations may be made. The results show excellent correlation between the two biological results (cutaneous reaction and histamine release) and the content of E antigen. No relation with PNU has been observed. Certain authors propose the following: skin testing, PNU titration, dosage of certain elements (polysaccharides, lipids, phosphates, etc.), RAST. The great differences observed between the value of skin testing and the RAST may be due to the large number of active antigens in different 'dusts' and to the fact that the RAST method measures only IgE whereas allergic activity of these allergens is no doubt associated with other types of antibodies. The complexity of the problem shows that a great many studies are still necessary to provide a satisfactory solution.