Studies on the stability of diluted allergen extracts using the radioallergosorbent test (RAST)

Abstract

Summary Allergen extracts from birch pollen, timothy pollen and horse dandruff were investigated. The influence of storage time, volume of extract in the vial and various additives on the potency of diluted extracts was tested with the radioallergosorbent test (RAST). The potency of diluted pollen extracts was found to decrease more rapidly than the potency of diluted dandruff extracts. The differences in allergen activity seen in RAST between freshly diluted extracts and stored extract dilutions were roughly reproducible in skin tests and histamine release tests from passively sensitized chopped human lung. The higher allergen stability of the dandruff extracts could, at least in part, be explained by the higher protein content of these extracts. An adsorption of allergen to the glass wall was shown to be the most probable cause to the more rapid decrease of allergen activity seen in pollen extracts stored in vials only partly filled. With addition of 0.2% Tween 20 after storage the potency of the extracts became almost equivalent to that of corresponding dilutions stored in filled vials.

Standardization of Allergens

“…Skin test titrations (4, 61) preferably with a histamine reference (3, 4), immunodiffusion (10,37), histamine release assays (10,23,24,49), RAST inhibition ( 5 , 9, 23, 30), isoelectric focusing (68), crossed immunoelectrophoresis (CIE) (50,70), lectin binding (16) and passive cutaneous anaphylaxis (7) have all been used to standardize allergen extracts. Use of combinations of some of the above methods, in particular skin tests, histamine release, RAST inhibition and CIE, has proved to be the most satisfactory approach to allergen standardization using the existing technology.…”

Clinical Studies of a Purified Timothy Pollen Extract

“…We tried to repeat tests every year under similar conditions, taking the risk of possible errors due to extract decay into consideration. Extract decay is more rapid when the extracts are diluted [10]. Prelimi nary results from recent studies on purified preparations indicate that extract decay is very rapid when the protein contents are re duced below 10 /ig/ml [8], i.e.…”

“…The relation between different allergen ic components may also vary from one al lergen batch to another. Moreover, allergen extracts do not remain stable during stor age, especially in diluted solutions [10]. On the other hand, the use in desensitization therapy of highly purified preparations, for example antigen E, the major allergen of ragweed pollen, has not yielded better re sults than crude ragweed extracts [17],…”

Allergen Assay and Extract Potency Estimation

“…A RAST-based method designed as a direct titration has been described by Ceska et al [1972] and Foucard et al [1972Foucard et al [ , 1973. As used in our laboratory [Yman ct al., 1974] the procedure can be utilized for potency estimations and the potency expressed in arbitrary units calculated from the amount of extract required to ob tain 50% of the maximal response.…”