Abstract: An inhibition assay for measuring the potency of allergen extracts by incubating a mixture of allergen extract and reference allergen specific IgE in a buffered solution with an insoluble support to which reference allergen is adhered. The conjugated IgE adhering to the insoluble support is reacted with an enzyme labeled anti-IgE antibody and the enzyme label is contacted with a solution of a substrate which will yield a fluorescent product in the presence of the enzyme. The level of fluoresence in the solution is measured. The percentage of inhibition of the allergen specific IgE is determined from fluorescence levels measured for various extract concentrations.

Abstract: A chymopapain derivative having the enzymatic activity reduced by at least 95% while retaining the original allergenic activity of at least 90% is suitable for skin testing to detect allergic hypersensitivity to chymopapain and for treating patients exhibiting allergic hypersensitivity to chymopapain. The enzymatic activity can be blocked by reacting thiol groups of the enzyme with and iodoacetic acid, bromoacetic acid, or a salt, ester or amide derivative thereof, under conditions which block the undesirable enzymatic activity while retaining the desired allergenic activity.