Comparative studies on tree pollen allergens. IV. Evaluation of two commercially available allergen extracts of alder (Alnus incana) and birch (Betula verrucosa) pollen.

Two commercially available extracts of alder and birch pollen usually used in clinical allergy were evaluated and correlated to two corresponding reference extracts 'S' produced at the authors' laboratory. The set of extracts produced by ALK, Denmark are referred to as 'A', while those produced by Nyco, Norway are referred to as 'N'. The results of the CIE analysis demonstrated that, upon using the same antibodies, both the morphology and the intensity of the precipitates of the different extracts differed considerably. In the alder pollen extract, the 'N' preparation contained more immunoprecipitate lines than the two others. Extract 'S' contained the least number of antigenic lines. Only two of the antigenic lines bound specific IgE in CRIE and were represented in variable concentrations in the three extracts. These two allergenic precipitation lines were demonstrated to have an immunological reaction of identity as shown by tandem-CIE and tandem-CRIE systems, respectively. In the birch pollen system variable numbers of reproducible antigenic lines of precipitation were demonstrated. Preparation 'A' contained more antigens than the two other extracts. This extract lacked a cathodic antigen with slow electrophoretic mobility represented in 'N' and 'S'. One dominant antigenic line was commonly present in the three extracts and could bind IgE antibodies in the CRIE system. A minor cathodic allergen was shown by CRIE in extracts 'S' and 'N', but not in extract 'A'. The RAST and RAST-inhibition titration experiments in all extracts showed qualitative and quantitative similarities. The amino acid compositions and the carbohydrate analyses showed that extracts 'S' and 'N' were similar while extract 'A' contained higher concentrations of certain amino acids and carbohydrates. In both alder and birch pollen, the reference extract 'S' contained lower concentrations of the nonallergenic antigens and of the low molecular weight contaminants.