Antigens and Allergens in Birch Pollen Extract

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Abstract
More than 70% of the total allergenic activity of a birch pollen (BP) extract was detected within die first 30 min of extraction. Fractionation of the BP extract by gel filtration and analysis of the eluted antigens by a fused rocket im‐munoelectrophoresis revealed at least three antigens with molecular weights of about 29 000, and 17 000–10 000, corresponding to antigens Nos. 2, and 7–8, respectively, in crossed‐immunoelectrophoresis (CIE) and in crossed‐radio‐immuno‐electrophoresis (CRIE). Gel isoelectrofocusing of the pooled allergenic fractions revealed two major protein bands with pl's around 5.6 and 5.7, probably corresponding to antigens Nos. 7–8 and No. 2, respectively. Antigens Nos. 7–8 were thennoresistant, while antigen No. 2 was thermolabile.The allergenic activity was determined by prick skin testing and by the RAST inhibition method. More than 90% of the allergenic activity in the fractions was located in the protein peak C (mol. wt. 10 000–17 000) containing antigens 7–8. About 30% of the total allergenic activity of the extract (1:10 w/v) was recovered in the peak C fractions, and only less than 0.5% outside these fractions. Higher allergenic activity was obtained for the peak B fractions (mol. wt. 29 000) by skin prick testing than by the RAST. Peak B contained allergens (antigen 2) distinct from those of peak C by the CRIE and by the RAST. The allergenic material in the low molecular weight fractions of peak D (mol. wt. 2000–5000) was allergenically similar to that of peak C in the RAST. Only weak and even negative skin reactions were observed with the peak D fractions in allergic subjects.