Comparative studies on tree pollen allergens. II. Isolation of alder (Alnus incana) pollen allergens: purification and some characteristics of the major allergen pI 4.78.

The aqueous extract of alder (Alnus incana) pollen was found to consist of a protein mixture amounting to 3% of the dry pollen weight. Separation by gel permeation chromatography on an AcA-54 column resulted in 6 fractions designated chronologically to their relative elution volumes (AI 1 to AI 6). The immunological reactivity of these fractions was demonstrated in both IgE and IgG test systems. Being both immunochemically and quantitatively dominant fraction AI 4 was selected for further purification by a semipreparative isoelectric focusing column. A well-resolved and apparently homogeneous component with a pI value of 4.78 was eluted from the IEF column. The homogeneity of this fraction was demonstrated by one sharp band in thin layer IEF, one single band in HVE, one distinct sharp peak in HPLC and a symmetrical precipitate in CIE. The molecular weight was estimated to 22,500 daltons. Fraction pI 4.78 was shown to be a major allergen of alder pollen, it elicited a 1.17 histamine wheal reaction in skin prick test at a concentration of 1 mg . ml-1 and showed a significantly high RAST inhibition in all of the reaginic sera used. Fraction pI 4.78 was found to be an adequate model allergen of alder pollen well suited for further immunochemical characterization.