Characterization of the allergen group VI in timothy grass pollen (Phl p 6). I. Immunological and biochemical studies.

For the identification and characterization of allergen grass group VI we performed two-dimensional immunoblotting of timothy grass pollen (Phleum pratense). Two intense 13-kD protein spots of pI 5.2 and 5.5 were found to be IgE reactive. By N-terminal microsequencing and amino acid analysis we identified them as Phl p 6 isoallergens. An antiserum was raised against Phl p 6 by immunizing BALB/c mice with allergen bearing nitrocellulose particles of one isoform. The antiserum revealed an intense reactivity to Phl p 6 isoforms, but also showed a weak cross-reactivity with Phl p 5 allergens. After immunoabsorption of patients' serum to Phl p 6 spots on the blotting membrane, we were able to demonstrate that the eluted human IgE antibodies cross-react with the grass group V allergens as well. Therefore, Phl p 5 and Phl p 6 possess one or more common IgE binding epitopes.