IMMUNOLOGICAL AND MOLECULAR CHARACTERIZATION OF AMB P V ALLERGENS FROM AMBROSIA-PSILOSTACHYA (WESTERN RAGWEED) POLLEN

We have purified and characterized the Amb p V allergen (A1 variant) f rom western ragweed (Ambrosia psilostachya) pollen. This allergen was found to be highly cross-reactive with the Amb a VA1 allergen From sho rt ragweed (A. artemisiifolia) pollen in a competitive double-Ab radio immunoassay (DARIA) and the two allergens showed concordant allergenic potency in histamine-release experiments. We cloned and sequenced sev eral Amb p V genes from western ragweed pollen and flowers by direct P CR of genomic DNA. The amino acid sequences deduced from the nucleotid e sequences indicated the presence of multiple forms of Amb p V that c ould be broadly classified into two groups: Amb p VA and Amb p VB vari ants. The sequences of the Amb p VA variants are highly homologous to Amb a V (about 90% identity) and very similar to the protein sequence that we obtained. The Amb p VB variants share approximately 65% amino acid homology with Amb a V and have five to seven cysteine residues as compared with the eight found in Amb a V and Amb t V. Two cysteine re sidues that form disulfide bonds in other Amb Vs (positions 19 and 43 in Amb a V) are replaced by serine and alanine in the Amb p VB1 and Am b p VB2 variants. We have generated model structures of Amb p VA1, VA2 , VA3, and VB1 variants from the nuclear magnetic resonance-derived st ructure of Amb a VA1 by homology modeling. Comparison of antigenic epi topes predicted for the structures of Amb p V variants and Amb a VA1 e xplains the observed crossreactivity of the two ragweed proteins and s uggests the epitopes likely to be involved in Ab recognition.