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A 659 bp cDNA clone** coding for an allergen of Pj pollen has been isolated from a lambda gt 11 library, and its DNA sequence determined. The cDNA insert showed an open reading frame of 429 bp coding for an allergenic protein of 14,866 Da and a deduced amino acid sequence containing 143 residues. The expressed recombinant protein represented the major allergen Par j I since it reacted with 95% of the sera from Pj-allergic patients (n = 22) and with two Par j I-specific monoclonal antibodies. No similarity with other known DNA and protein sequences has been detected.

Parietaria is a genus of dicotyledonous weeds of the Urticaceae family including several species and its pollen grain is one of the most important allergenic sources in the Mediterranean area. Species belonging to this genus induce IgE responses in approximately 10 million people. Identification of allergens by means of independent strategies suggest that the allergens of the two more common species, Parietaria judaica and Parietaria officinalis, show molecular weights ranging between 10 and 14 kD and that the allergens of the two extracts are highly cross-reactive. Biochemical analysis and molecular cloning allowed the isolation and immunological characterization of the two major allergens of the P. judaica pollen, Par j 1 and Par j 2. Sequence comparison suggests that the P j major allergens of P. judaica belong to the nonspecific lipid transfer protein family, and three-dimensional modeling by homology has revealed that both proteins present a very conserved structural motif composed of four α-helices. Immunological analysis has shown that Par j 1 and Par j 2 are able to bind most of the P. judaica-specific IgE and some of their IgE determinants have been mapped. Recombinant Par j 1 and Par j 2 allergens have been shown to possess immunological properties equivalent to their natural counterpart and their availability represents a fundamental tool for the diagnosis and therapy of Parietaria pollen allergy.