Latin name: Parietaria judaica
Common names: Non-specific lipid transfer protein (ns-LTP), member of the pathogenesis-related 14 (PR-14) protein family.
Wall pellitory allergen components
Parietaria is a genus of dicotyledonous weeds of the Urticaceae family. Its pollen grains are among the most important allergenic triggers in the Mediterranean area and along the West coast of Europe as far north as central England. It is found in Australia and Argentina and two closely related species are found in the U.S. and one in Brazil. The genus Parietaria has about 10 species, which are highly crossreactive to each other (1). In some geographical areas a single species may dominate, and IgE antibodies to only one of the species can be found in sensitised individuals. Two species are commonly referred to as Wall pellitory: Parietaria judaica and Parietaria officinalis. Parietaria has a very long period of pollination, and often reaches peaks of more than 500 grains/m3 of air at the beginning of June (2).
The following allergens have been characterised so far.
- Par j 1, a lipid transfer protein (3).
- Par j 2, a lipid transfer protein (3).
- Par j 3, a profilin (4).
- Par j Calcium-binding protein (5).
Parietaria pollen allergens have been reported to be quite heterogeneous and to range from high- to low-molecular mass (6). Studies of allergens of the most common species, P. judaica and P. officinalis, have shown that the allergens of the extracts are highly cross-reactive. Allergenic components are most highly concentrated in the pollen; but they are present throughout the plant, including in the leaves and, in traces, in the stems (7).
Both Par j 1 and Par j 2 are major allergens of P. judaica and belong to the nonspecific lipid transfer protein family. Par j 1 and Par j 2 represent major allergenic components of Parietaria judaica pollen, since they are able to induce an immunoglobulin E (IgE) response in 80-95% of Pj-allergic patients (1,8-9).
Although P. judaica also contains a profilin allergen, less than 50% of patients sensitised to Birch and Grass profilin cross-react to Parietaria profilin; this is in contrast to a high prevalence of cross-reactivity of profilin from other pollens (4). Due to structurally similar pollen antigens in different Parietaria species, these are all equally useful in diagnosis, regardless of the pollen species to which the patient is sensitive or the prevalent species in the area (2).
Recombinant Par j 1 and Par j 2 allergens have been shown to possess immunological properties equivalent to those of their natural counterparts (1). As Par j 1 and Par j 2 have similar IgE epitopes, rPar j 2 may be a useful assessment tool for the diagnosis and therapy of Parietaria pollen allergy (3). (Despite their structural similarities, however, Par j 1 and Par j 2 are independent allergens, as demonstrated by cross-inhibition experiments showing that they possess an independent repertoire of IgE epitopes (9).
Recombinant allergens, which are genetically engineered isoforms resembling allergen molecules from known allergen extracts, have immunoglobulin E (IgE) antibody binding comparable to that of natural allergens and generally show good reactivity in in vitro and in vivo diagnostic tests (10). To date, many different recombinant allergens of pollens, molds, mites, bee venom, latex and foods have been cloned, sequenced, and expressed.
Recombinant allergens have a wide variety of uses, from the diagnosis and management of allergic patients to the development of immunotherapy to the standardisation of allergenic test products as tools in molecular allergology. Recombinant allergens are particularly useful for investigations in allergies manifesting wide cross-reactivity.
Allergens from Parietaria judaica listed by IUIS*
|Par j 1
||Par j 2
||Par j 3
|Par j 4
*International Union of Immunological Societies (www.allergen.org) Jan. 2008.
Recombinant non-glycosylated protein produced in an E. coli strain carrying a cloned cDNA encoding Parietaria judaica allergen Par j 2 (3,5)
Common names: Lipid transfer protein 2, LTP 2
Biological function: Nonspecific lipid transfer protein
Mw: 14 kDa
Other allergens isolated: rPar j 2.0101 (9)
rPar j 2 is a 14 kDa lipid transfer protein. Approximately 83% of Mediterranean weed-allergic patients, and 7% of non-Mediterranean weed-allergic patients, have been shown to be sensitised to this allergen (5). Lipid transfer proteins are represented in pollen, fruit and vegetables of a wide range of plant species.
rPar j 2 and the isoform rPar j 2.0101 are representative of Par j 2, a major allergen in P. judaica pollen. rPar j 2.0101 showed an allergenic activity and a capacity to bind IgE that are almost identical to those of the native allergens purified from aqueous pollen extract (11). Approximately 80% of individuals allergic to this pollen have been shown to be sensitised to these recombinant allergens (5,9). Furthermore, there is an amino acid sequence homology with rPar j 1.0101 of 45%, along with similar immunoglobulin E epitopes (3). The epitope of the major allergen Par j 1.0101 also present on Par j 2.0101, is an immuno-dominant epitope and is capable of inhibiting 30% of all specific IgE against the P. judaica major allergens (12).
A study evaluated the allergen profile of P. judaica IgE-reactive sera from 36 weed pollen-sensitised allergic individuals from the Mediterranean region with high Parietaria pollen exposure. They were compared with 69 weed pollen-allergic patients with little or no Parietaria exposure; 83% of the Mediterranean weed pollen-allergic patients mounted high IgE antibody levels (mean 20.89 kUA/L) against recombinant rPar j 2, whereas only 7% of the non-Mediterranean weed-allergic patients showed low level IgE reactivity to rPar j 2 (mean 1.03 kUA/L). The authors concluded that rPar j 2 might be used as a diagnostic marker allergen to identify weed pollen-allergic patients who are genuinely sensitised against Parietaria pollen and thus would be particularly suited for specific immunotherapy with Parietaria pollen extract (5).
In a study of sera of 29 P. judaica-allergic individuals tested against 5 recombinant peptides, at least 4 putative IgE-binding epitopes were identified. These results suggest that the recombinant rPar j 2 allergen contains IgE epitopes that are heterogeneously recognised by sensitive patients (13).
Lipid transfer proteins are panallergens that have a ubiquitous distribution in tissues of many plant species, resulting in variable degrees of cross-reactivity and particularly relevant cross-reactivity in fruits and vegetables (14-15).
Compiled by Dr Harris Steinman, email@example.com
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