Par j 2
Summary
Par j 2 is a major allergen of the wall pellitory (Parietaria judaica) weed pollen. Par j 2 belongs to the nonspecific lipid transfer protein (nsLTP) family. Relevant cross-reactivity to Par j 2 is limited to Par j 1 and pollen homologues from other Parietaria species. Of note, Par j 2 does not cross-react with nsLTPs from other allergenic sources, including Pru p 3 from peach and Art v 3 from mugwort pollen. Therefore, Par j 2 sensitization is a marker of genuine sensitization to pollen from Parietaria.
Epidemiology
Worldwide distribution
The wall pellitory (P. judaica), a weed of the Urticaceae family, growing in Mediterranean and temperate areas, such as Central and Eastern Europe, parts of the United Kingdom, the United States, and Australia, is a frequent cause of pollen sensitization and allergy in the Mediterranean area and the Iberian Peninsula [1-3].
Par j 2 is a major P. judaica pollen allergen, binding IgE from 80% - 83% of patients allergic to P. judaica [1, 4, 5].
Among Italian subjects with a suspicion of airborne or food allergy, the prevalence of Par j 2 sensitization was 25.71%, ranking 6th among 75 allergenic molecules, and peaking around 35% in people aged 46-55 years [6]. At the low end, in Central Europe, the prevalence of Par j 2 IgE is low, reported at 0.9% in a population of pollen-sensitized patients with doctor-diagnosed allergy in the Czech Republic [7].
Monosensitization to Par j 2 was observed in less than 2% of Italian subjects [6].
Clinical Relevance
Detailed information regarding P. judaica pollen allergy is available in the whole allergen section. P. judaica pollinosis is often associated with severe respiratory symptoms, such as asthma and/or severe allergic rhinitis [3, 9].
Disease severity and prediction
Detection of Par j 2 IgE confirms genuine sensitization to P. judaica, which is often associated with moderate/severe AR, and symptoms or diagnosis of asthma [9, 10]. Conversely, Par j 2 sensitization was detected in only 7% of weed allergic patients living in areas with low exposure to P. judaica pollen, pointing to genuine sensitization to other weed species than P. judaica [5]. In Italian patients, a cut-off level of 6.52 kuA/L for Par j 2 IgE has been proposed for discriminating P. judaica allergic patients from sensitized subjects, with a positive predictive value (PPV) of 94.7% and a negative predictive value (NPV) of 100% [11].
Regarding plant food allergy, Par j 2 is not involved in its pathophysiology or diagnosis [12, 13]. In fact, in patients with plant food allergy, detectable Par j 2 sensitization has even been associated with a lower prevalence of food-induced severe, systemic symptoms (odds ratio 0.64, p = 0.025) [10]
Cross-reactive molecules
Par j 2 shares partial cross-reactivity with the nsLTP Par j 1, another major allergen of P. judaica [3], but not with other nsLTP [1, 10]. Thus, it may be considered as unrelated to food nsLTPs from a clinical viewpoint [13].
Diagnostics
Marker allergen for genuine sensitization to P. judaica pollen
Par j 2 is a marker of genuine sensitization to P. judaica pollen, with excellent PPV and NPV [1, 2]. The association of Par j 1 and Par j 2 for the diagnosis of P. judaica pollinosis has been suggested [3]. As Par j 2 does not cross-react with nsLTPs other than Par j 1, such as Pru p 3 or Ara h 9, Par j 2 must not be used as a marker of food nsLTP syndrome [12].
As Par j 2 does not cross-react with nsLTPs other than Par j 1, such as Pru p 3 or Ara h 9, Par j 2 must not be used as a marker of food nsLTP syndrome [12].
Recombinant Par j 2 suitable for P. judaica diagnosis can be obtained using bacterial, yeast, and insect expression vectors [3].
Cross-Reactivity
Par j 2 lacks cross-reactivity with other nsLTPs outside Par j 1 [1]. Moreover, no pattern of associated sensitization was observed in a large-scale study in Italian subjects [6], although some authors reported Par j 2 and Pru p 3 sensitization levels may display a low level of correlation of uncertain clinical relevance [17, 18].
AIT Prescription
Detectable Par j 2 IgE confirms genuine sensitization to P. judaica, hence assisting with AIT selection [1, 2]. Ongoing research shows that a combination of Par j 1 and Par j 2, or engineered hypoallergenic hybrids of Par j 1 and Par j 2, are promising approaches for future AIT in P. judaica allergic patients [3, 19].
Exposure
The main route of exposure is through inhalation of P. judaica pollen.
Prevention And Therapy
Experimental trials
Not relevant.
References
- Matricardi, P.M., et al., EAACI Molecular Allergology User's Guide. Pediatr Allergy Immunol, 2016. 27 Suppl 23: p. 1-250.
- Gonzalez-Rioja, R., et al., Diagnosis of Parietaria judaica pollen allergy using natural and recombinant Par j 1 and Par j 2 allergens. Clin Exp Allergy, 2007. 37(2): p. 243-50.
- Dorofeeva, Y., et al., Expression and characterization of recombinant Par j 1 and Par j 2 resembling the allergenic epitopes of Parietaria judaica pollen. Sci Rep, 2019. 9(1): p. 15043.
- Duro, G., et al., cDNA cloning, sequence analysis and allergological characterization of Par j 2.0101, a new major allergen of the Parietaria judaica pollen. FEBS Lett, 1996. 399(3): p. 295-8.
- Stumvoll, S., et al., Identification of cross-reactive and genuine Parietaria judaica pollen allergens. J Allergy Clin Immunol, 2003. 111(5): p. 974-9.
- Scala, E., et al., Cross-sectional survey on immunoglobulin E reactivity in 23,077 subjects using an allergenic molecule-based microarray detection system. Clin Exp Allergy, 2010. 40(6): p. 911-21.
- Panzner, P., et al., A comprehensive analysis of middle-European molecular sensitization profiles to pollen allergens. Int Arch Allergy Immunol, 2014. 164(1): p. 74-82.
- De Linares, C., et al., Parietaria major allergens vs pollen in the air we breathe. Environ Res, 2019. 176: p. 108514.
- Sala-Cunill, A., et al., Prevalence of asthma and severity of allergic rhinitis comparing 2 perennial allergens: house dust mites and Parietaria judaica pollen. J Investig Allergol Clin Immunol, 2013. 23(3): p. 145-51.
- Scala, E., et al., Lipid transfer protein sensitization: reactivity profiles and clinical risk assessment in an Italian cohort. Allergy, 2015. 70(8): p. 933-43.
- Comite, P., et al., Par j 2 IgE measurement for distinguishing between sensitization and allergy. Allergol Int, 2015. 64(4): p. 384-5.
- Skypala, I.J., et al., The diagnosis and management of allergic reactions in patients sensitized to non-specific lipid transfer proteins. Allergy, 2021. 76(8): p. 2433-2446.
- Asero, R., et al., The clinical relevance of lipid transfer protein. Clin Exp Allergy, 2018. 48(1): p. 6-12.
- Longo, V., et al., Multiple IgE recognition on the major allergen of the Parietaria pollen Par j 2. Mol Immunol, 2015. 63(2): p. 412-9.
- IUIS/WHO. IUIS/WHO Parietaria judaica. 2021 December 29 2021]; Available from: http://allergen.org/search.php?allergenname=&allergensource=Parietaria+judaica&TaxSource=&TaxOrder=&foodallerg=all&bioname=.
- Gonzalez-Klein, Z., et al., The key to the allergenicity of lipid transfer protein (LTP) ligands: A structural characterization. Biochim Biophys Acta Mol Cell Biol Lipids, 2021. 1866(7): p. 158928.
- Faber, M.A., et al., IgE-reactivity profiles to nonspecific lipid transfer proteins in a northwestern European country. J Allergy Clin Immunol, 2017. 139(2): p. 679-682 e5.
- Skypala, I.J., et al., Lipid Transfer Protein allergy in the United Kingdom: Characterization and comparison with a matched Italian cohort. Allergy, 2019. 74(7): p. 1340-1351.
- Bonura, A., et al., Modulating allergic response by engineering the major Parietaria allergens. J Allergy Clin Immunol, 2018. 141(3): p. 1142-1144 e3.