Cross‑reactivity between Parietaria judaica and Parietaria officinalis in immunotherapy extracts for the treatment of allergy to Parietaria

Parietaria judaica and P. officinalis are the two most common subspecies of the Parietaria genus. P. judaica and P. officinalis have exhibited cross-reactivity in previous studies. P. judaica pollen is the main cause of allergy in the Mediterranean area. It has been shown that a high percentage of patients sensitized to P. judaica with allergic rhinitis (AR) have an increased risk of developing asthma. The present study aimed to confirm the cross-reactivity between P. judaica and P. officinalis and to evaluate the use of a single P. officinalis extract in patients allergic to both subspecies as a preferable option for the diagnosis and treatment of allergy in a highly pollinated area of the Spanish Mediterranean coast. The present study was a single centre, observational cross-sectional study of adult patients diagnosed with AR and/or bronchial asthma who were sensitized to Parietaria pollen. A total of 24 patients were enrolled in the study and included in the analysis. Allergovit® immunotherapy extracts were selected for the study based on the protein content (P. officinalis pollen extract). The results of an in vitro ELISA revealed that 79.1% (n=19) of the patient sera were reactive to immunotherapy extracts. ELISA inhibition assay of the IgE binding to P. officinalis demonstrated inhibition values >70% in the sera of highly reactive patients, confirming the cross-reactivity between the two Parietaria subspecies. In addition, all patients enrolled in the study exhibited double skin positivity against P. judaica and P. officinalis extracts, as assessed by the skin prick test, further supporting the in vivo reactivity between the two subspecies. The present study demonstrated that P. judaica and P. officinalis pollen extracts were highly cross-reactive, and that a unique P. officinalis pollen extract may be used for the diagnosis and immunotherapy of patients allergic to Parietaria.