Proteomic and transcriptomic analyses reveal new insights into allergens in Ligustrum lucidum pollen

Pollen aeroallergens cause up to 40 % of respiratory allergies and are challenging to control due to their widespread distribution in the environment. The pollen of Ligustrum lucidum (privet) is a significant source of inhalant allergens. However, despite its clinical relevance, the protein composition of L. lucidum pollen remains poorly characterized. Therefore, we employed an integrated proteomic and transcriptomic approach to explore its potential allergen composition, focusing on possible cross-reactivity with Olea europea (olive), a well-studied allergenic relative. Using LC-MS/MS-based proteomics and RNA-seq transcriptomics, we detected 13 of the 15 known olive-like allergens, demonstrating high cross-species conservation. Proteomic analysis identified nine homologous allergens, including Ole e 1, Ole e 2, Ole e 3, Ole e 5, Ole e 6, Ole e 9, Ole e 12, Ole e 13, and Ole e 14. Transcriptomic analysis revealed four additional putative allergens: Ole e 8, Ole e 10, Ole e 11, and Ole e 15. These proteins shared 74–95 % sequence identity with their olive counterparts and exhibited multiple isoforms. Our findings provide a set of L. lucidum pollen potential allergens and highlight the utility of multi-omics in allergen discovery. However, further clinical validation of these putative novel allergens is needed to assess their role in sensitization and cross-reactivity.

Significance

Privet (Ligustrum), a genus within the Oleaceae family, is biologically significant due to its role in triggering allergic respiratory diseases worldwide. As a close relative of olive (Olea europaea) and ash (Fraxinus), privet shares allergenic proteins that contribute to cross-reactivity among sensitized individuals. Climate change has been shown to extend their flowering period, increasing pollen exposure and exacerbating allergic symptoms. Ligustrum is widely used in urban landscaping due to its rapid growth, resistance to pollution, and adaptability to diverse soil conditions, which facilitates its global spread across North America, Europe, Asia, and South America. Notably, L. lucidum is a major sensitizing agent in Mexico City, where 37 % of allergic patients react to its pollen. The first identified allergen, Lig v 1, shares homology with Ole e 1 and Fra e 1. At the same time, Lig v 2 (profilin) mirrors Ole e 2, highlighting the molecular basis for cross-reactivity within the Oleaceae family. Recent proteomic studies have uncovered additional allergens, including enolase, β-1,3-glucanase, and ATP synthase subunits, further elucidating privet's allergenic potential. The absence of genomic data for L. lucidum has hindered research; however, advances in transcriptomic and proteomic approaches have enabled the identification of 13 of 15 known olive-like allergens in privet pollen, paving the way for improved diagnostics and targeted therapies. This underscores the need for further investigation into Ligustrum's allergenic components, particularly as climate change and urbanization amplify its public health impact, as well as, the potential for improved diagnosis and targeted therapies.