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. 2019 May 15;20(10):2397.
doi: 10.3390/ijms20102397.

Cashew Tree Pollen: An Unknown Source of IgE-Reactive Molecules

Daniele Danella Figo  1 , Karine De Amicis  2 , Denise Neiva Santos de Aquino  3 , Fabiane Pomiecinski  4 , Gabriele Gadermaier  5 , Peter Briza  6 , Clovis Eduardo Santos Galvão  7 , Jônatas Bussador do Amaral  8 , Carlo de Oliveira Martins  9 , Fabio Fernandes Morato Castro  10   11 , Jorge Kalil  12   13   14 , Keity Souza Santos  15   16   17
Affiliations

Cashew Tree Pollen: An Unknown Source of IgE-Reactive Molecules

Daniele Danella Figo et al. Int J Mol Sci. .

Abstract

Pollinosis is sub-diagnosed and rarely studied in tropical countries. Cashew tree pollen has been reported as an allergen source although the knowledge of its immunoglobulin E (IgE)-reactive molecules is lacking. Therefore, this work aimed to identify IgE-reactive molecules and provide a proteomic profile of this pollen. From the 830 proteins identified by shotgun analysis, 163 were annotated to gene ontology, and a list of 39 proteins filtered for high confidence was submitted to the Allfam database where nine were assigned to allergenic families. Thus, 12 patients from the northeast of Brazil with persistent allergic rhinitis and aggravation of symptoms during cashew flowering season were selected. Using a 2D-based approach, we identified 20 IgE-reactive proteins, four already recognized as allergens, including a homolog of the birch isoflavone-reductase (Bet v 6). IgE-reactivity against the extract in native form was confirmed for five patients in ELISA, with three being positive for Bet v 6. Herein, we present a group of patients with rhinitis exposed to cashew tree pollen with the first description of IgE-binding proteins and a proteomic profile of the whole pollen. Cashew tree pollen is considered an important trigger of rhinitis symptoms in clinical practice in the northeast of Brazil, and the elucidation of its allergenic molecules can improve the diagnostics and treatment for allergic patients.

Keywords: Brazil; aeroallergens; novel allergens; pollinosis; proteome; shotgun analysis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Cashew flowers and pollen particles. (a) a cashew flower, (b) autofluorescent image of anthers from a cashew flower (scale bar represents 100 µm), (c) autofluorescent image of pollen grains from a cashew flower (scale bar represents 20 µm), (d) pollen grain from a cashew flower used for measurement (scale bar represents 100 µm).
Figure 2
Figure 2
Proteomics of cashew tree pollen reveals the presence of allergenic protein families and IgE-reactive molecules. (a) Summarized workflow and results of the proteomic analyses. (b) 2D-SDS-PAGE (isoelectric point (pI) 3–10 and 4–7) stained by Coomassie. All excised spots subjected to mass analysis are numbered (1–27 and 28–56). (c) Gene ontology annotation of identified proteins from cashew tree pollen using PantherDB. A total of 163 proteins were annotated to a biological process, cellular component, and molecular function.
Figure 3
Figure 3
Immunoblot analysis of cashew tree pollen extract. (a) Pollen extract (E) on reducing SDS-PAGE and stained with Coomassie. Immunoblot of individual allergic patients’ sera (n = 12), negative controls (NC1, NC2, and NC3) and second antibody control (2nd). (b) 2D Western blotting (2D WB) showing the IgE binding of pooled sera (1–12) to cashew tree pollen extract. (c) Phylogenetic tree built from species found in homolog proteins identified after 2D WB. Species close to Anacardium occidentale are highlighted in bold. pI, isoelectric point.
Figure 4
Figure 4
Cashew tree pollen and recombinant birch isoflavone-reductase (Bet v 6) are recognized by patients’ sera in ELISA. (a) IgE reactivity to immobilized cashew tree pollen extract was assessed with individual patients’ sera (n = 12) and non-atopic human sera (n = 5). (b) IgE reactivity to immobilized recombinant Bet v 6 was assessed with patients’ sera that were positive in ELISA for cashew tree pollen extract (n = 5) and non-atopic human sera (n = 5). The NS indicates the response threshold calculated as 3× SD of the buffer control signal.
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