Latin name: Hevea brasiliensis
Common names: Prohevein (hevein precursor)
Hevea brasiliensis allergen Hev b 6.01
Class I endochitinase containing a hevein domain.
Hev b 6.01 (1-2), prohevein, is one of the most important Latex allergens in health care worker (HCW) Latex allergy. Prohevein, Hev b 6.01, is processed to yield 2 allergenic fragments, the N-terminal hevein, Heb b 6.02, and the C-terminal portion, Hev b 6.03 (3-4). All 3 allergens exist in the plant, although the ratio between Hev b 6.01 and Hev b 6.03 is about 30:1 (5). All 3 components act as independent allergens (2). Hevein comprises the most important part of IgE-binding epitopes in the prohevein molecule.
Hev b 6.01 was reported to be recognised by 88.9% of 54 Latex-allergic patients (6). Other studies have reported a prevalence of between 70-86% sensitisation to this allergen in Latex-allergic individuals (1, 7).
In a study of Latex-allergic patients, prohevein bound IgE from sera of 15 of 20 (75%) patients, and the prohevein C-domain bound 3 of 20 (15%) Latex-allergic patient sera. In ELISA, 36 of 52 (69%) patient sera showed IgE binding to prohevein, whereas 11 of 52 (21%) sera had IgE antibodies to the prohevein C-domain. Purified hevein inhibited 72% of IgE binding from pooled sera of Latex-allergic patients to solid phase glove extract and 45% of IgE binding to solid phase Natural rubber latex (NRL) (8).
The recombinant allergen has allergenic activity very similar to that of native Hev b 6.01. Seventeen of 18 (94%) serum samples from Latex-allergic HCW showed increased levels of allergen-specific IgE to rHev b 6.01, 16 (89%) to rHev b 6.02, and 13 (72%) to rHev b 6.03 in a study evaluating recombinant Hev b 6 allergens. In the Hev b 6.01 precursor, the regions responsible for IgE binding and those for inducing the T-cell proliferation responses are settled in different parts of the protein. The Hev b 6.02 domain is responsible for IgE binding and carries discontinuous B-cell epitopes, whereas Hev b 6.03 is a better inducer of a proliferation response and contains HLADR4- binding motifs (2).
Individuals with NRL allergy often have immediate reactions to plant-derived foods and fresh fruits, such as Avocado and Banana. More than 50% of subjects having IgE-mediated NRL allergy are reported to be sensitised to Avocado, as demonstrated by allergen-specific IgE. About 10-20% report hypersensitivity reactions after ingesting Avocado. The conserved hevein domain of the major Latex allergen prohevein (Hev b 6.01) is a ubiquitous chitin-binding protein structure that can be found in several plant proteins and may be responsible for the observed cross-reactivity between Latex and Avocado.
Sensitisation to endochitinase class I containing a hevein domain is the main underlying pathomechanism in Latex-mediated Avocado allergy (9). In a study evaluating skin testing against purified proteins in 15 patients with NRL allergy, 11 (73%) patients were found to have reactivity to isolated hevein-like domains of Avocado and Banana, but only 1 (7%) patient reacted to their corresponding endochitinases. Proteins from Avocado and Banana inhibited binding of IgE antibodies to prohevein (Hev b 6.01) in 59% and 38% of patients, respectively (10). Other studies have also identified this as the panallergen responsible (11). In immunoblotting studies, sera of 9 of 15 patients allergic to NRL with IgE antibodies to hevein also demonstrated specific IgE binding to 32- and 33-kDa Banana proteins (12). Similarly, in a patient who experienced an anaphylactic reaction to Apple juice containing acerola, cross-reactivity with Latex due to prohevein was demonstrated (13).