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Recurring reports of a highly allergenic 42-46-kDa protein in Hevea brasiliensis latex appeared to have been resolved with the discovery of a 43-kDa allergenic latex protein that was a homologue to patatin. However, the low to moderate prevalence of sensitization to the protein, designated Hev b 7, among latex-allergic patients could not adequately explain the frequent observations of the 42-46-kDa allergen. This led to the hypothesis that another, more allergenic protein of a similar molecular mass existed in Hevea latex. We report the isolation and purification of a 42.98-kDa latex glycoprotein showing homology to the early nodule-specific protein (ENSP) of the legumes Medicago sativa, Medicago truncatula, and Glycine max. The protein is allergenic, being recognized by immunoglobulin E (IgE) in sera from latex-allergic patients. The IgE epitope resides on the carbohydrate moiety of the protein, and the presence of a similar carbohydrate component on potato tuber patatin enables the latter to inhibit IgE binding to the ENSP homologue. The cDNA encoding the ENSP homologue was isolated by reverse transcription-PCR and cloned. The protein predicted from the cDNA sequence has 391 amino acids, the first 26 of which constitute a putative signal peptide. The deduced molecular mass of the mature protein is 40.40 kDa, while its isoelectric point is estimated at 5.0. The discrepancy between the predicted and observed molecular mass might be due to glycosylation, for which three N-sites on the protein are predicted. The purified protein showed lipase and esterase activities and may be involved in plant defense.

Sensitization to natural rubber latex has been linked to proteins from medical latex gloves. Various assays to estimate the amount of residual allergenic proteins extractable from latex gloves to assess their potential exposure hazard have inherent weaknesses.This investigation was aimed at developing 2-site immunoenzymetric assays and identifying appropriate protein markers to assess the allergenic potential of latex gloves.The presence of 6 latex allergens--Hev b 1, 2, 3, 5, 6, and 13--was measured in a cross-section of commercial latex medical gloves by using monoclonal and polyclonal antibody-based 2-site immunoenzymetric assays. The overall allergenic potential of these gloves was assessed by IgE-inhibition assay. Stepwise multiple regression analyses were performed to identify marker allergens that best explained the variation in latex glove allergenicity.All 6 latex allergens were detected in at least some of the glove samples. Hev b 5 and Hev b 13 were identified as the marker allergens that combined best to explain the variation in the glove allergenicity. The significant multiple correlation (R=0.855) between these 2 markers and glove allergenic potency forms the basis of an assay to gauge latex glove allergenicity.The overall allergenic potential of latex gloves can be estimated by using Hev b 5 and Hev b 13 as indicator allergens. The correlation between glove allergenicity and the level of these allergens was maintained for low-protein gloves (200 microg/g). This estimation of glove allergenicity was superior to that obtained by using total protein readings.

Rationale Identification of Hev b 7, a 43 kDa latex allergen homologue of patatin, did not adequately explain the frequent observations of IgE antibody reactivity to a 42–46 kDa protein in serum from latex-allergic patients. We thus hypothesized the existence of another allergenic Hevea protein of a similar molecular weight. We report on the isolation and purification of a 42.98 kDa latex glycoprotein showing homology to Early Nodule Specific Protein in legumes. Methods Hev b 13 was isolated from Hevea brasiliensis latex B-serum by gel filtration and ionic exchange chromatography. Binding of human IgE to Hev b 13 and inhibition of IgE binding by patatin were studied by Western immuno-blots analysis. The cDNA encoding Hev b 13 was isolated by RT-PCR and cloned. Results The protein predicted from the Hev b 13 cDNA sequence has 391 amino acids. The mature protein possessed a deduced molecular weight of 40.40 kDa and pI of 5.0. Prevalence of IgE antibody reactivity to native Hev b 13 was 78% (51/65) in latex-sensitized healthcare workers and 77% (10/13) in latex-sensitized spina bifida children. IgE-binding to Hev b 13 was inhibited by the potato tuber patatin but lost when the carbohydrate moiety of patatin was removed. This suggested that the IgE-specific epitope might reside on the glycan. Conclusions The lipolytic esterase, Hev b 13, is a major allergen of Hevea brasiliensis latex. The principal IgE-specific epitope of the glycoprotein appears to be located on its carbohydrate moiety.