Significance of carbohydrate epitopes in a latex allergen with beta-1,3-glucanase activity

One of the latex allergens, Hev b 2, has beta-1,3-glucanase activity. The entire sequence of this allergen is already known. There is one potential N-glycosylation site in this molecule ((27)Asn). Heterogeneous glycosylation of this Asn residue could be a source of the multiplicity of natural Hev b 2. Possible participation of the carbohydrate epitopes of latex beta-1,3-glucanase isoenzymes in their IgE-binding capacity and cross-reactivity was investigated in this study.

beta-1,3-Glucanase isoenzymes were separated based on their affinities for concanavalin A. IgE-binding capacity and cross-reactivity were examined by immunoblotting and enzyme-linked immunosorbent assay (ELISA). Sequence heterogeneity among the isoenzymes was probed by peptide mass mapping after lysyl endopeptidase digestion. To clarify the relation to Hev b 2, N-terminal sequencing was performed on a fragmented peptide common to the separated isoenzymes.

Basic beta-1,3-glucanase was subdivided into two glycosylated isoenzymes (GI and GII) and one non-glycosylated isoenzyme (GIII). IgE antibodies in latex-positive sera chiefly recognized the glycosylated isoenzymes. Inhibition ELISA supported the significance of the carbohydrate epitopes for the IgE recognition and cross-reactivity. However, non-glycosylated GIII, as well as GI and GII, produced positive results in a skin prick test. The three beta-1,3-glucanase isoenzymes shared a partial sequence in common with Hev b 2.

Our results suggest that the carbohydrate epitopes in Hev b 2 homologues are relevant to an in vitro diagnosis of latex allergy and the accompanying cross-reactivity. Carbohydrate epitopes do not necessarily provoke allergic symptoms. Therefore, the actual allergenicity of Hev b 2 and its homologues should be carefully evaluated not only by in vitro IgE tests but also by in vivo tests.