Functional characterization of complete and immunodominant epitopes of a novel pollen allergen from Parthenium hysterophorus.

Abstract

Summary: Background. Parthenium hysterophorus pollen induces chronic clinical conditions such as allergic rhinitis and bronchial asthma. Among the plethora of proteins in the pollens, only few were reported to induce allergy. Currently sensitization to P. hysterophorus pollen allergen is diagnosed by skin prick test (SPT) using the entire pollen extract instead of using the specific allergen. Methods. In P. hysterophorus sensitized patients, SPT was done using the crude pollen extract, 40 kDa allergenic pollen protein and two commercially synthesized allergen epitopes (17 and 24) of P. hysterophorus. Dot-blot of allergen epitopes was done using P. hysterophorus sensitized sera. Crude pollen extract (1, 1.25, 2.5, 5 and 10 µg/mL), 40 kDa allergenic protein (3 µg/mL), and allergen epitopes (3µg/mL) were used to perform Basophil Activation Test (BAT). Results. Crude pollen extract at 2.5, 5, 10 μg/mL and 40 kDa allergenic protein at 3μg/mL concentrations induced wheal and flare reaction by around 15 minutes, whereas commercially synthesized allergen epitopes at 3μg/mL induced wheal and flare reactions in less than 10 minutes. Allergen epitopes (3 µg/mL) revealed strong reactivity with sensitized patient's IgE in dot-blot analysis. Basophil activation Test using crude pollen extract (2.5, 5, 10 µg/mL), 40 kDa allergenic protein (3 µg/mL), and allergenic epitopes (3µg/mL) indicated significant basophil activation (as measured by CD63 expression) in sensitized patients. Conclusions. The 40 kDa allergenic protein and its allergenic epitopes (17 and 24) induced phenotypic and cellular immune responses in P. hysterophorus sensitized individuals. The tested allergenic epitopes (17 and 24) induced faster wheal and flare reactions in comparison with the crude extract and the 40 kDa allergenic protein. The novel 40kDa allergenic protein and its allergen epitopes identified here may be useful for the development of component-resolved diagnosis (CRD) while also serving as a potential therapeutic lead for desensitization treatment for P. hysterophorus pollen induced allergy.