Carbohydrates expressed on Aspergillus fumigatus induce in vivo allergic Th2-type response

The mould Aspergillus fumigatus (Af) causes several forms of Th2-biased diseases such as Type I respiratory allergies. This mould contains abundant carbohydrates including glucan, chitin and galactomannan. However, little is known on whether these carbohydrates directly drive Th2 responses in vivo.

We sought to determine the relative role of carbohydrates expressed on crude extracts of Af in the induction of Th2-type antibody production and local eosinophila in mice.

Carbohydrates on native Af were destroyed by sodium metaperiodate under mild conditions. CBA/J mice were sensitized intranasally with native, periodate-treated or mock-treated Af. Histologic changes and production of Af-specific IgE, IgG1 and IgG2a, as well as serum total IgE were determined. Inhibition ELISA for Af-specific IgE was performed using periodate-treated Af as an inhibitor.

Mice sensitized with periodate-treated Af displayed significant decreases in both total and specific IgE levels in comparison to mice sensitized with native or mock-treated Af. Furthermore, sensitization and subsequent challenge with periodate-treated Af significantly reduced the degree of eosinophil recruitment into the nasal mucosa, compared to the controls. On the other hand, competitive inhibition showed that periodate-treated Af could inhibit binding between native Af and specific IgE in a similar manner to that of native and mock-treated Af.

These results suggest that carbohydrates on Af play a key role as internal adjuvants in inducing the allergic Th2-type response and are not the targets of the induced IgE response.