Repeated inhalation of allergen leads to the down-regulation of allergen-sp
ecific IgE responses in non-atopic individuals as well as in mice. This phe
nomenon is named inhalation-induced IgE tolerance. In contrast, inhaled all
ergen causes significant IgE and allergic responses in atopic persons. The
mechanisms involved in this differential regulation of airway allergen-spec
ific immune responses remain unclear. Besides the allergen exposure of gene
tically susceptible individuals, environmental contamination is considered
to play a role as an initiating factor for airway allergic responses. Using
a murine model, we demonstrate here that airborne beta-1,3-D-glucan, which
exists frequently in our environment, particularly in highly humid areas,
can abrogate inhalation-induced IgE isotype-specific downregulation and pro
mote airway eosinophil infiltration to inhaled antigen.