Inhalation of most proteins does not cause IgE-mediated responses, whereas a limited number of small protein allergens can elicit such reactions. Although the mechanism of allergic induction is not completely clear, some general principles have emerged. Allergens presented transmucosally at very low doses induce IgE responses by TH2 cells. This subset of cells produces the primary cytokines, interleukin-4 (IL-4) and interleukin-13 (IL-13). These interleukins interact with receptors on B lymphocyte cell surfaces, which promote class switching to the IgE antibody subclass. The subsequent class switch produces antigen-specific IgE antibodies with specifity toward common allergens such as pollen, animal dander, food, or venom.