This cytokine is sufficient to induce low affinity IgE, which however does not induce severe allergic symptoms, while additional cytokines from Tfh13 cells, including IL-13 and IL-21, are required for the development of high affinity IgE and anaphylaxis, a severe and potentially lethal condition.4 High affinity IgE-mediated mast cell activation is the major mechanism for the induction of severe type-1 allergic reactions. The gene discussed is IGHE; the disease is anaphylaxis.