Currently, ADHRs are categorized primarily based on Gell and Coombs’ classification system into type I reactions (also known as immediate-type allergic reactions) mediated by immunoglobulin E (IgE) antibodies, type II reactions (also known as cytotoxic allergic reactions) elicited by immunoglobulin G (IgG) or M (IgM) antibodies, type III reactions triggered by immune-complex deposition, and type IV reactions (also known as delayed-type reactions) induced by cellular immune mechanisms (16) (Figure 1). Here, IGHE is linked to allergic disease.