FCER2 and allergic disease: The clinical observations reviewed here provide only some clues as to the mechanisms by which the allergic disease may induce ISSNHL, ALHL, and MD (Figure 2), including increased serum total (ISSNHL, ALHL, and MD) and specific (ALHL and MD) IgE concentrations; increased numbers of circulating CD23+ cells (ISSNHL and MD); the ability of antigen challenge to provoke disease symptoms (MD); and finally, some efficacy of desensitization in reducing disease symptoms (MD).