IGHE and Alzheimer disease: Thus, while we will use the term HIES here to define a set of diseases characterized by very elevated IgE levels, elevated IgE levels can be seen in many patients with AD without an overt PAD due to many factors, including but not limited to the increased Th2 skew associated with AD and induction of IgE production by environmental factors such as S. aureus colonization (18, 56).