RT Book, Section A1 Shomali, William A1 Gotlib, Jason A2 Kaushansky, Kenneth A2 Prchal, Josef T. A2 Burns, Linda J. A2 Lichtman, Marshall A. A2 Levi, Marcel A2 Linch, David C. SR Print(0) ID 1178748203 T1 Eosinophils and Their Disorders T2 Williams Hematology, 10e YR 2021 FD 2021 PB McGraw-Hill Education PP New York, NY SN 9781260464122 LK accessmedicine.mhmedical.com/content.aspx?aid=1178748203 RD 2024/03/29 AB SUMMARYEosinophils are specialized marrow-derived myeloid cells that play an important role in regulating the innate and adaptive arms of the immune system, in addition to tissue repair and remodeling. Eosinophil functions are mediated by their granular contents that include various proteins, enzymes, and inflammatory mediators. Under pathologic conditions, eosinophils can accumulate in any tissue, releasing their mediators and recruiting other cells, resulting in inflammation, thrombosis, fibrosis, and tissue damage. Eosinophilia is most commonly reactive (secondary) to other disorders such as infections, allergies, medications, autoimmune diseases, and malignancies. The categorization of primary (clonal) eosinophilias was revised in the 2008 World Health Organization classification of myeloid neoplasms and further modified in 2016, after the discovery of molecularly-defined subtypes, including “myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2” in addition to “chronic eosinophilic leukemia, not otherwise specified.” A diagnosis of idiopathic hypereosinophilia requires the exclusion of all primary and secondary causes as well as lymphocyte-variant hypereosinophilia, which is characterized by expansion of immunophenotypically-aberrant T cells that elaborate eosinophilopoietic cytokines. Several advances in the diagnosis and treatment of primary eosinophilic disorders have been achieved and are discussed in this chapter.