Eosinophils and the Scope of Practice in Allergy/Immunology

The circadian nature of eosinophils and basal regulation now appears to be closely linked to the identification of type 2 innate lymphoid cells that constitutively express IL-5 and are induced to express IL-13, resulting in eotaxin production and eosinophil accumulation.6 Allen et al's review of the eosinophilic pneumonias highlights the often variable tissue responses involved with eosinophils.5 In 1989,9 the description of acute eosinophilic pneumonia (AEP), a syndrome of rapid-onset respiratory failure with a predominance of eosinophils in bronchoalveolar lavage fluid, was a critical sentinel article demonstrating the destructive nature of eosinophils in the lung. [...]when the clinician faces a patient for consultation of an elevated eosinophil count, a very practical case-based presentation brings the reader a well-organized, valuable algorithm for evaluating and treating these patients.14 The armamentarium of the allergy/immunology clinician includes glucocorticoids, imatinib, immunosuppressant medications, JAK inhibitors, tyrosine kinase inhibitors, and various biologic therapies depending on the target. Is long-term reduction or depletion of eosinophils safe? ◦What is the effect of removing eosinophils on homeostatic mechanisms in which eosinophils are believed to play a role, such as tissue remodeling, glucose metabolism, and tumor surveillance? ◦Will eosinophil depletion in patients with chronic eosinophilic disorders disrupt negative feedback loops, causing other cell types to proliferate, become more activated, or even undergo neoplastic transformation?