The expanding role(s) of eosinophils in health and disease

Abstract

Surprisingly, the role(s) of eosinophils in health and disease is often summarized by clinicians and basic research scientists as a pervasive consensus opinion first learned in medical/graduate school. Eosinophils are rare white blood cells whose activities are primarily destructive and are only relevant in parasitic infections and asthma. However, is this consensus correct? This review argues that the wealth of available studies investigating the role(s) of eosinophils in both health and disease demonstrates that the activities of these granulocytes are far more expansive and complex than previously appreciated. In turn, this greater understanding has led to the realization that eosinophils have significant contributory roles in a wide range of diseases. Furthermore, published studies even implicate eosinophil-mediated activities in otherwise healthy persons. We suggest that the collective reports in the literature showing a role for eosinophils in an everincreasing number of novel settings highlight the true complexity and importance of this granulocyte. Indeed, discussions of eosinophils are no longer simple and more often than not now begin with the question/statement "Did you know . . .?" (Blood. 2012;120(19):3882-3890)

Eosinophil Peroxidase Catalyzed Protein Carbamylation Participates in Asthma

“…The recruitment and activation of eosinophils in the airways is a characteristic feature of asthma, and the role of eosinophils in the pathogenesis of this disorder has long been a focus of intense investigation. Classically, eosinophils are recognized for their oxidative and antimicrobial activities, but more recently, eosinophils have been recognized for directly regulating T cell function and immune responses, contributing to allergic respiratory inflammation (57). Accordingly, an improved understanding of the basic chemical pathways available to eosinophils for generating specific reactive oxidants and diffusible radical species in vivo, and for eliciting changes in inflammatory signaling is of interest.…”

Effect of Long-Term Green Tea Extract Supplementation on Peripheral Blood Leukocytes in CrossFit-Trained and Untrained Men

“…Considering the fact that EGCG decreases VCAM-1 expression, it might be speculated that post-supplementation increase in eosinophil count was associated with changes in interaction and enhanced eosinophil recruitment from the marginal to the circulating pool. Jacobsen et al (2012) demonstrated that eosinophils were important regulators of local immunity and remodeling/repair (see below) and might play a role in maintaining metabolic homeostasis. Remodeling and repair are associated with physical training-related changes in cell structure and function; the processes may also be induced by thermogenic supplements enhancing adipose tissue metabolism (Mraz, Haluzik, 2014;Sadowska--Krępa, Pokora, Podgórski, Obara, Domaszewski, 2015;Pokora, Sadowska-Krępa, Żak, Domaszewski, 2016).…”

“…Our findings showed that 6-week GTE supplementation resulted in a significant increase in the absolute eosinophil count as well as eosinophil percentage in both study groups. An increase in eosinophil count in healthy individuals may be induced by non-allergic mechanisms (Jacobsen, Helmers, Lee, Lee, 2012) and a variety of agents (including EGCG) that interrupt eosinophil adhesion to the vascular endothelium (Blanchard, Rottenberg, 2008). Considering the fact that EGCG decreases VCAM-1 expression, it might be speculated that post-supplementation increase in eosinophil count was associated with changes in interaction and enhanced eosinophil recruitment from the marginal to the circulating pool.…”

Eosinophil activation markers in clonal and non-clonal eosinophilia

“…In solid tumors, eosinophils do not belong to the intrinsic malignant process and eosinophilia is induced by eosinophilopoietic and tumor cells-secreted cytokines (25). Previous studies showed that eosinophils are cytotoxic against tumor cells (3) and may be implicated in remodeling of the host connective tissue and blood vessels as a reaction to the growing tumor (3,26). We investigated 5 patients with solid tumors (2 with colon cancer, 1 with lung cancer, 2 with uterine cancer).…”

“…This view has become more nuanced and now eosinophils are considered multifunctional leukocytes, true immunoregulatory cells with roles which imply: increase fibrosis, vascular leakage, angiogenesis, epithelial desquamation, epithelial metaplasia and smooth muscle hypertrophy (3). Recent studies suggest that instead of destructive endstage effector cells, eosinophils play an important role in regulating local immunity and in remodeling/repairing processes, either in normal conditions (plasma cells survival, thymic development and T-cell selection, metabolic homeostasis, female reproductive system, mammary gland development, reproductive homeostasis) and also in pathological conditions (cancer and tumor biology, transplant rejection, demyelinating diseases, pulmonary hypertension, acute lung injury, eosinophilic esophagitis, inflammatory bowel disease, allergic/chemical contact dermatitis) (3). Eosinophils represent approximately 1-5% (<500cells/µl) of all blood leukocytes.…”