The emerging roles of eosinophils in mucosal homeostasis.

A study led by Drs. Shah K, Ignacio A, McCoy KD & Harris NL., published in Nat. Mucosal Immunol. 2020 Mar 10. Congratulations!

The emerging roles of eosinophils in mucosal homeostasis. Shah K., et al. PLoS Genet. Nat. Mucosal Immunol. 2020 Mar 10.

Fig. 1 Identification of tissue-resident eosinophils and their known homeostatic functions. Eosinophil development occurs in the bone marrow, arising from GATA-1+ granulocyte/macrophage progenitors (GMPs). Development into eosinophil-lineage-committed progenitors to (EoP) requires transcription factors c-EBPs and high expression of GATA1. During this transition between GMPs to EoPs, IL-33 can expand the pool of EoPs, upregulating expression of IL-5Ra. Development of EoPs into granule-mature eosinophils is facilitated by cytokines ILC2-derived IL-5 plus IL-3 and GM-CSF. Under homeostatic conditions, eosinophils exit the bone marrow into peripheral blood as mature cells identified as Siglec-F+ CCR3+ F4/80+ CD62L+ which have a relatively short half-life. Eosinophils are recruited into peripheral tissues in a manner dependent on local CCL11/eotaxin production. Tissue-resident eosinophils are primarily found in mucosal sites (i.e., GI-tract*, lung, mammary gland), but can also be found in the adipose and thymus where they are noted to contribute to various homeostatic and tissue-protective functions. The tissue microenvironment has significant influence on eosinophil characteristics demonstrated by discrepancies in surface marker expression and turnover rates.

Abstract

Eosinophils are granulocytes, typically implicated as end-stage effector cells in type-II immune responses. They are capable of producing a wide array of pre-formed molecules which render them with vast potential to influence a wide variety of processes. Nonetheless, eosinophil research has traditionally focused on their role in anti-helminthic responses and pathophysiological processes in type-II immune disorders, such as allergy and asthma, where eosinophilia is a hallmark phenotype. However, a number of key studies over the past decade have placed this restricted view of eosinophil function into question, presenting additional evidence for eosinophils as critical regulators of various homeostatic processes including immune maintenance, organ development, and tissue regeneration.

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