Eosinophils play an important role in the pathogenesis of allergic reactions or chronic inflammatory diseases by releasing various types of cytokines and chemical mediators. Recently, we have identified murine eosinophil-committed progenitors (mEoPs) in mouse bone marrow. The expression of receptor for IL-5, a critical cytokine for proliferation and differentiation of eosinophils, was a key marker to isolate mEoPs: mEoP was IL-5Ra+Lineage(lin)-CD34+c-Kitlow population in murine bone marrow (

J Exp Med.
201
,
1891ndash
;7,
2005
). Here we report that EoPs are prospectively isolatable also in human bone marrow. We analyzed the expression of human IL-5Ra in human stem and progenitor populations, and found that a fraction of common myeloid progenitor (CMP; lin-CD34+CD38+CD45RA-IL-3Ra+) population expressed hIL-5Ra on their surface by using anti-human IL-5Ra monoclonal antibodies. IL-5Ra protein and mRNA were undetectable in hematopoietic stem cells (HSCs; lin-CD34+CD38-), common lymphoid progenitors (CLPs; lin-CD34+CD38+CD10+), megakaryocyte/erythrocyte progenitors (MEPs; lin-CD34+CD38+CD45RA-IL-3Ra-), or granulocyte/monocyte progenitors(GMPs; lin-CD34+CD38+CD45RA+IL-3Ra+) by FACS and RT-PCR, respectively. The IL-5Ra+ cells within the CMP fraction constituted only ~0.04% of steady-state bone marrow mononuclear cells, and gave rise only to pure eosinophil colonies. Thus we termed this population as human EoP (hEoP). Both HSCs and the IL-5Ra- fraction of CMPs gave rise to IL-5Ra+ hEoPs in vitro in the presence of IL-3 and GM-CSF, while MEPs or GMPs never generated hEoPs, indicating that human eosinophil pathway diverges at the CMP stage, and that the eosinophil potential was lost at the GMP or MEP stage. Accordingly, the human eosinophil pathway is different from that in murine hematopoiesis where mEoPs develop from the GMP stage. Strikingly, the number of hEoPs in the bone marrow of patients with hypereosinophilic syndrome was significantly (~4-fold) increased as compared to that in normal bone marrow, suggesting that hEoP represents a critical stage for eosinophilia in vivo. Thus, the hEoP is an attractive candidate for therapeutic target in eosinophil-related allergic and inflammatory disorders. This population might also be very useful to study the molecular mechanism of human eosinophil development.

Topics:
cd34 antigens, cyclic gmp, cytokine, disseminated eosinophilic collagen disease, eosinophilia, eosinophils, granulocyte-macrophage colony-stimulating factor, hypersensitivity, inflammatory disorders, interleukin-3

Disclosure: No relevant conflicts of interest to declare.

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2006, The American Society of Hematology
2006
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