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Prepublished online as a Blood First Edition Paper on May 8, 2003; DOI 10.1182/blood-2003-02-0449.
Blood, 1 September 2003, Vol. 102, No. 5, pp. 1654-1660 Hair follicles serve as local reservoirs of skin mast cell precursorsFrom the Departments of Dermatology and Ophthalmology, University of Texas Southwestern Medical Center, Dallas.
Several leukocyte populations normally reside in mouse skin, including
Langerhans cells and
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| Copyright © 2003 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
T cells in the epidermis and macrophage
and mast cells in the dermis. Interestingly, these skin resident leukocytes
are frequently identified within or around hair follicles (HFs), which are
known to contain stem cell populations that can generate the epidermal
architecture or give rise to the melanocyte lineage. Thus, we reasoned that
HFs might serve as a local reservoir of the resident leukocyte populations in
the skin. When vibrissal follicles of adult mice were cultured in the presence
of stem cell factor (SCF), interleukin 3 (IL-3), IL-7, granulocyte-macrophage
colony-stimulating factor, and Flt3 ligand,
CD45+/lineage–/c-kit+/Fc
RI+
cells became detectable on the outgrowing fibroblasts in 10 days and expanded
progressively thereafter. These HF-derived leukocytes showed characteristic
features of connective tissue-type mast cells, including proliferative
responsiveness to SCF, metachromatic granules, mRNA expression for mast cell
proteases-1, -4, -5, and -6, and histamine release on ligation of surface IgE
or stimulation with substance P or compound 48/80. These results, together
with our findings that HFs contain c-kit+ cells and produce SCF
mRNA and protein, suggest that HFs provide a unique microenvironment for local
development of mast cells. 
