UMR CNRS 7627, Hopital Pitié-Salpêtrière,
* Laboratoire de Virologie, Faculté de Médecine Cochin-Paris V; and
ESA 7087 UP6-CNRS and Laboratoire d’Immunologie et Immunopathologie de l’ Ecole Pratique des Hautes Etudes, Paris, France
Correspondence: Ali H. Dalloul, M.D., Ph.D., CERVI, Hopital Pitié-Salpêtrière, 83 Blvd. de l’Hopital, 75013, Paris, France. E-mail: dalloul{at}ccr.jussieu.fr
We have previously shown that thymic CD34+ cells have
a very limited myeloid differentiation capacity and differentiate
in vitro mostly into CD1a+-derived but not
CD14+-derived dendritic cells (DC). Herein we characterized
the human neonatal thymic DC extracted from the organ in relationship
with the DC generated from CD34+ cells in situ.
We show that in vivo thymic DC express E cadherin, CLA,
CD4, CD38, CD40, CD44, and granulocyte-macrophage colony-stimulating
factor-R (GM-CSF-R; CD116) but no CD1a. According to their morphology,
functions, and surface staining they could be separated into two
distinct subpopulations: mature HLA-DRhi, mostly
interleukin-3-R (CD123)-negative cells, associated with
thymocytes, some apoptotic, and expressed myeloid and activation
markers but no lymphoid markers. In contrast, immature
HLA-DR+ CD123hi CD36+ cells with
monocytoid morphology lacked activation and myeloid antigens but
expressed lymphoid antigens. The latter express pT
mRNA, which is
also found in CD34+ thymocytes and in blood
CD123hi DC further linking this subset to lymphoid DC.
However, the DC generated from CD34+ thymic progenitors
under standard conditions were pT-negative. Thymic lymphoid DC
showed similar phenotype and cytokine production profile as
blood/tonsillar lymphoid DC but responded to GM-CSF, and at variance
with them produced no or little type I interferon upon infection with
viruses and did not induce a strict polarization of naive T cells into
TH2 cells. Their function in the thymus remains therefore to be
elucidated.
Key Words: thymus • blood cells • tonsillar cells
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