Transforming Growth Factor (cid:98) 1, in the Presence of Granulocyte/Macrophage Colony-stimulating Factor and Interleukin 4, Induces Differentiation of Human Peripheral Blood Monocytes into Dendritic Langerhans Cells

Langerhans cells (LCs) are dendritic cells (DCs) that are present in the epidermis, bronchi, and mucosae. Although LCs originate in bone marrow, little is known about their lineage of origin. In this study, we demonstrate that in vitro LCs may originate from monocytes. Adult peripheral blood CD14 (cid:49) monocytes differentiate into LCs (CD1a (cid:49) , E-cadherin (cid:49) , cutaneous lympho-cyte-associated antigen (cid:49) , Birbeck granules (cid:49) , Lag (cid:49) ) in the presence of granulocyte/macrophage colony-stimulating factor, interleukin 4, and transforming growth factor (cid:98) 1 (TGF- (cid:98) 1). This process occurs with virtually no cell proliferation and is not impaired by 30 Gy irradiation. Selection of monocyte subpopulations is ruled out since monocyte-derived DCs can further differentiate into LCs. Our data suggest that in vivo LC differentiation may be induced periph-erally, from a nonproliferating myeloid precursor, i.e., the monocyte, in response to a TGF- (cid:98) 1–rich microenvironment, as found in the skin and epithelia. Therefore, the monocyte may represent a circulating precursor critical to the immune response in vivo. Dallas, TX). Ultrastructural Study. Cells to be processed for electron microscopy were fixed overnight at 4 (cid:56) C in 2.5% glutaraldehyde (Sigma Chemical Co.) in 0.1 M cacodylate buffer, pH 7.4, fol-lowed by postfixation for 1–2 h in 0.1 M cacodylate-buffered 2% osmium tetraoxide (Merck, Darmstadt, Germany). After dehydra-tion in a series of graded ethanol and propylene oxide solutions, cells were embedded in epoxy resin (Epon 812; TAAB, Janning, Vanves, France). Ultrathin sections were stained with uranyl acetate and lead citrate and examined with a JEOL.1200 EX2 electron mi-croscope (JEOL, Croissy sur Seine, France).