5-lipoxygenase expression in dendritic cells generated from CD34+ hematopoietic progenitors and in lymphoid organs

The 5-lipoxygenase (5-LO) pathway in human CD34+ hematopoietic progenitor cells, which were induced to differentiate into dendritic cells (DCs) by cytokines in vitro and in DCs of lymphoid tissues in situ, was examined. Extracts prepared from HPCs contained low levels of 5-LO or 5-LO–activating protein. Granulocyte-macrophage colony-stimulating factor (GM-CSF) plus tumor necrosis factor–α (TNF-α) promoted DC differentiation and induced a strong rise in 5-LO and FLAP expression. Fluorescence-activated cell sorter (FACS) analyses identified a major DC population coexpressing human leukocyte antigen (HLA)-DR/CD80 and monocytic or Langerhans cell markers. Transforming growth factor–β1 (TGF-β–1), added to support DC maturation, strongly promoted the appearance of CD1a+/Lag+ Langerhans-type cells as well as mature CD83+ DCs. TGF-β–1 further increased 5-LO and FLAP expression, recruited additional cells into the 5-LO+DC population, and promoted production of 5-hydroxyeicosatetraenoic acid and leukotriene B4 in response to calcium (Ca++) ionophore [A23187][1]. These in vitro findings were corroborated by 5-LO expression in distinct DC phenotypes in vivo. Scattered 5-LO and FLAP in situ hybridization signals were recorded in cells of paracortical T-lymphocyte–rich areas and germinal centers (GCs) of lymph nodes (LNs) and tonsil and in cells of mucosae overlying the Waldeyer tonsillar ring. 5-LO protein localized to both CD1a+ immature DCs and to CD83+ mature interdigitating DCs of T-lymphocyte–rich areas of LNs and tonsil. As DCs have the unique ability to initiate naive lymphocyte activation, our data support the hypothesis that leukotrienes act at proximal steps of adaptive immune responses. [1]: /lookup/external-ref?link_type=GEN&access_num=A23187&atom=%2Fbloodjournal%2F96%2F12%2F3857.atom