title: Macrophages as novel target cells for erythropoietin.
abstract: BACKGROUND
  Our original demonstration of immunomodulatory effects of erythropoietin in multiple myeloma led us to the search for the cells in the immune system that are direct targets for erythropoietin. The finding that lymphocytes do not express erythropoietin receptors led to the hypothesis that other cells act as direct targets and thus mediate the effects of erythropoietin. The finding that erythropoietin has effects on dendritic cells thus led to the question of whether macrophages act as target cells for erythropoietin.
  
  
  METHODS
  The effects of erythropoietin on macrophages were investigated both in-vivo and in-vitro. The in-vivo studies were performed on splenic macrophages and inflammatory peritoneal macrophages, comparing recombinant human erythropoietin-treated and untreated mice, as well as transgenic mice over-expressing human erythropoietin (tg6) and their control wild-type counterparts. The in-vitro effects of erythropoietin on macrophage surface markers and function were investigated in murine bone marrow-derived macrophages treated with recombinant human erythropoietin.
  
  
  RESULTS
  Erythropoietin was found to have effects on macrophages in both the in-vivo and in-vitro experiments. In-vivo treatment led to increased numbers of splenic macrophages, and of the splenic macrophages expressing CD11b, CD80 and major histocompatibility complex class II. The peritoneal inflammatory macrophages obtained from erythropoietin-treated mice displayed increased expression of F4/80, CD11b, CD80 and major histocompatibility complex class II, and augmented phagocytic activity. The macrophages derived in-vitro from bone marrow cells expressed erythropoietin receptor transcripts, and in-vitro stimulation with erythropoietin activated multiple signaling pathways, including signal transducer and activator of transcription (STAT)1 and 5, mitogen-activated protein kinase, phosphatidylinositol 3-kinase and nuclear factor kappa B. In-vitro erythropoietin treatment of these cells up-regulated their surface expression of CD11b, F4/80 and CD80, enhanced their phagocytic activity and nitric oxide secretion, and also led to augmented interleukin 12 secretion and decreased interleukin 10 secretion in response to lipopolysaccharide.
  
  
  CONCLUSIONS
  Our results show that macrophages are direct targets of erythropoietin and that erythropoietin treatment enhances the pro-inflammatory activity and function of these cells. These findings point to a multifunctional role of erythropoietin and its potential clinical applications as an immunomodulating agent.
authors.affiliation: Department of Cell and Developmental Biology, histo6@post.tau.ac.il.
authors.forename: Lilach
authors.initials: L
authors.lastname: Lifshitz
authors.forename: Galit
authors.initials: G
authors.lastname: Tabak
authors.forename: Max
authors.initials: M
authors.lastname: Gassmann
authors.forename: Moshe
authors.initials: M
authors.lastname: Mittelman
authors.forename: Drorit
authors.initials: D
authors.lastname: Neumann
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000235:genetics; D018122:B7-1 Antigen / Q000096:biosynthesis / Q000235:genetics; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism*; D039481:CD11b Antigen / Q000096:biosynthesis / Q000235:genetics; D002478:Cells, Cultured; D004921:Erythropoietin / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D007155:Immunologic Factors / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D016753:Interleukin-10 / Q000096:biosynthesis / Q000235:genetics; D018664:Interleukin-12 / Q000096:biosynthesis / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D010587:Phagocytosis / Q000187:drug effects* / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D050799:STAT5 Transcription Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
chemical_list: D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D039481:CD11b Antigen; D000949:Histocompatibility Antigens Class II; D007155:Immunologic Factors; D008070:Lipopolysaccharides; D016328:NF-kappa B; D011994:Recombinant Proteins; D050794:STAT1 Transcription Factor; D050799:STAT5 Transcription Factor; C494080:Stat1 protein, mouse; C036763:monocyte-macrophage differentiation antigen; D004921:Erythropoietin; D016753:Interleukin-10; D018664:Interleukin-12; D019869:Phosphatidylinositol 3-Kinases; D020929:Mitogen-Activated Protein Kinase Kinases