title: Ontogeny of ramified CD45 cells in chicken embryo and their contribution to bursal secretory dendritic cells.
abstract: Embryonic tissues contain highly ramified stellate-shaped cells expressing CD45 and MHC II antigens but their origin and immunophenotype are unknown. Using staged avian embryos and cell-type-specific antibodies, we establish a detailed spatiotemporal ontogeny of cells that express CD45, the earliest marker of hematopoietic stem cells in the chick. CD45 immunostaining marks three distinct embryonic cell populations: round, ramified and amoeboid cells. The round and ramified CD45+ cells appear first in yolk-sac blood islands before the onset of circulation. A subpopulation of round cells co-expresses the thrombocyte-specific CD51/CD61 antigen. Amoeboid cells express macrophage-specific antigens and frequently occur in regions of apoptosis. Ramified cells are distributed uniformly in the embryonic mesenchyme, colonize lymphoid and non-lymphoid organs and later express MHC II. To study the origin of CD45+ cells, 2-day-old chick embryos were ablated from the yolk sac before the establishment of circulation and incubated for 2-5 days. Large numbers of CD45+MHC II+ ramified cells differentiated in the yolk sac. Yolk-sac chimeras were generated by grafting embryos into GFP-expressing de-embryonated yolk sacs. GFP/CD45 co-expressing ramified and amoeboid cells colonized all organ primordia in the donor embryo. We also recombined GFP+ yolk sac with the bursa of Fabricius and found ramified GFP+CD45+ cells in the bursa where they differentiated into dendritic cells. Thus, CD45 cells are first present in the yolk sac during primitive hematopoiesis and then migrate from the extra-embryonic yolk sac to give rise to cells throughout all organ primordia, including dendritic cells in the bursa of Fabricius.
authors.affiliation: Department of Anatomy, Histology and Embryology, Faculty of Medicine, Semmelweis University, 58 Tűzoltó Street, Budapest, 1094, Hungary.
authors.forename: Dávid
authors.initials: D
authors.lastname: Dóra
authors.affiliation: Department of Anatomy, Histology and Embryology, Faculty of Medicine, Semmelweis University, 58 Tűzoltó Street, Budapest, 1094, Hungary.
authors.forename: Nóra
authors.initials: N
authors.lastname: Fejszák
authors.affiliation: Department of Pediatric Surgery, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA.
authors.forename: Allan M
authors.initials: AM
authors.lastname: Goldstein
authors.affiliation: Department of Anatomy, Histology and Embryology, Faculty of Medicine, Semmelweis University, 58 Tűzoltó Street, Budapest, 1094, Hungary.
authors.forename: Krisztina
authors.initials: K
authors.lastname: Minkó
authors.affiliation: Department of Anatomy, Histology and Embryology, Faculty of Medicine, Semmelweis University, 58 Tűzoltó Street, Budapest, 1094, Hungary. nagy.nandor@med.semmelweis-univ.hu.|Department of Pediatric Surgery, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA. nagy.nandor@med.semmelweis-univ.hu.
authors.forename: Nándor
authors.initials: N
authors.lastname: Nagy
mesh_terms: D000818:Animals; D002060:Bursa of Fabricius / Q000166:cytology*; D002454:Cell Differentiation; D002642:Chick Embryo; D003713:Dendritic Cells / Q000166:cytology / Q000378:metabolism*; D006412:Hematopoietic Stem Cells; D017493:Leukocyte Common Antigens / Q000378:metabolism*; D008214:Lymphocytes / Q000166:cytology; D022423:Myeloid Cells / Q000166:cytology; D010641:Phenotype; D015017:Yolk Sac / Q000166:cytology / Q000378:metabolism
chemical_list: D017493:Leukocyte Common Antigens
keywords: Bursa of Fabricius; Dendritic cells; Hematopoiesis; Macrophages; Yolk sac