title: Cell lineage segregation during bursa of Fabricius ontogeny.
abstract: The population dynamics of myeloid and lymphoid lineages during bursa of Fabricius ontogeny were analyzed by immunofluorescence by using two monoclonal antibodies (mAb). CL-1 mAb reacts with all chicken hemopoietic cells, except mature erythrocytes. L22 mAb reacts with bursa and bursa-derived lymphocytes, with a minor subset of macrophages and with some cells of the thymic medulla. The staining of embryonic bursas by these antibodies helps to distinguish between two different lineages of hemopoietic cells: CL-1+/L22+ cells represent B lymphocytes and a minor subset of macrophages, while CL-1+/L22- cells correspond to most of the macrophages and to the granulocytes, which disappear at the end of the embryonic life. CL-1+/L22- as well as CL-1+/L22+ cells were first observed outside the bursal rudiment. This indicates that there is a pre-bursal segregation between these two hemopoietic lineages and that two different kinds of precursors colonize the bursal rudiment at about the same time (day 9 for CL-1+/L22- cells and days 9 or 10 for CL-1+/L22+ cells). Moreover our data show that the colonization of the bursal epithelium by hemopoietic precursors is a two-step phenomenon. The first cells which enter belong to the CL-1+/L22- lineage, express Ia-like antigens at a high level, are dendritic in morphology, and represent cells of the macrophage/dendritic cell lineage. They are responsible for the formation of the epithelial bud which are then colonized by a small number of lymphoid precursors which belong to the CL-1+/L22+ lineage. Quail-chick bursa grafting experiments were also performed and the grafts were examined for CL-1 (restricted to chicken hemopoietic cells) and L22 reactivity. These observations confirmed our previous findings about the kinetics of the colonization of bursal rudiment by hemopoietic precursors and give support for a pre-bursal segregation between two hemopoietic pathways.
authors.forename: E
authors.initials: E
authors.lastname: Houssaint
mesh_terms: D000367:Age Factors; D000818:Animals; D000911:Antibodies, Monoclonal; D001402:B-Lymphocytes / Q000166:cytology; D002060:Bursa of Fabricius / Q000166:cytology* / Q000254:growth & development / Q000276:immunology; D002454:Cell Differentiation; D002465:Cell Movement; D003370:Coturnix; D005455:Fluorescent Antibody Technique; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal