title: Myelopoiesis in the thymus of the sea bass, Dicentrarchus labrax L. (teleost).
abstract: BACKGROUND
  In vertebrates the thymus is primarily regarded as a lymphoid organ whose importance lies in its capacity to produce a large number of lymphocytes that enter the circulation as T cells. In higher vertebrates the organ has also been regarded as a site for myelopoiesis, but this capacity has not been observed in fish. In this study we describe morphologically the presence of intrathymic developing myeloid cells in the sea bass.
  
  
  METHODS
  The thymus samples were morphologically studied by transmission electron microscopy.
  
  
  RESULTS
  We describe the coexistence of cells in different stages of erythropoiesis and granulopoiesis that appear to be developing in situ in some thymus lobes. Degenerated thymocytes and epithelial-reticular cells occur simultaneously in the same areas.
  
  
  CONCLUSIONS
  The coexistence of different cellular components of erythropoiesis and the heterophilic series of granulopoiesis with areas of necrosis suggests a relationship between both processes that is influenced by the microenvironment. Our observations also suggest that the presence of intrathymic developing myeloid cells may imply a nonimmunological role for the thymus.
authors.affiliation: Departamento de Biología Celular, Facultad de Biología, Universidad de Murcia, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Avilés-Trigueros
authors.forename: J A
authors.initials: JA
authors.lastname: Quesada
mesh_terms: D000818:Animals; D001492:Bass / Q000502:physiology*; D004920:Erythropoiesis; D005260:Female; D006098:Granulocytes / Q000166:cytology; D006411:Hematopoiesis, Extramedullary; D008297:Male; D009336:Necrosis; D013950:Thymus Gland / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure