title: Reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.): an ultrastructural and cytochemical study.
abstract: BACKGROUND
  Head-kidney, considered the major fish lympho-haemopoietic tissue, consists of cells of the different haemopoietic series supported by a network of stromal cells whose morphofunctional properties have not been established. We report the ultrastructure and cytochemical features of the reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.).
  
  
  METHODS
  Samples of head-kidney were processed for electron microscopic study. Some of the samples were incubated for acid and alkaline phosphatase, peroxidase, glucose-6-phosphatase, or ATPase.
  
  
  RESULTS
  The reticulo-endothelial stroma of gilthead seabream head-kidney consists of sinusoidal cells (endothelial and adventitial cells) and reticular cells (macrophage-type reticulum and fibroblast-like reticular cells). Transcytosis vesicles and rounded medium electron-dense granules were observed in the cytoplasm of the endothelial cells. The adventitial cells partially covered the outside surface of the endothelial cells and were joined by desmosomes. The macrophage-type reticulum cells were characterized by their cytoplasmic processes and acid phosphatase positive lysosomes. The fibroblast-like reticular cells were joined by desmosomes and formed an extensive network between the haemopoietic parenchyma. They were peroxidase negative and acid and alkaline phosphatase, glucose-6-phosphatase, beta-glucuronidase, and ATPase positive.
  
  
  CONCLUSIONS
  The ultrastructural and cytochemical features of the reticulo-endothelial stroma of the gilthead seabream head-kidney are similar to those of mammalian bone marrow, suggesting phylogenetic analogies between both tissues.
authors.affiliation: Department of Cell Biology, Faculty of Biology, University of Murcia, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Meseguer
authors.forename: A
authors.initials: A
authors.lastname: López-Ruiz
authors.forename: A
authors.initials: A
authors.lastname: García-Ayala
mesh_terms: D000818:Animals; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D012157:Mononuclear Phagocyte System / Q000166:cytology / Q000648:ultrastructure*; D010473:Perciformes / Q000033:anatomy & histology*