title: Bone marrow accessory cells regulate human bone precursor cell development.
abstract: OBJECTIVE
  Much remains to be learned about the intimate relationship between bone marrow and its surrounding tissue: the bone. We hypothesized that bone marrow accessory cell populations might regulate the development of human bone precursor cells.
  
  
  METHODS
  We used immunologic phenotyping, and isolation methods to fractionate subpopulations of nonadherent, low-density (NALD) human bone marrow cells. These cells were examined for their ability to support the serum-free survival, proliferation, and expression of bone proteins by highly purified populations of human bone precursor cells. Quantitative assessment of the accessory cell populations as well as human bone precursor cells phenotype was performed using multiparameter flow cytometry. Bone protein expression was evaluated by immunocytochemistry, Western analysis, and enzymatic analysis (for alkaline phosphatase activity).
  
  
  RESULTS
  Human bone marrow contains a cell population that stimulates the development of purified bone precursor cells. Feeder-layer studies demonstrate that these osteopoietic accessory cells (OACs) do not require cell-cell interaction to promote bone precursor cell development but, rather, produce soluble molecules responsible for their effects. Flow cytometric analyses reveal that bone marrow derived B cells, T cells, macrophages, natural killer cells, and endothelial cells do not produce this stimulatory factor. The (growth) factor cannot be replaced by addition of exogenous cytokines. The isolation of human transforming growth factor beta receptor type II (TGF-betaRII)-positive cells increases OAC-specific activity in bone cell ex vivo expansion cultures. Moreover, isolation of OAC bone marrow cells characterized by high TGF-betaRII expression, relatively low cellular complexity, and small size yields a population that is highly enriched for OACs.
  
  
  CONCLUSIONS
  We conclude that human bone marrow contains a population of OACs that are an obligate requirement for the early phases of bone cell development ex vivo.
authors.affiliation: Department of Pediatrics, University of Michigan, Ann Arbor, USA.
authors.forename: P G
authors.initials: PG
authors.lastname: Eipers
authors.forename: S
authors.initials: S
authors.lastname: Kale
authors.forename: R S
authors.initials: RS
authors.lastname: Taichman
authors.forename: G G
authors.initials: GG
authors.lastname: Pipia
authors.forename: N A
authors.initials: NA
authors.lastname: Swords
authors.forename: K G
authors.initials: KG
authors.lastname: Mann
authors.forename: M W
authors.initials: MW
authors.lastname: Long
mesh_terms: D000938:Antigen-Presenting Cells / Q000502:physiology*; D001854:Bone Marrow Cells / Q000502:physiology*; D002448:Cell Adhesion; D002469:Cell Separation; D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis; D005434:Flow Cytometry; D006801:Humans; D016130:Immunophenotyping; D010006:Osteoblasts / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D016207:Cytokines; D018125:Receptors, Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II