The Journal of immunology : official journal of the American Association of Immunologists
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Human mast cells (MC) were derived from umbilical cord blood and bone marrow progenitors cultured in the presence of a conditioned medium from a human mastocytosis cell strain and recombinant human kit ligand. MCs were studied using a sequential double immunoenzymatic analysis to determine the heterogeneity of expression of tryptase and chymase, two MC-specific proteases. The conditioned medium and kit ligand promoted the development of distinct MC subtypes from bone marrow and umbilical cord blood progenitors. kit ligand induced MC from umbilical cord blood predominantly of two immunophenotypes, MCT positive for tryptase but negative for chymase, and MCTC positive for tryptase and chymase. ⋯ In bone marrow cultures supplemented with conditioned medium alone, the MCC subtype represented 100% of the MCs on day 10 of culture. This study clearly demonstrates that a third type of MC, MCC, expressing chymase without concomitant expression of tryptase can be induced in vitro from normal human progenitors. In addition, it shows that tryptase and chymase, two MC-specific proteases, can be differentially expressed in in vitro derived human MCs by changing the cytokine combination of the culture.
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In the neonatal human thymus, early immature precursors co-express CD34 and CD7 cell surface Ags, and we have recently shown that its most primitive CD34+7+1- fraction includes TCR-beta-rearranging cells. Bone marrow and cord blood also contain a CD34+7+ population. Although this population is heterogeneous in terms of both phenotype and differentiation capacities, it may include T cell-committed thymus colonizing precursors (prothymocytes). ⋯ Furthermore, whereas none of the CD34+ cord blood cell fraction expressed TCR-alpha transcripts, mature V(delta)1-C(delta) mRNA could be amplified from the CD34+7+ subset. The TdT gene was also transcriptionally active in CD34+7+ cells, thus confirming their lymphoid progenitor content. These data indicate that cord blood CD34+7+ cells, like CD34+7+1- neonatal thymocytes, can initiate TCR-beta gene recombination, reinforcing the idea that T cell commitment may occur before prothymocyte migration to the thymus.