title: Differential effects of Flk-2/Flt-3 ligand and stem cell factor on murine thymic progenitor cells.
abstract: Most primitive thymic progenitors, termed CD4(low) cells (CD25- CD44+ CD117+), retain the ability to generate multiple lymphoid lineages. T cell lineage commitment occurs as CD4(low) cells differentiate into pro-T cells (CD25+ CD44+ CD117+). We previously reported that the in vitro cytokine responses of CD4(low) and pro-T cells differ. While Flt-3 ligand (Flt-3L) has been shown to be involved in early bone marrow hemopoiesis, its role in thymopoiesis has not been thoroughly examined. Here, we report that Flt-3L has no significant effect on pro-T cells, either by in vitro proliferation or in fetal thymic organ culture repopulation. In contrast, CD4(low) cells cultured in vitro for 3 days in IL-3 + IL-6 + IL-7 + Flt-3L generated a twofold increase in cell number 21 days after transfer into fetal thymic organ culture that increased to sixfold by day 35 when compared with the corresponding CD4(low) cells cultured in IL-3 + IL-6 + IL-7 + stem cell factor. Additionally, the Flt-3L-cultured CD4(low) cells displayed fetal thymic organ culture repopulation kinetics that more closely approximated those seen with freshly isolated CD4(low) cells. These data suggest that Flt-3L serves as a self-renewal or proliferation/expansion signal for CD4(low) cells, while the effect of stem cell factor is more likely to transduce a differentiation signal, resulting in more rapid repopulation at the expense of cell expansion.
authors.affiliation: Immunology Department, DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, CA 94304, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Moore
authors.forename: A
authors.initials: A
authors.lastname: Zlotnik
mesh_terms: D000818:Animals; D016207:Cytokines / Q000494:pharmacology*; D006410:Hematopoiesis; D007377:Interleukin-3 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D015851:Interleukin-7 / Q000494:pharmacology; D008565:Membrane Proteins / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009924:Organ Culture Techniques; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D019089:Stem Cell Factor / Q000502:physiology*; D013950:Thymus Gland / Q000166:cytology* / Q000196:embryology; D013997:Time Factors; D051941:fms-Like Tyrosine Kinase 3
chemical_list: D016207:Cytokines; D007377:Interleukin-3; D015850:Interleukin-6; D015851:Interleukin-7; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019089:Stem Cell Factor; C084881:flt3 ligand protein; C497971:Flt3 protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D051941:fms-Like Tyrosine Kinase 3