title: Exogenous IL-7 promotes the growth of CD3-CD4-CD8-CD44+CD25+/- precursor cells and blocks the differentiation pathway of TCR-alpha beta cells in fetal thymus organ culture.
abstract: Addition of human rIL-7 to fetal thymic organ culture started at day 13, 14, or 15 did not influence the number of cells generated during a 12-day culture period. However, the IL-7 treatment resulted in a preferential expansion of cells with a phenotype characteristic for cells at an early step of differentiation. The cells were CD4-CD8-CD3-CD2- and SCA-1+. Analysis of the coordinate expression of CD44 and CD25 on these cells showed that the majority of the cells were either CD44+CD25- or CD44+CD25intermediate. TCR-alpha beta cells were present but in a significantly lower number as compared to the control cultures. The cell number of TCR-gamma delta cells was increased. All these effects were moderate after 6 days, but unequivocal after 12 days of culture. Treatment of the fetal organ culture with mAb-neutralizing murine IL-7 resulted in an inhibition of the proliferation of the fetal thymocytes. No particular subset studied was preferentially inhibited. By using a model of reconstitution of 14-day embryonic thymuses depleted of thymocytes by deoxyguanosine and reconstituted with fetal day 13 liver cells and set up in organ culture with or without IL-7, it was shown in a clear cut way that IL-7 indeed promotes expansion of the early precursor cells and TCR-gamma delta cells, but prevents the generation of TCR-alpha beta cells. In addition, reconstitution experiments were set up in the presence of mAb-neutralizing murine IL-7. This treatment resulted in the inhibition of the growth of the fetal thymocytes without inhibiting preferentially a particular subset. These data indicate that IL-7 acts at an early step of T cell differentiation and plays a role to expand precursor cells, but prevents this population from additional differentiation towards the TCR-alpha beta pathways, whereas the differentiation towards TCR-gamma delta cells is not influenced or even enhanced.
authors.affiliation: Department of Bacteriology, Virology and Immunology, University Hospital Gent, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Plum
authors.forename: M
authors.initials: M
authors.lastname: De Smedt
authors.forename: G
authors.initials: G
authors.lastname: Leclercq
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000032:analysis*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D000950:Antigens, Ly / Q000378:metabolism; D018801:CD2 Antigens; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D002454:Cell Differentiation / Q000187:drug effects / Q000276:immunology; D002455:Cell Division / Q000187:drug effects / Q000276:immunology; D048429:Cell Size / Q000276:immunology; D005333:Fetus; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000276:immunology; D015851:Interleukin-7 / Q000494:pharmacology*; D007958:Leukocyte Count / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009924:Organ Culture Techniques; D010641:Phenotype; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology*; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism; D015375:Receptors, Interleukin-2; D016201:Receptors, Lymphocyte Homing; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000276:immunology; D013950:Thymus Gland / Q000166:cytology*
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D000950:Antigens, Ly; D018801:CD2 Antigens; D017252:CD3 Complex; D015704:CD4 Antigens; D016827:CD8 Antigens; D015851:Interleukin-7; C074650:Ly6a protein, mouse; D008565:Membrane Proteins; D016693:Receptors, Antigen, T-Cell, alpha-beta; D016692:Receptors, Antigen, T-Cell, gamma-delta; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2; D016201:Receptors, Lymphocyte Homing