title: Characterization of colony-forming cells in the human thymus: evidence for a suppressor mechanism.
abstract: Activation pathways for thymic cell growth remain partially unknown. Thymocytes generally show low growth responses when cultured in the presence of mitogens, especially when T-cell colony formation by these cells is assayed. In the present work we studied the T-cell colony-forming ability of thymic subsets under phytohemagglutinin (PHA) and/or recombinant interleukin 2 (rIL2) stimulation. Our results confirm the low number of T-cell colonies obtained from human thymus as compared to bone marrow and peripheral blood sources. In contrast, significant colony numbers were observed when thymocytes were depleted of CD8+ cells. This increase was due to the suppression exerted by CD8+ cells on both CD4+- and CD4- -, CD8- -derived colony precursors. This inhibitory mechanism is dose-dependent and cannot be replaced by media conditioned by CD8+ cells. Limiting dilution analysis corroborates agar assays and points to the existence of T-cell colony-forming cells within the double-negative (CD4-, CD8-) thymic subset.
authors.affiliation: Department of Cellular Immunology, Pitié Salpétrière Hospital, Paris, France.
authors.forename: A H
authors.initials: AH
authors.lastname: Dalloul
authors.forename: M D
authors.initials: MD
authors.lastname: Mossalayi
authors.forename: J M
authors.initials: JM
authors.lastname: Bertho
authors.forename: G
authors.initials: G
authors.lastname: Courboin
authors.forename: P
authors.initials: P
authors.lastname: Debré
mesh_terms: D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D001854:Bone Marrow Cells; D002454:Cell Differentiation; D002455:Cell Division / Q000187:drug effects; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D007108:Immune Tolerance; D066298:In Vitro Techniques; D007376:Interleukin-2 / Q000494:pharmacology; D007963:Leukocytes, Mononuclear / Q000166:cytology; D013601:T-Lymphocytes / Q000145:classification / Q000166:cytology*; D050378:T-Lymphocytes, Regulatory / Q000166:cytology; D013950:Thymus Gland / Q000166:cytology*
chemical_list: D000911:Antibodies, Monoclonal; D000945:Antigens, Differentiation, T-Lymphocyte; D007376:Interleukin-2