title: CD40 ligand expression is developmentally regulated in human thymocytes.
abstract: Thymic selection involves the interaction between developing thymocytes and the thymic microenvironment. CD40 is expressed on thymic epithelial cells and on bone marrow-derived antigen-presenting cells in the thymus. We have investigated the capacity of human thymocytes to express CD40 ligand. CD40 ligand was not detectable on resting immature double-positive (CD4+/CD8+) or resting mature single-positive (CD4+/CD8- or CD4-/CD8+) thymocytes. Immature thymocytes failed to express CD40 ligand on their surface after stimulation with PMA and ionomycin, whereas stimulated CD4+/CD8- mature thymocytes expressed CD40 ligand. Northern blot analysis revealed that CD40 ligand mRNA was detectable in activated mature single-positive thymocytes. CD40 ligand expression by mature thymocytes was associated with the capacity to drive immunoglobulin isotype switching in purified B cells. These results demonstrate that the ability to express CD40 ligand is acquired late in thymocyte development and that mature thymocytes are capable of providing B cells with the activation signals necessary for immunoglobulin isotype switching.
authors.affiliation: Division of Immunology, Children's Hospital, Boston, Massachusetts 02115, USA.
authors.forename: R
authors.initials: R
authors.lastname: Fuleihan
authors.forename: D
authors.initials: D
authors.lastname: Ahern
authors.forename: R S
authors.initials: RS
authors.lastname: Geha
mesh_terms: D015703:Antigens, CD / Q000302:isolation & purification; D001402:B-Lymphocytes / Q000276:immunology; D015139:Blotting, Southern; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D023201:CD40 Ligand; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D002675:Child, Preschool; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D006801:Humans; D017578:Immunoglobulin Class Switching; D007073:Immunoglobulin E / Q000032:analysis; D007223:Infant; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013950:Thymus Gland / Q000166:cytology / Q000254:growth & development* / Q000276:immunology
chemical_list: D015703:Antigens, CD; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D023201:CD40 Ligand; D007073:Immunoglobulin E