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  • Title: CD40 ligand expression is developmentally regulated in human thymocytes.
    Author: Fuleihan R, Ahern D, Geha RS.
    Journal: Clin Immunol Immunopathol; 1995 Jul; 76(1 Pt 1):52-8. PubMed ID: 7606868.
    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.
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