International Immunology, Vol. 15, No. 9, pp. 1105-1116,
September 2003
© 2003 Japanese Society for Immunology
Death of T cell precursors in the human thymus: a role for CD38
Sections of 1 Human Anatomy and 2 Histology, Department of Experimental Medicine, and 3 Department of Biophysics and Dental Sciences, University of Genova, 16132 Genova, Italy 4 Cancer Research Institute, Genova, Italy 5 Institute of Immunology and Infectious Diseases, University of Verona, Verona, Italy 6 Laboratory of Immunogenetics, University of Torino, Torino, Italy
The first two authors contributed equally to this work
Correspondence to: C. E. Grossi, Department of Experimental Medicine, Institute of Human Anatomy, University of Genova, Via De Toni 14, 16132 Genova, Italy. E-mail: anatuman{at}unige.it
Transmitting editor: S. Izui
Thymic T cell maturation depends on interactions between thymocytes and cells of epithelial and hematopoietic lineages that control a selective process whereby developing T cells with inappropriate or self-reactive receptors die. Molecules involved in this process are the TCR expressed on thymocytes together with the CD3 complex and MHC–peptide on accessory cells. However, other molecules may favor or prevent death of thymocytes, thus playing a role in selection. CD38 is expressed by the majority of human thymocytes, mainly at the double-positive (DP) stage. In contrast, CD38 is not found on subcapsular double-negative (DN) thymocytes and on a proportion of medullary single-positive (SP) thymocytes. CD38 enhances death of thymocytes when it is cross-linked by goat anti-mouse (GAM) antiserum or by one of its ligands, CD31, expressed by thymic epithelial cells or transfected into murine fibroblasts (L cells). As most thymocytes are at an intermediate (DP) stage of development, it is likely that these cells are most vulnerable to death mediated via MHC–peptide–TCR interactions that is increased by CD38 cross-linking. DN and SP thymocytes are refractory to CD38-induced apoptosis. Accessory molecules, e.g. CD38, are expressed during thymic cell maturation and their presence is relevant for the survival or death of DP T cells in the course of selection. Based on our data, CD38 enhances thymocyte death by interacting with CD31 expressed by accessory cells. In addition, CD28 expression on developing thymocytes also appears to play a role for their selection and it synergizes with CD38 to induce apoptosis of DP thymocytes.
Keywords: CD31, CD38, apoptosis, thymocytes