title: Phorbol esters and cAMP differentially regulate the expression of CD4 and CD8 in human thymocytes.
abstract: BACKGROUND
  Intrathymic development and selection of the T lymphocyte repertoire is restricted by the interactions of the T cell antigen receptor and CD4 or CD8 co-receptors with self major histocompatibility complex molecules. Positive or negative selection depends on a tight regulatory control of CD4 and CD8 expression. Determining the intracellular signals that differentially regulate the expression of CD4 and CD8 is important to understand the mechanisms that are implicated in selection of single positive CD4+CD8- or CD4-CD8+.
  
  
  RESULTS
  The present study shows that stimulation of human thymocytes by phorbol esters or cAMP result in a differential regulation of CD4 and CD8 expression, both at the mRNA and cell surface glycoprotein level.
  
  
  CONCLUSIONS
  The differential regulation of CD4 and CD8 gene expression suggests that the selective activation of protein kinase C (PKC) and cAMP-dependent protein kinases (PKA) may be required for the selection of single positive CD4+CD8- and CD4-CD8+ cells during Intrathymic differentiation.
authors.affiliation: Department of Immunology, Box 178, The University of Texas MD Anderson Cancer Center, USA. hmartine@mdanderson.org
authors.forename: Hector
authors.initials: H
authors.lastname: Martinez-Valdez
authors.forename: Vicente
authors.initials: V
authors.lastname: Madrid-Marina
authors.forename: Amos
authors.initials: A
authors.lastname: Cohen
mesh_terms: D015704:CD4 Antigens / Q000096:biosynthesis* / Q000235:genetics; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D016827:CD8 Antigens / Q000096:biosynthesis* / Q000235:genetics; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000276:immunology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D012333:RNA, Messenger / Q000378:metabolism; D016176:T-Lymphocyte Subsets / Q000276:immunology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013950:Thymus Gland / Q000166:cytology / Q000276:immunology*
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; D012333:RNA, Messenger; D000242:Cyclic AMP; D013755:Tetradecanoylphorbol Acetate