title: Replacement of pre-T cell receptor signaling functions by the CD4 coreceptor.
abstract: An important checkpoint in early thymocyte development ensures that only thymocytes with an in-frame T cell receptor for antigen beta (TCR-beta) gene rearrangement will continue to mature. Proper assembly of the TCR-beta chain into the pre-TCR complex delivers signals through the src-family protein tyrosine kinase p56lck that stimulate thymocyte proliferation and differentiation to the CD4+CD8+ stage. However, the biochemical mechanisms governing p56lck activation remain poorly understood. In more mature thymocytes, p56lck is associated with the cytoplasmic domain of the TCR coreceptors CD4 and CD8, and cross-linking of CD4 leads to p56lck activation. To study the effect of synchronously inducing p56lck activation in immature CD4-CD8- thymocytes, we generated mice expressing a CD4 transgene in Rag2-/- thymocytes. Remarkably, without further experimental manipulation, the CD4 transgene drives maturation of Rag2-/- thymocytes in vivo. We show that this process is dependent upon the ability of the CD4 transgene to bind Lck and on the expression of MHC class II molecules. Together these results indicate that binding of MHC class II molecules to CD4 can deliver a biologically relevant, Lck-dependent activation signal to thymocytes in the absence of the TCR-alpha or -beta chain.
authors.affiliation: Department of Immunology, University of Washington, Seattle 98195, USA.
authors.forename: A M
authors.initials: AM
authors.lastname: Norment
authors.forename: K A
authors.initials: KA
authors.lastname: Forbush
authors.forename: N
authors.initials: N
authors.lastname: Nguyen
authors.forename: M
authors.initials: M
authors.lastname: Malissen
authors.forename: R M
authors.initials: RM
authors.lastname: Perlmutter
mesh_terms: D000818:Animals; D015704:CD4 Antigens / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D016827:CD8 Antigens / Q000276:immunology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D017931:DNA Primers; D005434:Flow Cytometry; D015333:Gene Rearrangement, beta-Chain T-Cell Antigen Receptor; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008822:Mice, Transgenic; D016133:Polymerase Chain Reaction; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; D017931:DNA Primers; D016693:Receptors, Antigen, T-Cell, alpha-beta; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D019061:src-Family Kinases