title: An antagonist peptide mediates positive selection and CD4 lineage commitment of MHC class II-restricted T cells in the absence of CD4.
abstract: The CD4 coreceptor works together with the T cell receptor (TCR) to deliver signals to the developing thymocyte, yet its specific contribution to positive selection and CD4 lineage commitment remains unclear. To resolve this, we used N3.L2 TCR transgenic, RAG-, and CD4-deficient mice, which are severely impaired in positive selection, and asked whether altered peptide ligands can replace CD4 function in vivo. Remarkably, in the presence of antagonist ligands that normally deleted CD4+ T cells in wild-type mice, we induced positive selection of functional CD4 lineage T cells in mice deficient in CD4. We show that the kinetic threshold for positive and negative selection was lowered in the absence of CD4, with no evident skewing toward the CD8 lineage with weaker ligands. These results suggest that CD4 is dispensable as long as the affinity threshold for positive selection is sustained, and strongly argue that CD4 does not deliver a unique instructional signal for lineage commitment.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Henry
authors.initials: H
authors.lastname: Kao
authors.forename: Paul M
authors.initials: PM
authors.lastname: Allen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001854:Bone Marrow Cells / Q000276:immunology / Q000528:radiation effects; D015704:CD4 Antigens / Q000235:genetics / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism*; D019070:Cell Lineage / Q000276:immunology*; D049109:Cell Proliferation; D017931:DNA Primers; D005434:Flow Cytometry; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D007376:Interleukin-2 / Q000378:metabolism; D008024:Ligands; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012641:Selection, Genetic
chemical_list: D015704:CD4 Antigens; D017931:DNA Primers; D000949:Histocompatibility Antigens Class II; D007376:Interleukin-2; D008024:Ligands; D010455:Peptides; D011948:Receptors, Antigen, T-Cell