title: Itk negatively regulates induction of T cell proliferation by CD28 costimulation.
abstract: CD28 is a cell surface molecule that mediates a costimulatory signal crucial for T cell proliferation and lymphokine production. The signal transduction mechanisms of CD28 are not well understood. Itk, a nonreceptor protein tyrosine kinase specifically expressed in T cells and mast cells, has been implicated in the CD28 signaling pathway because of reports that it becomes phosphorylated on tyrosines and associates with CD28 upon cross-linking of the cell surface molecule. To determine whether Itk plays a functional role in CD28 signaling, we compared T cells from Itk-deficient mice and control mice for their responses to CD28 costimulation. T cells defective in Itk were found to be fully competent to respond to costimulation. Whereas the CD3-mediated proliferative response was severely compromised in the absence of Itk, the calcineurin-independent CD28-mediated response was significantly elevated when compared with cells from control animals. The augmented proliferation was not due to increased production of interleukin-2. The results suggest that Itk has distinct roles in the CD3 versus the CD28 signaling pathways. By negatively regulating the amplitude of signaling upon CD28 costimulation, Itk may provide a means for modulating the outcome of T cell activation during development and during antigen-driven immune responses.
authors.affiliation: Department of Microbiology and Immunology, University of California, San Francisco, California 94143, USA.
authors.forename: X C
authors.initials: XC
authors.lastname: Liao
authors.forename: S
authors.initials: S
authors.lastname: Fournier
authors.forename: N
authors.initials: N
authors.lastname: Killeen
authors.forename: A
authors.initials: A
authors.lastname: Weiss
authors.forename: J P
authors.initials: JP
authors.lastname: Allison
authors.forename: D R
authors.initials: DR
authors.lastname: Littman
mesh_terms: D000818:Animals; D018106:CD28 Antigens / Q000502:physiology*; D007376:Interleukin-2 / Q000502:physiology; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011948:Receptors, Antigen, T-Cell / Q000502:physiology; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D018106:CD28 Antigens; D007376:Interleukin-2; D011948:Receptors, Antigen, T-Cell; D011505:Protein-Tyrosine Kinases; C080813:emt protein-tyrosine kinase