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.
Itk Negatively Regulates Induction of T Cell Proliferation by CD28 Costimulation
Address correspondence to Dan R. Littman, Howard Hughes Medical Institute, Molecular Pathogenesis Program, The Skirball Institute of Biomolecular Medicine, second floor, New York University Medical Center, 540 First Avenue, New York 10016. Phone: 212-263-7579; FAX: 212-263-5711; E-mail: [email protected]. The current address for X.C. Liao is Tularik, Inc., Two Corporate Drive, South San Francisco, California 94080.
X.C. Liao and S. Fournier should be considered co–first authors of this study.
1Abbreviations used in this paper: CsA, cyclosporin A; IL-2Rα, interleukin-2 receptor α chain; JNK, c-Jun NH2 terminus kinase; PI3K, phosphatidylinositol 3′ kinase; PKC, protein kinase C; PLCγ1, phospholipase Cγ1.
X. Charlene Liao, Sylvie Fournier, Nigel Killeen, Arthur Weiss, James P. Allison, Dan R. Littman; Itk Negatively Regulates Induction of T Cell Proliferation by CD28 Costimulation. J Exp Med 21 July 1997; 186 (2): 221–228. doi: https://doi.org/10.1084/jem.186.2.221
Download citation file:
Sign in
Client Account
Sign in via your Institution
Sign in via your InstitutionSuggested Content
Email alerts
Advertisement