ROLE OF ITK IN THE DEVELOPMENT OF INNATE T CELLS
Open Access
- Author:
- Qi, Qian
- Graduate Program:
- Immunology and Infectious Diseases
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 17, 2009
- Committee Members:
- Avery August, Dissertation Advisor/Co-Advisor
Avery August, Committee Chair/Co-Chair
Biao He, Committee Member
Margherita Teresa Anna Cantorna, Committee Member
Pamela Hankey Giblin, Committee Member
Robert Paulson, Committee Member
Zhi Chun Lai, Committee Member - Keywords:
- gammadelta T cell
Itk structure
innate T cell
Itk
BiFC assay - Abstract:
- The Tec family of tyrosine kinases transduces signals from antigen and other receptors in cells of the hematopoietic system. Tec kinases are composed of five domains- PH, TH, SH2, SH3 and kinase domain, which distinguish them from other nonreceptor tyrosine kinases. The unique domain composition of Tec kinases indicates a distinct structure and mode of regulation. In particular, Itk plays an important role in modulating T cell development and activation. Itk is activated by receptors via a PI3 kinase mediated pathway, which results in recruitment of Itk to the plasma membrane via its PH domain. We show here that membrane localization of Itk results in the formation of clusters of at least 2 molecules within 80 angstroms of each other, which is dependent on the integrity of its PH domain. More importantly, these clusters of Itk molecules form in distinct regions of the plasma membrane as only receptors that recruit PI3K reside in the same membrane vicinity as the recruited Itk. Our results indicate that Itk forms membrane dimers and that receptors that recruit Itk do so to specific membrane regions. Although the structures of each domain of Itk have been determined, the full structure of Itk and other Tec kinases remain elusive. Models of Itk suggest either a head to tail dimer, with the SH2 domain interacting with the SH3 domain, or a folded monomer with the SH3 domain interacting with the proline rich region exists. We show here that in vivo Itk exists as a monomer, with the PH domain less than 80 Å from the C-terminus. Zn2+ coordinating residues in the TH domain, not the proline rich region control this intramolecular interaction. These data have implications for our understanding of Tec family kinase structure. Invariant natural killer T (iNKT) cells are a unique subset of innate T lymphocytes that are selected by CD1d. They have diverse immune regulatory functions via the rapid production of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4). In the absence of ITK and Txk, Tec family non-receptor tyrosine kinases, mice exhibit a significant defect in iNKT cell development. We now show here that although Itk is required for iNKT cell maturation, mice carrying an Itk mutant lacking its kinase domain, Tg(Lck-ItkΔKin)/Itk-/- , exhibit significant rescue of mature iNKT cells in the thymus compared with ITK null mice. Furthermore, this rescue correlates with the increased expression of CD122, and altered balance of two T-box transcription factor, T-bet and eomesodermin. These data indicate that ITK uses a scaffolding function in the signaling pathway leading to the maturation of iNKT cells, and indicate that the kinase activity of ITK is only partially required for maturation of iNKT cells. Itk is critical for the development of alphabeta T cells as well as differentiation of CD4+ T cells into Th2 cells. Itk null mice have defect to produce Th2 cytokines, however they paradoxically have significant elevations in serum IgE. Here we show that Itk null mice have increased numbers of gammadelta T cells in the thymus and spleen. This includes elevated numbers of CD4+ gammadelta T cell, the majority of which carry the Vgamma 1.1 and Vdelta 6.2/3 T cell receptor and exhibit distinct phenotype. The development of these CD4+ gammadelta T cells is T cell intrinsic, independent of either MHC class I or class II, and is favored during development in the absence of Itk. Itk null CD4+ gammadelta T cells secrete significant amounts of Th2 cytokines and can induce the secretion of IgE by WT B cells. Altogether, Itk plays important role in regulating gammadelta T cell development and function. The elevated IgE observed in Itk deficient mice is due to the enhanced development of CD4+ gammadelta T cells in the absence of Itk. CD4+ gammadelta T cells may therefore play critical roles in B cell IgE class switch.