ROLE OF TEC FAMILY KINASE ITK IN REGULATING THE DEVELOPMENT OF T CELL SUBSETS
Open Access
- Author:
- Hu, Jianfang
- Graduate Program:
- Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 16, 2008
- Committee Members:
- Avery August, Committee Chair/Co-Chair
Biao He, Committee Member
Margherita Teresa Anna Cantorna, Committee Member
Robert Paulson, Committee Member
Na Xiong, Committee Member
Wendy Hanna Rose, Committee Member - Keywords:
- Innate T cell
Memory phenotype T cell
Itk
Tec family kinases
Listeria Monocytogenes
CD4/CD8 lineage commitment - Abstract:
- T cells with a memory like phenotype and possessing innate immune function have been previously identified. These cells rapidly secrete IFN upon stimulation with IL-12/IL-18 and are involved in innate responses to infection with Listeria monocytogenes. The signals regulating these cells are unclear. The Tec kinase Itk regulates T cell activation, and we report here that a majority of the CD8+ T cells in Itk null mice have a phenotype of CD44hi similar to memory like innate T cells. These cells are observed in mice carrying an Itk mutant lacking the kinase domain, indicating that active Tec kinase signaling suppresses their presence. These cells carry preformed message for IFNγ and are able to rapidly produce IFN upon stimulation in vitro with IL-12/IL-18, and endow Itk null mice the ability to effectively respond to infection with L. monocytogenes or exposure to LPS by secretion of IFN. Transfer of these cells rescues the ability of IFN null mice to reduce bacterial burden following L. monocytogenes infection indicating that these cells are functional CD8+CD44hi T cells previously detected in vivo. These results indicate that active signals from Tec kinases regulate the development of memory like CD8+ T cells with innate function. In addition to regulating the development of conventional and innate CD8+ T cells, the Tec family kinase Itk also regulates the development of CD4+ T cell lineages. We show here that Itk null mice have increased percentage of CD62LLoCD44Hi memory phenotype CD4+ T cells compared to WT mice. These cells can arise directly in the thymus, but do not require this organ for their development. Instead MP CD4+ T cell development is bone marrow derived MHC Class II dependent, and independent of MHC Class II expression on the thymic epithelium. These cells express high levels of transcripts for the T-bet and IFNγ and are able to produce IFNγ directly ex vivo in response to stimulation. Itk deficiency greatly decreases the number of CD4+ T cells with CD62LHiCD44Lo naïve phenotype, but has no effect on the number of memory phenotype CD4+ T cells, indicating that the development of memory phenotype CD4+ T cells is Itk independent. We further show that the development of the naïve phenotype CD4+ T cells is dependent on active Itk kinase signals and can be rescued by expression of Itk specifically in T cells, but not the Txk overexpression. Itk is required for functional TCR signaling in these cells, but not for the innate function in response to IL-12/IL-18 or L. monocytogenes stimulation. These results indicate that CD62LHiCD44Lo “naïve” and CD62LLoCD44Hi “innate memory phenotype” CD4+ T cells may be independent populations that differ in their requirement for Itk’s signals for development. Our data also suggest that CD4+CD62LLoCD44Hi memory phenotype T cells have innate immune function. We have also examined whether CD4/CD8 lineage choice is affected by a combination of TCR affinity and Itk by analyzing mice lacking Itk and carrying the low affinity TCR transgene OT-II, specific for a peptide in Ovalbumin. Our results show that OT-II/Itk-/- thymocytes receive reduced TCR signals, with a reduction in CD4+ T cell development. Surprisingly, these mice develop significant numbers of MHC class II restricted TCR transgenic CD8+ T cells that resemble non-conventional or innate memory phenotype CD8 T cells. We also show that the development of these class II-restricted innate memory phenotype CD8+ T cells is bone marrow intrinsic, and may be the result of reduced TCR signaling in the absence of Itk resulting in reduced expression of the transcription factor, Th-POK, a master regulator of CD4 commitment. All together, these data suggest that Itk plays an important role in CD4/CD8 commitment by regulating signal thresholds for the lineage commitment. Our data also suggest that the lower level of TCR signaling that occurs with a low affinity TCR in the absence of Itk can redirect MHC class II restricted CD4+ T cell to develop into class II-restricted CD8+ innate memory phenotype T cells. Overall our results suggest that loss of Itk differentially affects the development of conventional vs. non-conventional MP T cells and also plays important roles in CD4/CD8 lineage commitment.