B. J. Fowlkes, Ph.D.
Chief, T Cell Development Section, LI
T lymphocytes perform important roles in the immune system by regulating specific immune responses or by directly killing pathogen-infected or cancer cells. The goal of the T Cell Development Section (TCDS) is to investigate mechanisms controlling cell fate decisions in developing and mature T cells (Fig. 1A, B). These decisions are guided by intrinsic and environmental cues, such as those that signal through the T-cell antigen receptor (TCR) and other surface receptors like the highly conserved Notch receptor. T-cell development in the thymus involves stringent selection processes that promote the generation of useful T cells and eliminate self-reactive T cells in order to prevent autoimmunity. TCR engagement of peptides bound to major histocompatibility complexes, MHC1 or MHC2, in the process of thymic selection also facilitates commitment of immature thymocytes to the CD8 or CD4 T-cell lineages. In the periphery, signals from the TCR and costimulatory molecules collectively determine whether a mature T cell will reach the threshold for activation, commit to proliferation, and acquire specialized effector functions. Thus, a major aim of the TCDS has been to elucidate key signaling pathways that mediate T-cell activation, differentiation, and lineage commitment. Advances in T-cell development are fundamental to understanding how immune responses are generated and have important applications for diagnosing, treating, and preventing human disease.
Initial accomplishments of the TCDS were in the characterization of early thymocyte precursors, thymocyte subsets, precursor/product relationships, TCR expression, and functional maturation. The section also made contributions to understanding mechanisms regulating thymocyte selection and lineage commitment.
The long-term focus of the laboratory has been to understand how TCR signaling promotes differentiation and the development of T-cell lineages. A critical early checkpoint in thymocyte development is imposed by surface expression of the preTCR, consisting of the TCRβ chain and the invariant preTCRα (pTα) chain. To study the signaling potential of the pTα tail under physiological conditions, we used a knock-in gene targeting approach to replace the endogenous locus with a truncated gene encoding a form of pTα lacking the intracellular domain. Although surface expression of the mutant receptor was normal, our results indicate that the cytoplasmic domain of pTα is required for efficient differentiation of thymocytes and acts to costimulate the preTCR signal. These findings provide impetus for identifying proteins associated with the cytoplasmic tail that facilitate preTCR signal transduction.
Because studies using a number of species had identified Notch as a mediator of cell fate decisions, we investigated the role of this receptor and transcription factor in T cell development. Over the last few years our lab has generated several conditional mutant mice to inhibit Notch signaling in targeted tissues. We found that development of MHC2-selected CD4 T cells was inefficient to severely compromised when Notch signaling was ablated in immature thymocytes. Diminished CD4 T-cell production correlated with impaired TCR signal transduction in developing thymocytes that could be rescued with a constitutively activated form of Notch. The demonstration that TCR and Notch were functionally linked in the selection and maturation of thymocytes suggested that Notch may also regulate TCR signaling at other stages of T-cell development. We generated mice with Notch signaling-deficient peripheral T cells in order to study antigen-specific responses in T-cell activation and T-helper differentiation. We also used these mice to examine T-helper responses triggered by parasites and worms. In a reciprocal approach, we have altered expression of Notch ligand in antigen-presenting cells to assess its role in T-cell activation and the production of cytokines. Since Notch and its ligands are already potential targets for therapeutic intervention in diseases like Alzheimer’s, we need to understand how this signaling pathway operates in the immune system. Notably, our recent studies indicate that Notch function can be manipulated to enhance or attenuate immune responses.
Because of the functional connections we observed between Notch and TCR signaling in the thymus, a primary aim of the lab has been to identify downstream mediators linking these two signaling pathways. Notch is reported to directly regulate GATA3 expression, and Notch and GATA3 both impact CD4 T-cell maturation. These results prompted us to investigate whether Notch and GATA3 are jointly or coordinately involved in regulating TCR signaling in thymocyte selection. Previous attempts to find any TCR-signaling defects or alteration in the CD4/CD8 cell fate decision in GATA3-deficient thymocytes led to the proposal that GATA3 acts after lineage commitment in the maturation of CD4 T cells. To the contrary, we find that GATA3 impacts TCR signal transduction in vitro as well as positive selection and the CD4/CD8 fate decision in vivo. Our current efforts are focused on investigating how GATA3 facilitates TCR signaling at multiple stages of development as well as its role in regulating key transcription factors determining CD4/CD8 T cell fate.
After receiving an M.S. from the Medical College of Virginia, VCU, for studies of Drosophila genetics, Dr. Fowlkes conducted cancer research at the National Cancer Institute and immunology research at NIAID prior to receiving her Ph.D. for studies of thymocyte differentiation at George Washington University. She joined the Laboratory of Cellular and Molecular Immunology (LCMI) in 1987, was tenured as a senior investigator in 1990, and became chief of the T Cell Development Section in 1992. In 2013, she joined the Laboratory of Immunology (LI).
Dr. Fowlkes organizes an FAES graduate immunology course and lectures in several other immunology courses at the National Institutes of Health (NIH) and at local universities. In 1999, she was appointed adjunct professor of genetics and of microbiology/immunology at the George Washington University. Dr. Fowlkes has been on the admissions board for the NIH-Oxford/Cambridge University Partnership Graduate Program since 2001 and is currently serving as a class dean. She served as member and chair of several American Association of Immunology (AAI) committees and the NIH Immunology Interest Group (IIG) steering committee. Dr. Fowlkes has been appointed to numerous editorial and scientific advisory boards and served as scientific editor for Immunity from 2003 to 2007. She is the recipient of a Roche Basic Science Award, NIH Merit Award, and an AAI Investigator Award for Outstanding Contributions to Immunology.
Karen Laky, Staff ScientistSharron Evans, CMB Research Support Specialist (RSS)Shaye Hagler, Postbaccalaureate IRTAMitchell McGinty, Postbaccalaureate IRTA
Wang L, Wildt KF, Zhu J, Zhang X, Feigenbaum L, Tessarollo L, Paul WE, Fowlkes BJ, Bosselut R. Distinct functions for the transcription factors GATA-3 and ThPOK during intrathymic differentiation of CD4(+) T cells. Nat Immunol. 2008 Oct;9(10):1122-30.
Laky K, Fowlkes BJ. Notch signaling in CD4 and CD8 T cell development. Curr Opin Immunol. 2008 Apr;20(2):197-202.
Laky K, Fowlkes BJ. Presenilins regulate alphabeta T cell development by modulating TCR signaling. J Exp Med. 2007 Sep 3;204(9):2115-29.
Laky K, Fleischacker C, Fowlkes BJ. TCR and Notch signaling in CD4 and CD8 T-cell development. Immunol Rev. 2006 Feb;209:274-83.
Canelles M, Park ML, Schwartz OM, Fowlkes BJ. The influence of the thymic environment on the CD4-versus-CD8 T lineage decision. Nat Immunol. 2003 Aug;4(8):756-64.
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Last Updated July 15, 2014
Last Reviewed June 30, 2014