Lymphocyte Biology Section
Ronald N. Germain, M.D., Ph.D., Chief
Ronald N. Germain received his M.D. and Ph.D. in 1976 from Harvard University, the latter for research with B. Benacerraf. Since then, he has investigated basic T-cell immunobiology, first on the faculty of Harvard Medical School and, since 1982, in the Laboratory of Immunology at NIAID. Over the years, he and his colleagues have contributed to the understanding of MHC class II structure–function relationships, the cell biology of antigen processing, and the molecular basis of T cell recognition, especially the role of self-recognition and the organization of signaling networks involved in TCR ligand discrimination. More recently, his laboratory has extended its studies in vivo, analyzing the dynamics of immune cell and host-pathogen interactions using intravital 2-photon microscopy. They have also begun developing computational models of immune function, beginning with TCR signaling.
Description of Research Program
The Lymphocyte Biology Section (LBS) studies basic aspects of innate and adaptive immune function, with an emphasis on the biochemical mechanisms involved in discrimination between self and foreign peptide-associated MHC molecules by T cells as well as on T cell-antigen presenting cell interactions and the subsequent delivery of effector function. Experiments at the biochemical, cell, tissue, and organism level are used to build a more complete picture of both the operation of and the interface between the adaptive and innate immune systems, including the use of novel microscopic live animal imaging methods. Efforts are also underway to create computer models of immune function, especially T-cell signaling and activation. The aim of this work is to create a detailed understanding of how immune responses to foreign pathogens or self antigens are initiated and unfold, as well as to develop new tools for predicting how the immune system will respond if perturbed, for example, by a candidate vaccine.
Imaging Immune Cell Dynamics and Function
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| From L to R: Polarized T cell (cyan) associated with desmin+ / ERTR-7+ (red and green) fibroblastic reticular cell (FRC) fibers; composite image of polyclonal B cells in a lymph node follicle (blue) and the migration tracks of wild-type (red) and SAP KO (green) T cells in the follicle and germinal center; dendritic cells (green) extending (‘balloon bodies”) into the gut lumen from beneath the villus epithelial cell layer (red); and activated T cells (green) in a BCG-induced liver granuloma surrounded by intact liver sinusoids (red blood tracer) and hepatocytes (blue nuclei). View a larger version. |
The LBS has made numerous contributions to the understanding of the cell biology of antigen processing and presentation by MHC class I and especially class II molecules. It also pioneered development of monoclonal antibodies to specific peptide-MHC molecule complexes and their use for visualization of the antigen presentation.
We have now moved from these studies of MHC-peptide ligand formation to studies of the recognition of these ligands by T cells. An exciting development is the establishment of multiphoton microscopy methods for real-time, high-resolution visualization of immune-cell dynamics in situ. This new technology is being used in conjunction with more conventional molecular and cellular immunological methods to (1) describe the dynamics of innate and adaptive immune cell movement in lymphoid and non-lymphoid tissue environments and to uncover the underlying mechanisms driving and guiding this cell movement; (2) localize the sites and duration of the cell-cell interactions involved in the development of adaptive immune responses; (3) analyze how differences in these aspects of cell migration and interaction impact differentiation events and functional immunity; and (4) investigate the dynamic behavior and effector activities of innate and adaptive immune cells in non-lymphoid sites, especially in the context of infections with various microbial and parasitic agents.
Our studies have allowed us to determine how long a T cell spends in contact with an antigen-bearing dendritic cell, the role of both physical (the fibroblastic reticular cell network in lymph nodes) and chemical (chemokine) cues in controlling T cell migration in secondary lymphoid tissues, the contribution of dendritic cell-associated antigens to the activation of naïve B cells in vivo, the importance of SAP in differential attachment of T cells to antigen-presenting dendritic cells vs. B cells and in germinal center formation, the involvement of neutrophils in Leishmania infection of the skin, epithelial cell TLR control of dendritic cell extension into the gut lumen for bacterial sampling, and the interplay of myeloid and lymphoid cells within mycobacterial granulomas in the liver. Watch videos from published papers reporting these findings.
Together, these studies are beginning to create a comprehensive picture of how immune cells traffic and interact during the earliest stages of immune responses, during the initiation of adaptive immunity, and during the delivery of effector functions in peripheral tissues.
Analysis and Modeling of T Cell Ligand Discrimination and Activation Control
A second major focus of the LBS is on how antigen-receptor binding events are translated into intracellular signals regulating T-cell activation and differentiation. Previous contributions include an early description of TCR antagonists and partial agonists, the discovery that such ligands induce distinct early tyrosine phosphorylation events, and the recognition that the ‘wiring’ connecting ligand engagement of the TCR to gene activation was modified during development to support effective positive and negative selection.
Ongoing work centers on dissecting the molecular basis for antigen discrimination and developmental changes in receptor-response linkage. We have identified two novel feedback regulatory pathways that help the T cell discriminate functionally between ligands of closely related structure. Such selectivity is at the heart of physiologic self/non-self discrimination. We have also uncovered evidence for a very important role of self-recognition in responses to foreign antigen that help explain the contribution of thymic-positive selection to adaptive immunity. These data are now being expanded by identification and analysis of additional TCR-linked feedback regulatory pathways involved in the control of T-cell activation and effector responses, as well as by the development of integrated computational models of early ligand discrimination by the TCR and downstream feedback control of intracellular signaling pathways. These mechanistic studies complement higher-order imaging studies in the development of a multi-scale understanding of immune function (also see Program in Systems Immunology and Infectious Disease Modeling [PSIIM]).
Members of LBS and PSIIM
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| First row (L to R): Tony Zhang, Scott Mueller, Nick van Panhuys, Ina Ifrim, Naeha Subramanian, Nienke Vrisekoop, and Bianca von Scheidt. Second row: Hai Qi, Frank Wang, Frederick Klauschen, Marcello Chieppa, Masaru Ishii, Thorsten Prustel |
Selected Publications
For a complete listing, visit PubMed.
Watch videos showing results from these and other LBS publications.
Stoll, S., Delon, J., Brotz, T. M. and Germain, R. N.: Dynamic imaging of T cell-dendritic cell interactions in lymph nodes. Science 296: 1873-1876, 2002.
Altan-Bonnet, G., and Germain, R.N.: Modeling T cell antigen discrimination based on feedback control of digital ERK responses. PLoS Biology 3:e356, 2005.
Castellino, F., Huang, A.Y.C., Altan–Bonnet, G., Stoll, S., Scheinecker, C., and Germain, R.N.: Chemokines enhance immunity by guiding naive CD8+ T cells to sites of CD4+ T cell-dendritic interaction. Nature. 440:890-5, 2006.
Bajénoff, M., Egen, J. G., Koo, L. Y., Laugier, J. P., Brau, F., Glaichenhaus, N., and Germain, R.N. Stromal cell networks regulate lymphocyte entry, migration, and territoriality in lymph nodes. Immunity 25:989-1001, 2006.
Egen, J.G., Rothfuchs, A. G., Feng, C.G., Winter, N., Sher, A., and Germain, R.N.: Macrophage and T cell dynamics during the development and disintegration of mycobacterial granulomas. Immunity 28: 271-284, 2007.
Qi, H., Cannons, J.L., Klauschen, F., Schwartzberg, P.L., and Germain, R.N.: SAP-controlled T-B cell interactions underlie germinal centre formation. Nature, 455: 764-769, 2008.
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