Breaking T cell tolerance is arguably a critical step in the pathogenesis of SLE. Activated T cells provide help to autoantibody-secreting B cells and also infiltrate target organs. Therefore it is important to identify how, where and when such T cells are activated and how this is maintained. In fact, the latter is critical because any therapy will have to interrupt ongoing disease. Lupus-prone mice lacking B cells from birth have markedly reduced disease and much less T cell activation. This suggested that B cells are upstream in T cell activation and also that they would be good therapeutic targets. However, in lupus mice B cell depletion was difficult to achieve using standard anti-CD20 mAb and effects, particularly on T cell activation, were not striking. Similarly anti-CD20 failed to show clinical effect in SLE patients, though anti-BLyS did. These findings raise the question of what the role of B cells really was in ongoing disease, and whether, if efficient depletion were possible, would T cell activation and disease be reduced. They also suggested that other cell types such as DCs could be as or more important both for initiation and propagation. In this proposal we will use genetic approaches to target key cells and molecules-including deletion during disease rather than from birth-in order to unravel the complex interplays of disease mechanisms in vivo. To this end, we recently deleted cDC and pDC in lupus- prone MRL.Faslpr mice from birth. Surprisingly, we found little effect on T cell activation in secondary lymphoid tissue (SLT), but there were striking reductions in nephritis and skin disease, decreased proteinuria and longer survival. These data suggested that DCs might be required to activate T cells in target tissues-a novel role rather than to initiate activation, as might have been assumed. We propose a new model in DCs have non- redundant roles in tissue infiltration in lupus but that B cells are the most upstream APC in SLT. To address this model, we will first deplete both B cells and DCs during ongoing disease, rather than from birth. This will validate DCs as therapeutic targets and help resolve the controversial role of B cells. We will also distinguish the roles of cDCs from pDCs, as whether pDCs are important for SLE has not been tested experimentally. Second, to understand how B cells and DCs might be activating T cells, we will block APC function by deleting MHCII from each. Further, we will investigate the role of ICOS signals, which are linked to lupus in a number of ways, including emerging data that ICOS specifies T follicular helper (TFH) and T extrafollicular helper differentiation, cells that help autoreactive B cells. We also have exciting preliminary data that ICOSL on DCs specifically is required to promote infiltrating T cells in kidney, and that such cells express Bcl6 and thus may be re- lated to TFH. To further investigate the roles of ICOS signals, we will specifically delete ICOSL on B cells and on DCs. Together these experiments-organized around Aim 1 focusing on B cells and Aim 2 focusing on DCs-will test our model;determine if B cells/DCs or both are important as APC;validate B cells, cDCs, and pDCs as therapeutic targets;and elucidate the role of ICOS signals in the development of pathogenic T cells.

Public Health Relevance

Lupus is a prototypical autoimmune disease in which the immune system is spontaneously activated and attacks self tissues. We have found that both B lymphocytes and dendritic cells play important roles in this process, in part by activating pathogenic T lymphocytes. The purposes of this proposal are: 1) to understand how B cells and dendritic cells promote T cell activation and 2) to use this information to develop animal models that can be used to develop and refine clinical therapies. We will use novel mouse genetic models and cell-depleting reagents to accomplish these goals.

National Institute of Health (NIH)
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Hypersensitivity, Autoimmune, and Immune-mediated Diseases Study Section (HAI)
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Mancini, Marie
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University of Pittsburgh
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Teichmann, Lino L; Schenten, Dominik; Medzhitov, Ruslan et al. (2013) Signals via the adaptor MyD88 in B cells and DCs make distinct and synergistic contributions to immune activation and tissue damage in lupus. Immunity 38:528-40
Modi, Badri G; Neustadter, Jason; Binda, Elisa et al. (2012) Langerhans cells facilitate epithelial DNA damage and squamous cell carcinoma. Science 335:104-8
Teichmann, Lino L; Kashgarian, Michael; Weaver, Casey T et al. (2012) B cell-derived IL-10 does not regulate spontaneous systemic autoimmunity in MRL.Fas(lpr) mice. J Immunol 188:678-85
Ahuja, Anupama; Teichmann, Lino L; Wang, Haowei et al. (2011) An acquired defect in IgG-dependent phagocytosis explains the impairment in antibody-mediated cellular depletion in Lupus. J Immunol 187:3888-94
Taveirne, Sylvie; De Colvenaer, Veerle; Van Den Broeck, Tina et al. (2011) Langerhans cells are not required for epidermal Vgamma3 T cell homeostasis and function. J Leukoc Biol 90:61-8
Teichmann, Lino L; Ols, Michelle L; Kashgarian, Michael et al. (2010) Dendritic cells in lupus are not required for activation of T and B cells but promote their expansion, resulting in tissue damage. Immunity 33:967-78
James, Scott E; Orgun, Nural N; Tedder, Thomas F et al. (2009) Antibody-mediated B-cell depletion before adoptive immunotherapy with T cells expressing CD20-specific chimeric T-cell receptors facilitates eradication of leukemia in immunocompetent mice. Blood 114:5454-63
Igyarto, Botond Z; Jenison, Matthew C; Dudda, Jan C et al. (2009) Langerhans cells suppress contact hypersensitivity responses via cognate CD4 interaction and langerhans cell-derived IL-10. J Immunol 183:5085-93
Shlomchik, Mark J (2009) Activating systemic autoimmunity: B's, T's, and tolls. Curr Opin Immunol 21:626-33
Blair, Paul A; Chavez-Rueda, Karina A; Evans, Jamie G et al. (2009) Selective targeting of B cells with agonistic anti-CD40 is an efficacious strategy for the generation of induced regulatory T2-like B cells and for the suppression of lupus in MRL/lpr mice. J Immunol 182:3492-502

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