Faculty Bibliography

Dendritic cells (DCs) comprise distinct functional subsets including CD8(-) and CD8(+) classical DCs (cDCs) and interferon-secreting plasmacytoid DCs (pDCs). The cytokine Flt3 ligand (Flt3L) controls the development of DCs and is particularly important for the pDC and CD8(+) cDC and their CD103(+) tissue counterparts. We report that mammalian target of rapamycin (mTOR) inhibitor rapamycin impaired Flt3L-driven DC development in vitro, with the pDCs and CD8(+)-like cDCs most profoundly affected. Conversely, deletion of the phosphoinositide 3-kinase (PI3K)-mTOR negative regulator Pten facilitated Flt3L-driven DC development in culture. DC-specific Pten targeting in vivo caused the expansion of CD8(+) and CD103(+) cDC numbers, which was reversible by rapamycin. The increased CD8(+) cDC numbers caused by Pten deletion correlated with increased susceptibility to the intracellular pathogen Listeria. Thus, PI3K-mTOR signaling downstream of Flt3L controls DC development, and its restriction by Pten ensures optimal DC pool size and subset composition.

In APCs, the protein tyrosine kinase Syk is required for signaling of several immunoreceptors, including the BCR and FcR. We show that conditional ablation of the syk gene in dendritic cells (DCs) abrogates FcgammaR-mediated cross priming of diabetogenic T cells in RIP-mOVA mice, a situation phenocopied in wild-type RIP-mOVA mice treated with the selective Syk inhibitor R788. In addition to blocking FcgammaR-mediated events, R788 also blocked BCR-mediated Ag presentation, thus broadly interrupting the humoral contributions to T cell-driven autoimmunity. Indeed, oral administration of R788 significantly delayed spontaneous diabetes onset in NOD mice and successfully delayed progression of early-established diabetes even when treatment was initiated after the development of glucose intolerance. At the DC level, R788 treatment was associated with reduced insulin-specific CD8 priming and decreased DC numbers. At the B cell level, R788 reduced total B cell numbers and total Ig concentrations. Interestingly, R788 increased the number of IL-10-producing B cells, thus inducing a tolerogenic B cell population with immunomodulatory activity. Taken together, we show by genetic and pharmacologic approaches that Syk in APCs is an attractive target in T cell-mediated autoimmune diseases such as type 1 diabetes.

Plasmacytoid dendritic cells (PDC) represent a distinct immune cell type specialized in direct virus recognition and rapid secretion of type I interferon. The origin and lineage affiliation of PDC have been controversial, partly because PDC show features of both lymphocytes and dendritic cells (DC). Recent studies helped elucidate the cellular and molecular basis of PDC development. In particular, the common developmental origin and genetic similarity of PDC and classical antigen-presenting DC have been established. In addition, E protein transcription factor E2-2 was shown to control lineage commitment and gene expression program of PDC. Because E proteins are essential regulators of lymphocyte development, E2-2 activity may underlie the distinct 'lymphoid' features of PDC.

Dendritic cells (DCs) must achieve a critical balance between activation and tolerance, a process influenced by cytokines and growth factors. IL-10, which transduces signals through Stat3, has emerged as one important negative regulator of DC activation. To directly examine the role Stat3 plays in regulating DC activity, the Stat3 gene was targeted for deletion with a CD11c-cre transgene. Stat3 CKO mice developed cervical lymphadenopathy as well as a mild ileocolitis that persisted throughout life and was associated with impaired weight gain. Consistent with this, Stat3-deficient DCs demonstrated enhanced immune activity, including increased cytokine production, Ag-dependent T-cell activation and resistance to IL-10-mediated suppression. These results reveal a cell-intrinsic negative regulatory role of Stat3 in DCs and link increased DC activation with perturbed immune homeostasis and chronic mucosal inflammation.

Interleukin-15 receptor alpha (IL-15R alpha) is a pleiotropically expressed molecule that chaperones and trans-presents IL-15 to NK and T cells. To investigate whether IL-15R alpha presented by different cells perform distinct physiological functions, we have generated four lines of mice lacking IL-15R alpha in various cell types. We find that IL-15R alpha expression on macrophages but not dendritic cells (DCs) supports the early transition of antigen specific effector CD8(+) T cells to memory cells. After memory CD8(+) T cell differentiation, IL-15R alpha expression on DCs selectively supports central memory CD8(+) T cells, whereas IL-15R alpha expression on macrophages supports both central and effector memory CD8(+) T cells. By contrast, mice lacking IL-15R alpha on macrophages, DCs, or both, exhibit equivalent defects in NK cell homeostasis and activation. These studies define unique roles for macrophage expression of IL-15R alpha and show that NK cells rely upon distinct IL-15R alpha dependent IL-15 signals than memory CD8(+) T cells. Moreover, they demonstrate the diversity, specification, and geographic restriction of cytokine signals.

T follicular helper (Tfh) cells represent a recently defined CD4(+) T cell subset characterized by the expression of the chemokine receptor CXCR5 and an enhanced ability to support B cells to mount antibody responses. Here, we demonstrate that lymph-node-resident CXCR5(+) Tfh cells and gut-homing integrin alpha(4)beta(7)-expressing T helper cells are generated as separate subsets in the gut-draining mesenteric lymph nodes. Type I interferon signaling in dendritic cells and in nonhematopoietic cells selectively stimulates Tfh cell development in response to antigen in conjunction with Toll-like receptor (TLR)3 or TLR4 agonists. Consistent with this, the ability of dendritic cells to produce the cytokine IL-6, required for in vivo Tfh differentiation, and antibody affinity maturation are both reduced in absence of type I interferon signaling. Thus, our results identify type I interferon as a natural adjuvant that selectively supports the generation of lymph node resident Tfh cells.

The development, homeostasis, and function of B lymphocytes involve multiple rounds of B-cell receptor (BCR)-controlled proliferation and prolonged maintenance. We analyzed the role of transcription factor Zfx, a recently identified regulator of hematopoietic stem cell maintenance, in B-cell development and homeostasis. Panhematopoietic or B cell-specific deletion of Zfx in the bone marrow blocked B-cell development at the pre-BCR selection checkpoint. Zfx deficiency in peripheral B cells caused accelerated B-cell turnover, depletion of mature recirculating B cells, and delayed T-dependent antibody responses. In addition, the numbers and function of B-1 cell lineage were reduced. Zfx-deficient B cells showed normal proximal BCR signaling, but impaired BCR-induced proliferation and survival in vitro. This was accompanied by aberrantly enhanced and prolonged integrated stress response and by delayed induction of cyclin D2 and Bcl-xL proteins. Thus, Zfx restrains the stress response and couples antigen receptor signaling to cell expansion and maintenance during B-cell development and peripheral homeostasis. These results identify a novel transcriptional regulator of the B-cell lineage and highlight the common genetic control of stem cell maintenance and lymphocyte homeostasis.

IL-7 is a cytokine that is required for T-cell development and homeostasis as well as for lymph node organogenesis. Despite the importance of IL-7 in the immune system and its potential therapeutic relevance, questions remain regarding the sites of IL-7 synthesis, specific cell types involved and molecular mechanisms regulating IL-7 expression. To address these issues, we generated two bacterial artificial chromosome (BAC) transgenic mouse lines in which IL-7 regulatory elements drive expression of either Cre recombinase or a human CD25 (hCD25) cell surface reporter molecule. Expression of the IL-7.hCD25 BAC transgene, detected by reactivity with anti-hCD25 antibody, mimicked endogenous IL-7 expression. Fetal and adult tissues from crosses between IL-7.Cre transgenic mice and Rosa26R or R26-EYFP reporters demonstrated X-gal or YFP staining in tissues known to express endogenous IL-7 at some stage during development. These transgenic lines provide novel genetic tools to identify IL-7 producing cells in various tissues and to manipulate gene expression selectively in IL-7 expressing cells.

The swift production of type I IFNs is one of the fundamental aspects of innate immune responses against viruses. Plasmacytoid dendritic cell-derived type I IFNs are of prime importance for the initial control of highly cytopathic viruses such as the mouse hepatitis virus (MHV). The aim of this study was to determine the major target cell populations of this first wave of type I IFNs. Generation of bone marrow-chimeric mice expressing the type I IFN receptor (IFNAR) on either hemopoietic or non-bone marrow-derived cells revealed that the early control of MHV depended mainly on IFNAR expression on hemopoietic cells. To establish which cell population responds most efficiently to type I IFNs, mice conditionally deficient for the IFNAR on different leukocyte subsets were infected with MHV. This genetic analysis revealed that IFNAR expression on LysM+ macrophages and CD11c+ dendritic cells was most important for the early containment of MHV within secondary lymphoid organs and to prevent lethal liver disease. This study identifies type I IFN-mediated cross-talk between plasmacytoid dendritic cells on one side and macrophages and conventional dendritic cells on the other, as an essential cellular pathway for the control of fatal cytopathic virus infection.

Dendritic cells are critically involved in the promotion and regulation of T cell responses. Here, we report a mouse strain that lacks conventional CD11c(hi) dendritic cells (cDCs) because of constitutive cell-type specific expression of a suicide gene. As expected, cDC-less mice failed to mount effective T cell responses resulting in impaired viral clearance. In contrast, neither thymic negative selection nor T regulatory cell generation or T cell homeostasis were markedly affected. Unexpectedly, cDC-less mice developed a progressive myeloproliferative disorder characterized by prominent extramedullary hematopoiesis and increased serum amounts of the cytokine Flt3 ligand. Our data identify a critical role of cDCs in the control of steady-state hematopoiesis, revealing a feedback loop that links peripheral cDCs to myelogenesis through soluble growth factors, such as Flt3 ligand.