Amy E. Juedes

ICOS co-stimulatory receptor is essential for T-cell activation and function

T-lymphocyte activation and immune function are regulated by co-stimulatory molecules. CD28, a receptor for B7 gene products, has a chief role in initiating T-cell immune responses. CTLA4, which binds B7 with a higher affinity, is induced after T-cell activation and is involved in downregulating T-cell responses. The inducible co-stimulatory molecule (ICOS), a third member of the CD28/CTLA4 family, is expressed on activated T cells. Its ligand B7H/B7RP-1 is expressed on B cells and in non-immune tissues after injection of lipopolysaccharide into animals. To understand the role of ICOS in T-cell activation and function, we generated and analysed ICOS-deficient mice. Here we show that T-cell activation and proliferation are defective in the absence of ICOS. In addition, ICOS -/- T cells fail to produce interleukin-4 when differentiated in vitro or when primed in vivo. ICOS is required for humoral immune responses after immunization with several antigens. ICOS-/- mice showed greatly enhanced susceptibility to experimental autoimmune encephalomyelitis, indicating that ICOS has a protective role in inflammatory autoimmune diseases.

Antigen-driven effector CD8 T cell function regulated by T-bet

Type 1 immunity relies on the differentiation of two major subsets of T lymphocytes, the CD4+ T helper (Th) cell and the CD8+ cytotoxic T cell, that direct inflammatory and cytotoxic responses essential for the destruction of intracellular and extracellular pathogens. In contrast to CD4 cells, little is known about transcription factors that control the transition from the CD8 naïve to effector cell stage. Here, we report that the transcription factor T-bet, known to regulate Th cell differentiation, also controls the generation of the CD8+ cytotoxic effector cell. Antigen-driven generation of effector CD8+ cells was impaired in OT-I T cell receptor transgenic mice lacking T-bet, resulting in diminished cytotoxicity and a marked shift in cytokine secretion profiles. Furthermore, mice lacking T-bet responded poorly to infection with lymphocytic choriomeningitis virus. T-bet is a key player in the generation of type 1 immunity, in both Th and T cytotoxic cells.

Altered vascular permeability and early onset of experimental autoimmune encephalomyelitis in PECAM-1–deficient mice

Platelet/endothelial cell adhesion molecule-1 (PECAM-1, CD31), a 130-kDa glycoprotein member of the Ig superfamily of transmembrane proteins, is expressed on endothelial cells, platelets, and subsets of leukocytes. It functions as a cell adhesion molecule as well as a scaffolding molecule capable of modulating cellular signaling pathways. In this study, using PECAM-1-deficient (KO) mice, as well as cells derived from these mice, we demonstrate that the absence of PECAM-1 expression is associated with an early onset of clinical symptoms during experimental autoimmune encephalomyelitis (EAE), a mouse model for the human autoimmune disease multiple sclerosis. During EAE, mononuclear cell extravasation and infiltration of the CNS occur at earlier time points in PECAM-KO mice than in wild-type mice. In vitro, T lymphocyte transendothelial migration across PECAM-KO endothelial cells is enhanced, regardless of expression of PECAM-1 on transmigrating T cells. Additionally, cultured PECAM-KO endothelial cells exhibit prolonged permeability changes in response to histamine treatment compared with PECAM-1-reconstituted endothelial cells. Lastly, we demonstrate an exaggerated and prolonged CNS vascular permeability during the development of EAE and a delay in restoration of dermal vascular integrity following histamine challenge in PECAM-KO mice.

Kinetics and Cellular Origin of Cytokines in the Central Nervous System: Insight into Mechanisms of Myelin Oligodendrocyte Glycoprotein-Induced Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein (MOG) in C57BL/6 (H-2b) mice is characterized by early (day 12) acute paralysis, followed by a sustained chronic clinical course that gradually stabilizes. Extensive inflammation and demyelination coincide with clinical signs of disease. To identify the mechanisms of these processes, individual proinflammatory and anti-inflammatory cytokines and chemokines were studied. Sensitive single-cell assays were utilized to determine the cellular origin and kinetics of cytokine production in the CNS. Immunization with MOG35–55 peptide resulted in priming of both Th1 (lymphotoxin, IFN-γ, and TNF-α) and Th2 (IL-4) cells in the spleen. However, only Th1 cells were apparent in the CNS. CD4 T cells that produced IFN-γ or TNF-α were present in the CNS by day 7 after immunization with MOG35–55, peaked at day 20, and then waned. TNF-α was also produced in the CNS by Mac-1+ cells. On days 7 and 10 after immunization, the TNF-α-producing Mac1+ cells were predominantly microglia. By day 14, a switch occurred in that the Mac1+ TNF-α-producing cells had the phenotype of infiltrating macrophages. RANTES, IFN-inducible protein 10 (IP-10), and monocyte chemotactic protein 1 chemokine mRNA were detected in the CNS by day 8 after immunization. The early presence of monocyte chemotactic protein 1 (MCP-1) in the CNS provides a mechanism for the recruitment of macrophages. These data implicate TNF-α production by a continuum of T cells, microglia, and macrophages at various times during the course of disease. The importance of Th1 cytokines is highlighted, with little evidence for a role of Th2 cytokines.

Resident and Infiltrating Central Nervous System APCs Regulate the Emergence and Resolution of Experimental Autoimmune Encephalomyelitis

During experimental autoimmune encephalomyelitis (EAE), autoreactive Th1 T cells invade the CNS. Before performing their effector functions in the target organ, T cells must recognize Ag presented by CNS APCs. Here, we investigate the nature and activity of the cells that present Ag within the CNS during myelin oligodendrocyte glycoprotein-induced EAE, with the goal of understanding their role in regulating inflammation. Both infiltrating macrophages (Mac-1+CD45high) and resident microglia (Mac-1+CD45int) expressed MHC-II, B7-1, and B7-2. Macrophages and microglia presented exogenous and endogenous CNS Ags to T cell lines and CNS T cells, resulting in IFN-γ production. In contrast, Mac-1− cells were inefficient APCs during EAE. Late in disease, after mice had partially recovered from clinical signs of disease, there was a reduction in Ag-presenting capability that correlated with decreased MHC-II and B7-1 expression. Interestingly, although CNS APCs induced T cell cytokine production, they did not induce proliferation of either T cell lines or CNS T cells. This was attributable to production by CNS cells (mainly by macrophages) of NO. T cell proliferation was restored with an NO inhibitor, or if the APCs were obtained from inducible NO synthase-deficient mice. Thus, CNS APCs, though essential for the initiation of disease, also play a down-regulatory role. The mechanisms by which CNS APCs limit the expansion of autoreactive T cells in the target organ include their production of NO, which inhibits T cell proliferation, and their decline in Ag presentation late in disease.

T-bet controls autoaggressive CD8 lymphocyte responses in type 1 diabetes

The T-box transcription factor T-bet is known to control lineage commitment and interferon-γ production by T helper 1 (Th1) CD4 lymphocytes. We report here that T-bet is essential for development of CD8 lymphocyte-dependent autoimmune diabetes (type 1 diabetes [T1D]) in the rat insulin promoter–lymphocytic choriomeningitis virus (LCMV) transgenic model for virally induced T1D. In the absence of T-bet, autoaggressive (anti-LCMV) CD8 lymphocytes were reduced in number and produced less IFN-γ, but increased IL-2 compared with controls. Further analysis showed that T-bet intrinsically controls the generation, but not apoptosis, maintenance, or secondary expansion of antiviral effector/memory CD8 lymphocytes. This observation points toward a therapeutic opportunity for the treatment of T1D and other autoimmune disorders.

Helicobacter-Induced Chronic Active Lymphoid Aggregates Have Characteristics of Tertiary Lymphoid Tissue

ABSTRACT Susceptible strains of mice that are naturally or experimentally infected with murine intestinal helicobacter species develop hepatic inflammatory lesions that have previously been described as chronic active hepatitis. The inflammatory infiltrates in some models of chronic autoimmunity or inflammation resemble tertiary lymphoid organs hypothesized to arise by a process termed lymphoid organ neogenesis. To determine whether hepatic inflammation caused by infection with helicobacter could give rise to tertiary lymphoid organs, we used fluorescence-activated cell sorting, immunohistochemistry, and in situ hybridization techniques to identify specific components characteristic of lymphoid organs in liver tissue sections and liver cell suspensions from helicobacter-infected mice. Small venules (high endothelial venules [HEVs]) in inflammatory lesions in Helicobacter species-infected livers were positive for peripheral node addressin. Mucosal addressin cell adhesion molecule also stained HEVs and cells with a staining pattern consistent with scattered stromal cells. The chemokines SLC (CCL 21) and BLC (CXCL13) were present, as were B220-positive B cells and T cells. The latter included a naïve (CD45lo-CD62Lhi) population. These findings suggest that helicobacter-induced chronic active hepatitis arises through the process of lymphoid organ neogenesis.

Transforming Growth Factor-β Suppresses the Activation of CD8+ T-Cells When Naïve but Promotes Their Survival and Function Once Antigen Experienced : A Two-Faced Impact on Autoimmunity

OBJECTIVE—Transforming growth factor-β (TGF-β) can exhibit strong immune suppression but has also been shown to promote T-cell growth. We investigated the differential effect of this cytokine on CD8+ T-cells in autoimmunity and antiviral immunity. RESEARCH DESIGN AND METHODS—We used mouse models for virally induced type 1 diabetes in conjunction with transgenic systems enabling manipulation of TGF-β expression or signaling in vivo. RESULTS—Surprisingly, when expressed selectively in the pancreas, TGF-β reduced apoptosis of differentiated autoreactive CD8+ T-cells, favoring their expansion and infiltration of the islets. These results pointed to drastically opposite roles of TGF-β on naïve compared with antigen-experienced/memory CD8+ T-cells. Indeed, in the absence of functional TGF-β signaling in T-cells, fast-onset type 1 diabetes caused by activation of naïve CD8+ T-cells occurred faster, whereas slow-onset disease depending on accumulation and activation of antigen-experienced/memory CD8+ T-cells was decreased. TGF-β receptor–deficient CD8+ T-cells showed enhanced activation and expansion after lymphocytic choriomeningitis virus infection in vivo but were more prone to apoptosis once antigen experienced and failed to survive as functional memory cells. In vitro, TGF-β suppressed naïve CD8+ T-cell activation and γ-interferon production, whereas memory CD8+ T-cells stimulated in the presence of TGF-β showed enhanced survival and increased production of interleukin-17 in conjunction with γ-interferon. CONCLUSIONS—The effect of TGF-β on CD8+ T-cells is dependent on their differentiation status and activation history. These results highlight a novel aspect of the pleiotropic nature of TGF-β and have implications for the design of immune therapies involving this cytokine.

TGF-β suppresses the activation of CD8+ T cells when naïve but promotes their survival and function once antigen-experienced: a two-faced impact on autoimmunity

OBJECTIVE—Transforming growth factor-β (TGF-β) can exhibit strong immune suppression but has also been shown to promote T-cell growth. We investigated the differential effect of this cytokine on CD8+ T-cells in autoimmunity and antiviral immunity. RESEARCH DESIGN AND METHODS—We used mouse models for virally induced type 1 diabetes in conjunction with transgenic systems enabling manipulation of TGF-β expression or signaling in vivo. RESULTS—Surprisingly, when expressed selectively in the pancreas, TGF-β reduced apoptosis of differentiated autoreactive CD8+ T-cells, favoring their expansion and infiltration of the islets. These results pointed to drastically opposite roles of TGF-β on naïve compared with antigen-experienced/memory CD8+ T-cells. Indeed, in the absence of functional TGF-β signaling in T-cells, fast-onset type 1 diabetes caused by activation of naïve CD8+ T-cells occurred faster, whereas slow-onset disease depending on accumulation and activation of antigen-experienced/memory CD8+ T-cells was decreased. TGF-β receptor–deficient CD8+ T-cells showed enhanced activation and expansion after lymphocytic choriomeningitis virus infection in vivo but were more prone to apoptosis once antigen experienced and failed to survive as functional memory cells. In vitro, TGF-β suppressed naïve CD8+ T-cell activation and γ-interferon production, whereas memory CD8+ T-cells stimulated in the presence of TGF-β showed enhanced survival and increased production of interleukin-17 in conjunction with γ-interferon. CONCLUSIONS—The effect of TGF-β on CD8+ T-cells is dependent on their differentiation status and activation history. These results highlight a novel aspect of the pleiotropic nature of TGF-β and have implications for the design of immune therapies involving this cytokine.

Increased Memory Conversion of Naïve CD8 T Cells Activated during Late Phases of Acute Virus Infection Due to Decreased Cumulative Antigen Exposure

Background Memory CD8 T cells form an essential part of protective immunity against viral infections. Antigenic load, costimulation, CD4-help, cytokines and chemokines fluctuate during the course of an antiviral immune response thus affecting CD8 T cell activation and memory conversion. Methodology/Principal Findings In the present study, naïve TCR transgenic LCMV-specific P14 CD8 T cells engaged at a late stage during the acute antiviral LCMV response showed reduced expansion kinetics but greater memory conversion in the spleen. Such late activated cells displayed a memory precursor effector phenotype already at the peak of the systemic antiviral response, suggesting that the environment determined their fate during antigen encounter. In the spleen, the majority of late transferred cells exhibited a central memory phenotype compared to the effector memory displayed by the early transferred cells. Increasing the inflammatory response by exogenous administration of IFNγ, PolyI:C or CpG did not affect memory conversion in the late transferred group, suggesting that the diverging antigen load early versus later during acute infection had determined their fate. In agreement, reduction in the LCMV antigenic load after ribavirin treatment enhanced the contribution of early transferred cells to the long lasting memory pool. Conclusions/Significance Our results show that naïve CD8 cells, exposed to reduced duration or concentration of antigen during viral infection convert into memory more efficiently, an observation that could have significant implications for vaccine design.