Collagen type II-induced arthritis is a CD4(+) T-cell-dependent chronic inflammation in susceptible DBA/1 mice and represents an animal model of human rheumatoid arthritis. We found that development of this condition, and even established disease, are inhibited by an agonistic anti-4-1BB monoclonal antibody. Anti-4-1BB suppressed serum antibodies to collagen type II and CD4(+) T-cell recall responses to collagen type II. Crosslinking of 4-1BB evoked an antigen-specific, active suppression mechanism that differed from the results of blocking the interaction between 4-1BB and its ligand, 4-1BBL. Anti-4-1BB monoclonal antibodies induced massive, antigen-dependent clonal expansion of CD11c(+)CD8(+) T cells and accumulation of indoleamine 2,3-dioxygenase in CD11b(+) monocytes and CD11c(+) dendritic cells. Both anti-interferon-gamma and 1-methyltryptophan, a pharmacological inhibitor of indoleamine 2,3-dioxygenase, reversed the anti-4-1BB effect. We conclude that the suppression of collagen-induced arthritis was caused by an expansion of new CD11c(+)CD8(+) T cells, and that interferon-gamma produced by these cells suppresses antigen-specific CD4(+) T cells through an indoleamine 2,3-dioxygenase-dependent mechanism.

The 4-1BB (a TNFR superfamily member) is an inducible costimulatory molecule that can exert regulatory effects on T cells independently of CD28 stimulation. The in vitro expression of 4-1BB (CD137) is induced following activation of T cells with various stimuli, including anti-TCR mAbs, lectins, and a combination of PMA and ionomycin. To delineate further the physiological role of 4-1BB in immunity, mice deficient in this receptor were generated. These mutant mice developed normally, and were viable and fertile. Humoral responses to vesicular stomatitis virus were comparable with those seen in wild-type mice, whereas the IgG2a and IgG3 isotype responses to keyhole limpet hemocyanin were somewhat reduced in the mutant mice. The 4-1BB-deficient mice demonstrated enhanced T cell proliferation in response to mitogens or anti-CD3 even in the environment of reduced ability to secrete growth-supporting cytokines (IL-2 and IL-4). Although T cells from 4-1BB-deficient mice showed enhanced proliferation, the T cell immune responses of these animals, such as cytokine production and CTL activity, were diminished. In addition, 4-1BB deletion appears to play a role in the regulation of myeloid progenitor cell growth, leading to an increase in these precursor cells in peripheral blood, bone marrow, and spleen.

Suppression of an excessive systemic inflammatory response is a promising and potent strategy for treating endotoxic sepsis. Indoleamine 2,3-dioxygenase (IDO), which is the rate-limiting enzyme for tryptophan catabolism, may play a critical role in various inflammatory disorders. In this study, we report a critical role for IDO in the dysregulated immune response associated with endotoxin shock. We found that IDO knockout (IDO ؊/؊ ) mice and 1-methyl-D-tryptophan-treated, endotoxin-shocked mice had decreased levels of the cytokines, TNF-␣, IL-6, and IL-12, and enhanced levels of IL-10. Blockade of IDO is thought to promote host survival in LPS-induced endotoxin shock, yet little is known about the molecular mechanisms that regulate IDO expression during endotoxin shock. In vitro and in vivo, IDO expression was increased by exogenous IL-12, but decreased by exogenous IL-10 in dendritic cells and splenic dendritic cells. Interestingly, whereas LPS-induced IL-12 levels in serum were higher than those of IL-10, the balance between serum IL-12 and IL-10 following challenge became reversed in IDO Sepsis is a systemic inflammatory response syndrome induced by microbial infection that is characterized by hemodynamic shock and multiple organ failure (1, 2). The pathogenesis of sepsis involves a progressive and dynamic expansion of a systemic inflammatory response to bacterial infection (3). Endotoxin, or LPS, is a major component of the outer membrane of Gram-negative bacteria; as such, it is an effective trigger of the inflammatory response during infection with Gram-negative bacteria. Uncontrolled activation of LPS-induced mechanisms results in sepsis. However, growing evidence supports the idea that LPS does not directly cause septic shock and tissue injury. Rather, it stimulates the production of proinflammatory cytokines, such as TNF-␣ and IL-1␤, which, in the context of massive infections associated with sepsis, can precipitate tissue injury and lethal shock (1, 4). It is a major cause of morbidity and mortality in hospitalized patients, yet effective treatment modalities remain elusive. Sepsis is associated with acute and systemic host immune responses; in the case of cell-mediated immune responses, the release of cytokines, such as TNF-␣, IL-1␤, IL-6, IL-12p70, and IFN-␥, is mechanistically involved in sepsis development (5). Immune and inflammatory systems are controlled by multiple proand anti-inflammatory cytokines, many of which are absent under normal, homeostatic conditions. However, massive bacterial infections cause the host to produce excessive amounts of proinflammatory cytokines that threaten the host's survival (6). Thus, the balance between proinflammatory and anti-inflammatory influences is likely a critical element in the mechanism of sepsis.Dendritic cells (DCs) 3 are potent APCs and provide costimulatory signals for innate and adaptive immune responses. For example, LPS promotes DC maturation and IL-12 secretion, which primes naive CD4 T cell toward a Th1 phenotype (7). In contrast, IL-10 produc...

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V-set and Ig domain-containing 4 (VSIG4, CRIg, or Z39Ig), a newly identified B7-related cosignaling molecule, is a complement receptor and a coinhibitory ligand that negatively regulates T-cell immunity. Despite its exclusive expression on liver Kupffer cells (KCs) that play key roles in liver tolerance, the physiological role of VSIG4 in liver tolerance remains undefined. Mice lacking VSIG4 had poor survival rates and severe liver pathology in a concanavalin A (ConA)-induced hepatitis (CIH) model, which could be prevented by adoptive transfer of VSIG4 1 KCs. The absence of VSIG4 rendered endogenous liver Tand natural killer T (NKT)-cells more responsive to antigen-specific stimulation and impaired tolerance induction in those cells against their cognate antigens. T-cell costimulation with VSIG4.Ig suppressed Th1-, Th2-, and Th17-type cytokine production and arrested the cell cycle at the G 0 /G 1 phase but did not induce apoptosis in vitro. VSIG4-mediated tolerance induction and cell-cycle arrest were further supported by down-regulation of G 1 phase-specific Cdk2, Cdk4, and Cdk6, and up-regulation of tolerance-inducing p27 KIP-1 in VSIG4.Ig-stimulated T-cells. Administration of soluble VSIG4.Ig to wildtype mice prevented CIH development and prolonged the survival of mice with established CIH. Conclusion: Collectively, our results suggest that VSIG4 1 KCs play a critical role in the induction and maintenance of liver T-and NKT-cell tolerance, and that modulation of the VSIG4 pathway using a VSIG4.Ig fusion protein may provide useful immunological therapies against immune-mediated liver injury including autoimmune hepatitis.

Herpetic stromal keratitis (HSK) is a chronic inflammatory process in corneal stroma that results from recurrent HSV type 1 infection. We used the murine model of HSK to demonstrate the importance of the interaction between an inducible T cell costimulatory receptor, 4-1BB, and its ligand, 4-1BB ligand (4-1BBL), in the development of this disease. In BALB/c mice, HSK ordinarily induced by infection with the RE strain of herpes was prevented by blocking 4-1BB/4-1BBL interaction, either by deleting 4-1BB (in mutant 4-1BB−/− mice) or by introducing mAbs against 4-1BBL. The majority of T cells infiltrating the infected corneas were 4-1BB+ activated effector cells that expressed cell surface markers CD44, CD25, and/or CD62L, as well as chemokine receptors CCR1, CCR2, and CCR5, and a limited number of TCR Vβ chains (Vβ8.1/8.2, Vβ8.3, Vβ10b, and Vβ5.1/5.2, in order of abundance). Analysis of cell surface phenotypes showed that the failure to develop HSK in the 4-1BB−/− mice was associated with a reduced expression of CD62L at the time of T cell migration into the corneal stroma.

The establishment of a chronic hepatitis C (CHC) infection is associated with defective HCV-specific T cell responses. Recent studies suggest that negative T cell regulators such as programmed death 1 (PD-1) contribute to the impairment of virus-specific T cell functions in chronic viral infections. However, the implication of peripheral monocytes from CHC patients in the inhibition of HCV-specific T cell responses is only partially defined. In this study, we found that B7-H1, a ligand of PD-1, was significantly up-regulated on monocytes of CHC patients. Proliferation of T cells in response to anti-CD3 antibody was directly suppressed by B7-H1+CD14+ monocytes, and this suppression was reversed by addition of antagonistic B7-H1 mAb. Furthermore, blocking of monocyte-associated B7-H1 (moB7-H1) significantly enhanced the frequency of IFN-gamma-producing, HCV-specific CD4+ and CD8+ effector T cells and the production of Th1 cytokines, such as IL-2 but not Th2 cytokines, including IL-4 and IL-10. Upon B7-H1 blockade, production of perforin was also increased in CD8+ T cells stimulated with HCV peptides. Our findings suggest that moB7-H1 inhibits HCV-specific CD4+ and CD8+ T lymphocyte proliferation and suppresses Th1 cytokine production and perforin secretion. Blockade of the B7-H1 pathway thus represents an attractive approach in the treatment of chronic HCV infection.

The co-signaling molecule B7-H1 (CD274) functions as both a co-inhibitor through programmed death-1 (PD-1) receptor and a co-stimulator via an as-yet-unidentified receptor on T cells. We investigated the physiological role of endogenous B7-H1 in the pathogenesis of herpetic stromal keratitis (HSK) caused by herpes simplex virus type 1 (HSV-1). Following HSV-1 infection of the cornea of mice, B7-H1 expression was up-regulated in the CD11b + macrophage population in the draining lymph nodes (dLN) and in the inflamed cornea. In addition, HSV-1 infection significantly increased PD-1 expression on CD4 + T cells in the dLN and inflamed cornea. The administration of antagonistic B7-H1 monoclonal antibody resulted in the proliferation of HSV-specific CD4 + T cells that secreted interferon (INF)-c, and inhibited the apoptosis of HSV-specific CD4 + T cells, which exaggerated HSK. These results strongly suggest that the B7-H1 may be involved in suppression of the development of HSK.