Now, it has been being accepted that reverse signaling through CD137 ligand (CD137L) plays an important role in vivo during hematopoiesis and in immune regulation. However, due to technical difficulty in dissecting both directional signaling events simultaneously in vivo, most biological activities caused by CD137-CD137L interactions are considered as results from signaling events of the CD137 receptor. To make the story more complex, CD137-/- and CD137L-/- mice have increased or decreased immune responses in a context-dependent manner. In this Mini review, I will try to provide a plausible explanation for how CD137L signaling is controlled during immune responses.
4-1BB Ligand* ; Animals ; Hematopoiesis ; Inflammation ; Mice

The main stream of CD137 studies has been directed to the function of CD137 in CD8+ T-cell immunity, including its anti-tumor activity, and paradoxically the immunosuppressive activity of CD137, which proves to be of a great therapeutic potential for animal models of a variety of autoimmune and inflammatory diseases. Recent studies, however, add complexes to the biology of CD137. Accumulating is evidence supporting that there exists a bidirectional signal transduction pathway for the CD137 receptor and its ligand (CD137L). CD137/CD137L interactions are involved in the network of hematopoietic and nonhematopoietic cells in addition to the well characterized antigen-presenting cell-T cell interactions. Signaling through CD137L plays a critical role in the differentiation of myeloid cells and their cellular activities, suggesting that CD137L signals trigger and sustain inflammation. The overall consequence might be that the amplified inflammation by CD137L enhances the T-cell activity together with CD137 signals by upregulating costimulatory molecules, MHC molecules, cell adhesion molecules, cytokines, and chemokines. Solving this outstanding issue is urgent and will have an important clinical implication.
4-1BB Ligand ; Biology ; Cell Adhesion Molecules ; Cell Communication ; Chemokines ; Cytokines ; Inflammation ; Models, Animal ; Myeloid Cells ; Rivers ; Signal Transduction ; T-Lymphocytes

Graft-versus-host disease (GVHD) is mediated by mature donor T cells contained in the hematopoietic stem cell graft. During the development of GVHD, signaling through a variety of costimulatory receptors plays an important role in allogeneic T cell responses. Even though delivery of costimulatory signals is a prerequisite for full activation of donor T cells in the phase of their interactions with host APCs, their involvement with GVHD might occur over multiple stages. Like many other aspects of GVHD, promise of therapeutic interventions with costimulatory pathways has been gleaned from preclinical models. In this review, I summarize some of the advances in roles of costimulatory molecules in GVHD pathophysiology and discuss preclinical approaches that warrant further exploration in the clinic, focusing on novel strategies to delete pathogenic T cells.
Animals ; Graft vs Host Disease/*immunology/metabolism/*therapy ; Hematopoietic Stem Cell Transplantation ; Humans ; T-Lymphocytes/immunology/metabolism ; Transplantation Immunology/immunology ; Transplantation, Homologous

Although the majority of research on CD137 has been directed to T cells, it is becoming clear that this molecule has distinct functions in other lineages of cells, including non-hematopoietic cells. In particular, emerging evidence suggests that the CD137-its ligand (CD137L) network involving immune cells and non-immune cells, directly or indirectly regulates inflammation in both positive and negative manners. Bidirectional signaling through both CD137 and CD137L is critical in the evolution of inflammation: 1) CD137L signaling plays an indispensible role in the activation and recruitment of neutrophils by inducing the production of proinflammatory cytokines and chemokines in hematopoietic and non-hematopoietic cells such as macrophages, endothelial cells and epithelial cells; 2) CD137 signaling in NK cells and T cells is required for their activation and can influence other cells participating in inflammation via either their production of proinflammatory cytokines or engagement of CD137L by their cell surface CD137: 3) CD137 signaling can suppress inflammation by controlling regulatory activities of dendritic cells and regulatory T cells. As recognition grows of the role of dysregulated CD137 or CD137L stimulation in inflammatory diseases, significant efforts will be needed to develop antagonists to CD137 or CD137L.
Chemokines ; Cytokines ; Dendritic Cells ; Endothelial Cells ; Inflammation ; Killer Cells, Natural ; Macrophages ; Neutrophils ; T-Lymphocytes ; T-Lymphocytes, Regulatory

The development of immunosuprressants has had a significant contribution to inhibition of acute allograft rejection. However, long-term graft survival has not been realized by immunosuppressants, probably because of their nonspecific suppression of T cell activity and nonimmune side effects. The ideal way to overcome the limitations of current immunosuppressants is to induce allograft-specific immune tolerance. Transplant immunologists are exerting their efforts in achieving transplantation tolerance using three different approaches; mixed hematopoietic chimerism, costimulatory blockade, and regulation by regulatory T cells. It is expected that transplantation tolerance will soon be established as a standard immunosuppressive regimen with little side effects in preventing and reversing allograft rejection.
Allografts* ; Chimerism ; Graft Survival ; Immune Tolerance* ; Immunosuppressive Agents ; T-Lymphocytes, Regulatory ; Transplantation Tolerance

The development of immunosuprressants has had a significant influence on inhibition of acute allograft rejection. However, long-term graft survival has not been achieved by immunosuppressants, probably because of their nonspecific suppression of T cell activity and nonimmune side effects. The ideal way to overcome the limitations of current immunosuppressants is to induce allograft-specific immune tolerance. Transplant immunologists are exerting their efforts in achieving transplantation tolerance using four different approaches; costimulatory blockade, mixed hematopoietic chimerism, T cell depletion, and regulation by regulatory T cells. It is expected that transplantation tolerance will soon be established as a standard immunosuppressive regimen with little side effects in preventing and reversing allograft rejection.
Allografts ; Chimerism ; Graft Survival ; Immune Tolerance ; Immunosuppressive Agents ; T-Lymphocytes, Regulatory ; Transplantation Tolerance*

IL-33 is a multifunctional cytokine that is released in response to a variety of intrinsic and extrinsic stimuli. The role of IL-33 in Candida albicans infections is just beginning to be revealed. This cytokine has beneficial effects on host defense against systemic C. albicans infections, and it promotes resistance mechanisms by which the immune system eliminates the invading fungal pathogens; and it also elevates host tolerance by reducing the inflammatory response and thereby, potentially, tissue damage. Thus, IL-33 is classified as a cytokine that has evolved functionally to protect the host from damage by pathogens and immunopathology.
Candida albicans* ; Candida* ; Immune System ; Interleukin-33*

GITR (glucocorticoid-induced TNF receptor) is a recently identified member of the TNF receptor superfamily. The receptor is preferentially expressed on CD4+CD25+ regulatory T cells and GITR signals break the suppressive activity of the subset. In this study, we wanted to reveal the in vivo function of GITR in herpes simplex virus type 1 (HSV-1) infection. A single injection of anti-GITR mAb (DTA-1) immediately after viral infection significantly increased the number of CD4+ and CD8+ T cells expressing CD25, an activation surface marker, and secreting IFN-gamma. We confirmed these in vivo observations by showing ex vivo that re-stimulation of CD4+ or CD8+ T cells with a CD4+ or CD8+ T-cell-specific HSV-1 peptide, respectively, induced a significant elevation in cell proliferation and in IFN-gamma secretion. Our results indicate that GITR signals play a critical role in the T-cell immunity to HSV-1.
Animals ; Antibodies, Monoclonal/pharmacology ; CD4-Positive T-Lymphocytes/immunology ; CD8-Positive T-Lymphocytes/immunology ; Cell Proliferation ; Female ; Glucocorticoids/*pharmacology ; Herpes Simplex/*immunology ; Herpesvirus 1, Human/pathogenicity ; *Immunity, Cellular ; Interferon Type II/secretion ; *Lymphocyte Activation ; Mice ; Mice, Inbred BALB C ; Peptide Fragments/metabolism ; Receptors, Interleukin-2/metabolism ; Receptors, Nerve Growth Factor/genetics/immunology/*metabolism ; Receptors, Tumor Necrosis Factor/genetics/immunology/*metabolism ; Research Support, Non-U.S. Gov't ; T-Lymphocytes/*immunology/metabolism/virology

IL-33 is a member of the IL-1 cytokine family and plays a role in the host defense against bacteria, viruses, and fungi. In this study, we investigated the function of IL-33 and its receptor in in vitro macrophage responses to Candida albicans. Our results demonstrate that pre-sensitization of isolated peritoneal macrophages with IL-33 enhanced their pro-inflammatory cytokine production and phagocytic activity in response to C. albicans. These macrophage activities were entirely dependent on the ST2-MyD88 signaling pathway. In addition, pre-sensitization with IL-33 also increased ROS production and the subsequent killing ability of macrophages following C. albicans challenge. These results indicate that IL-33 may increase anti-fungal activity against Candida through macrophage-mediated resistance mechanisms.
Bacteria ; Candida ; Candida albicans* ; Fungi ; Homicide ; Humans ; Interleukin-1 ; Macrophages ; Macrophages, Peritoneal* ; Phagocytosis

Current therapies for autoimmune diseases are not cures but merely palliatives, aimed at reducing symptoms. For the most part, these treatments provide nonspecific suppression of the immune system and thus do not distinguish between a pathogenic autoimmune response and a protective immune response. Recently emerging evidence not only has indicated the involvement of members of the TNF receptor/ligand superfamilies but also has revealed exciting innovative strategies for the treatment of autoimmune diseases and other chronic inflammatory diseases without depressing the immune response in general. In this review, we will discuss the regulatory mechanisms of TNF receptor/ligand family members, such as HVEM/ LIGHT, 4-1BB/4-1BBL, and GITR/GITRL that regulate T and B cell functions and participate in the process of inflammatory diseases. We will also discuss how intervening in the costimulatory pathways mediated by these molecules might have some potential as a therapeutic approach to immune disorders.
Animals ; Apoptosis ; Autoimmune Diseases/immunology/metabolism/pathology ; B-Lymphocytes/immunology/physiology ; Dendritic Cells/physiology ; Human ; Inflammation/*immunology ; Lymphocyte Activation/immunology ; Models, Biological ; Receptors, Tumor Necrosis Factor/*physiology ; T-Lymphocytes/immunology/physiology ; Tumor Necrosis Factor/immunology/*physiology