CCR5-mediated Recruitment of NK Cells to the Kidney Is a Critical Step for Host Defense to Systemic Candida albicans Infection

C-C chemokine receptor type 5 (CCR5) regulates the trafficking of various immune cells to sites of infection. In this study, we showed that expression of CCR5 and its ligands was rapidly increased in the kidney after systemic Candida albicans infection, and infected CCR5−/−mice exhibited increased mortality and morbidity, indicating that CCR5 contributes to an effective defense mechanism against systemic C. albicans infection. The susceptibility of CCR5−/− mice to C. albicans infection was due to impaired fungal clearance, which in turn resulted in exacerbated renal inflammation and damage. CCR5-mediated recruitment of NK cells to the kidney in response to C. albicans infection was necessary for the anti-microbial activity of neutrophils, the main fungicidal effector cells. Mechanistically, C. albicans induced expression of IL-23 by CD11c+ dendritic cells (DCs). IL-23 in turn augmented the fungicidal activity of neutrophils through GM-CSF production by NK cells. As GM-CSF potentiated production of IL-23 in response to C. albicans, a positive feedback loop formed between NK cells and DCs seemed to function as an amplification point for host defense. Taken together, our results suggest that CCR5-mediated recruitment of NK cells to the site of fungal infection is an important step that underlies innate resistance to systemic C. albicans infection.

CCR5-mediated Recruitment of NK Cells to the Kidney Is a Critical Step for Host Defense to Systemic Candida albicans Infection

C-C chemokine receptor type 5 (CCR5) regulates the trafficking of various immune cells to sites of infection. In this study, we showed that expression of CCR5 and its ligands was rapidly increased in the kidney after systemic Candida albicans infection, and infected CCR5−/−mice exhibited increased mortality and morbidity, indicating that CCR5 contributes to an effective defense mechanism against systemic C. albicans infection. The susceptibility of CCR5−/− mice to C. albicans infection was due to impaired fungal clearance, which in turn resulted in exacerbated renal inflammation and damage. CCR5-mediated recruitment of NK cells to the kidney in response to C. albicans infection was necessary for the anti-microbial activity of neutrophils, the main fungicidal effector cells. Mechanistically, C. albicans induced expression of IL-23 by CD11c+ dendritic cells (DCs). IL-23 in turn augmented the fungicidal activity of neutrophils through GM-CSF production by NK cells. As GM-CSF potentiated production of IL-23 in response to C. albicans, a positive feedback loop formed between NK cells and DCs seemed to function as an amplification point for host defense. Taken together, our results suggest that CCR5-mediated recruitment of NK cells to the site of fungal infection is an important step that underlies innate resistance to systemic C. albicans infection.

Roles of IL-33 in Resistance and Tolerance to Systemic Candida albicans Infections

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.

Involvement of Protein Kinase C-delta in Vascular Permeability in Acute Lung Injury

Pulmonary edema is a major cause of mortality due to acute lung injury (ALI). The involvement of protein kinase C-delta (PKC-delta) in ALI has been a controversial topic. Here we investigated PKC-delta function in ALI using PKC-delta knockout (KO) mice and PKC inhibitors. Our results indicated that although the ability to produce proinflammatory mediators in response to LPS injury in PKC-delta KO mice was similar to that of control mice, they showed enhanced recruitment of neutrophils to the lung and more severe pulmonary edema. PKC-delta inhibition promoted barrier dysfunction in an endothelial cell layer in vitro, and administration of a PKC-delta-specific inhibitor significantly increased steady state vascular permeability. A neutrophil transmigration assay indicated that the PKC-delta inhibition increased neutrophil transmigration through an endothelial monolayer. This suggests that PKC-delta inhibition induces structural changes in endothelial cells, allowing extravasation of proteins and neutrophils.

Is CD137 Ligand (CD137L) Signaling a Fine Tuner of Immune Responses?

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.

IL-33 Priming Enhances Peritoneal Macrophage Activity in Response to Candida albicans

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.

Integration of the Innate and Adaptive Immunity by CD137-CD137L Bidirectional Signals: Implications in Allograft Rejection / 대한이식학회지

Two-signal models are useful in explaining various types of immune responses. In particular, secondary, so-called costimulatory, signals are critically required for the process of T-cell activation, survival, differentiation, and memory formation. Early studies in rodent models showed that targeting T-cell costimulatory pathways elicits immunological tolerance, providing a basis for development of costimulatory therapeutics in allograft rejection. However, as the classic definition of T-cell costimulation continues to evolve, simple blockade of costimulatory pathways has limitations in prevention of allograft rejection. Furthermore, functions of costimulatory molecules are much more diverse than initially anticipated and beyond T cells. In this mini-review, we will discuss CD137-CD137L bidirectional signals as examples showing that two-signals can be applicable to multiple phases of immune responses.

Rhamnogalacturonan II is a Toll-like receptor 4 agonist that inhibits tumor growth by activating dendritic cell-mediated CD8+ T cells

We evaluated the effectiveness of rhamnogalacturonan II (RG-II)-stimulated bone marrow-derived dendritic cells (BMDCs) vaccination on the induction of antitumor immunity in a mouse lymphoma model using EG7-lymphoma cells expressing ovalbumin (OVA). BMDCs treated with RG-II had an activated phenotype. RG-II induced interleukin (IL)-12, IL-1beta, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) production during dendritic cell (DC) maturation. BMDCs stimulated with RG-II facilitate the proliferation of CD8+ T cells. Using BMDCs from the mice deficient in Toll-like receptors (TLRs), we revealed that RG-II activity is dependent on TLR4. RG-II showed a preventive effect of immunization with OVA-pulsed BMDCs against EG7 lymphoma. These results suggested that RG-II expedites the DC-based immune response through the TLR4 signaling pathway.

Regulation of Inflammation by Bidirectional Signaling through CD137 and Its Ligand

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.

Role of Protein Kinase C-delta in Atherosclerosis / 대한혈관외과학회지

PURPOSE: Protein kinase C (PKC) has been implicated in a wide variety of cellular processes. Although PKC-delta is implicated in cell growth inhibition, as well as in cell differentiation, apoptosis, and tumor suppression, its role in atherosclerosis remains unclear. This study aimed to identify the mechanism of PKC-delta in the development of atherosclerosis. METHODS: To induce atherosclerosis, we performed allograft transplantations on aortas in mice. At 2, 4, and 6 weeks after transplantation, grafted aortas were obtained to compare the degree of atherosclerosis between wild type and PKC-delta (-/-) aorta. Alloantibody levels in the recipient mice's blood were measured. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed to quantitatively measure chemokine and cytokine mRNA expression of the inflammation from the harvested aorta. RESULTS: Atherosclerosis was more severe in the PKC-delta (-/-) aorta than in the wild type aorta. Alloantibody levels were higher in the mice grafted with aorta from the PKC-delta (-/-) mice than in the mice grafted with aorta from the wild type mice. RT-PCR revealed higher expressions of MRP-2, MCP-1, MIP-1alpha, and IL-2 in the mice grafted with aorta from the PKC-delta (-/-) mice than the wild type mice. CONCLUSION: Aorta allograft transplantation is a useful modality for inducing atherosclerosis. PKC-delta may be a negative regulator of atherosclerosis.

Anti-CD137 mAb Deletes Both Donor CD4+ and CD8+ T Cells in Acute Graft-versus-host Disease

We previously demonstrated that in vivo engagement of CD137, a member of TNF receptor superfamily, can delete allorective CD4+ T cells through the induction of activation-induced cell death (AICD) in chronic graft-versus-host disease (cGVHD) and subsequently reverse established cGVHD. In this study, we further showed that agonistic anti-CD137 mAb was highly effective in triggering AICD of donor CD8+ T cells as well as donor CD4+ T cells in the C57BL/6-->unirradiated (C57BL/6 x DBA/2)F1 acute GVHD model. Our results suggest that strong allostimulation should facilitate AICD of both alloreactive CD4+ and CD8+ T cells induced by CD137 stimulation. Therefore, depletion of pathogenic T cells using agonistic anti-CD137 mAb combined with potent TCR stimulation may be used to block autoimmune or inflammatory diseases mediated by T cells.

Recombinant TAT-CD137 Ligand Cytoplasmic Domain Fusion Protein Induces the Production of IL-6 and TNF-alpha in Peritoneal Macrophages

BACKGROUND: The ligand for CD137 (CD137L; also called 4-1BBL) is mainly expressed on activated APCs such as dendritic cells, B cells and macrophages. Even though CD137L functions as a trigger of the CD137 signaling pathway for T cell activation and expansion, engagement of CD137L can deliver a signal leading to the production of proinflammatory cytokines in macrophages. METHODS: We generated cell-permeable TAT-CD137L cytoplasmic domain fusion protein (TAT-CD137Lct) and examined its ability to initiate the CD137L reverse signaling pathway. RESULTS: Treatment of TAT-CD137Lct induced the production of high levels of IL-6 and TNF-alpha mRNAs and proteins in peritoneal macrophages. TAT-CD137Lct increased phosphorylation of Erk, p38 MAPK and Jnk, and activated transcription factors C/EBP and CREB. However, TAT-CD137Lct did not visibly affect the degradation of the inhibitor of NF-kB (IkBalpha). We further demonstrated that JNK activation was required for TAT-CD137Lct-induced production of TNF-alpha, while activation of Erk and p38 MAPK were involved in IL-6 and TNF-alpha production. CONCLUSION: Our results suggest that TAT-CD137Lct is an effective activator for the CD137L reverse signaling pathway.

Intervention with costimulatory pathways as a therapeutic approach for graft-versus-host disease

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.

Roles of Host Nonhematopoietic Cells in Autoimmunity and Donor Cell Engraftment in Graft-versus-host Disease

BACKGROUND: Graft-versus-host disease (GVHD) is initiated when alloreactive donor T cells are primed by host APCs to undergo clonal expansion and maturation. Since there is a controversy regarding the role of nonhematopoietic cells in GVHD, we wanted to investigate the influence of MHC disparity on nonhematopoietic cells on the pathogenesis of GVHD in the MHC-haplomismatched C57BL/6 (H-2(b)) or DBA/2 (H-2(d))-->unirradiated (C57BL/6xDBA/2) F(1)(BDF(1); H-2(b/d)) murine model of acute GVHD (aGVHD) or chronic GVHD (cGVHD). METHODS: We generated (BDF(1)-->C57BL/6), (BDF(1)-->DBA/2), and (BDF(1)-->BDF(1)) chimeras and examined GVHD-related parameters and donor cell engraftment in those chimeras. RESULTS: Using this experimental system, we found that 1) severe aGVHD across MHC Ag barrier depends on the expression of nonhematopoietically rather than hematopoietically derived alloAgs for maximal GVHD manifestations; 2) host APCs were sufficient to break B cell tolerance to self molecules in cGVHD, whereas host APCs were insufficient to induce autoimmunity in aGVHD; 3) donor cell engraftment was greatly enhanced in the host with MHC-matched nonhematopoietic cells. CONCLUSION: Taken together, our results provide an insight into how MHC disparity on GVHD target organs contribute to the pathogenesis of GVHD.

CD137-CD137 Ligand Interactions in Inflammation

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.

Improved Surgical Technique for Heterotopic Aortic Transplantation in Mice

Transplant arteriosclerosis is the main limitation for long-term survival of solid organ transplant recipients. Animal models would provide invaluable tools to investigate the cellular and molecular mechanisms underlying the pathogenesis of transplant arteriosclerosis, as well as for studies with novel drugs and other reagents for the prevention of the disease. We have therefore developed a modified technique for aortic transplantation in mice. The central suture ligation of the recipient abdominal aorta allowed a simpler end-to-side anastomosis of a segment of the donor thoracic aorta into the infrarenal portion of the recipient abdominal aorta. Using this technique, the overall survival rate was 94%. We also observed typical aspects of chronic rejection of the aortic allografts not observed with isografts. Our new technique is relatively easy to perform and has a low incidence of thrombosis, thus being useful for studying various aspects of transplant arteriosclerosis.

Maintenance of CD8+T-cell anergy by CD4+CD25+ regulatory T cells in chronic graft-versus-host disease

In a murine model of systemic lupus erythematosus (SLE)-like chronic graft-versus-host disease (cGVHD), donor CD8+T cells rapidly fall into anergy to host cells, while donor CD4+T cells hyperactivate B cells and break B-cell tolerance to self-Ags in the recipient mouse. The functional recovery of donor CD8+T cells can result in the conversion of cGVHD to acute GVHD (aGVHD), indicating that donor CD8+T-cell anergy is a restriction factor in the development of cGVHD. In this report, we present evidence that donor CD4+CD25+regulatory T cells (T(reg) cells) are critical in maintaining the donor CD8+T-cell anergy and thus suppressing the development of aGVHD in mice that are naturally prone to cGVHD. Our results provide a novel insight into the role of T(reg) cells in determining cGVHD versus aGVHD.

4-1BB (CD137) signals depend upon CD28 signals in alloimmune responses

Our previous study has demonstrated that there is a significant delay of Balb/c cardiac allograft rejection in the C57BL/6 4-1BB-deficient knockout recipient. In this study, we examined the effect of combined blockade of the 4-1BB and CD28 costimulatory pathways on cardiac allograft rejection in the C57BL/6-->Balb/c model. A long-term cardiac allograft survival was induced in CD28/4-1BB- deficient mice (>100 days survival in 3 of 4 mice), which was comparable with CD28-deficient mice (>100 days survival in 2 of 5 mice; P<0.2026). There was no long-term cardiac allograft survival in either wild-type (WT) or 4-1BB-deficient mice, even though 4-1BB-deficient recipients showed a significant delay of cardiac allograft rejection than WT mice. An in vitro mixed leukocyte reaction (MLR) assay showed that 4-1BB-deficient and WT mouse T cells had a similar responsiveness to allostimulation, whereas CD28- and CD28/4-1BB-deficient mouse T cells had a defective responsiveness to allostimulation. Furthermore, 4-1BB-deficient mice showed a similar CTL but an elevated Ab response against alloantigens as compared to WT mice, and the alloimmune responses of 4-1BB-deficient mice were abrogated in the CD28-deficient background. Overall, these results indicate that the CD28 costimulatory pathway plays a major role in the alloimmune response and that 4-1BB signals are dependent upon CD28 signals.

Prevention of chronic graft-versus-host disease by stimulation with glucocorticoid-induced TNF receptor

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 chronic graft-versus-host disease (cGVHD), a lupus-like autoimmune disease. A single injection of anti-GITR monoclonal antibody (DTA-1) was effective in blocking the progression of cGVHD in the parent-into-F1 model. Treatment of DTA-1 significantly decreased levels of IgG1 anti-DNA autoantibody, inhibited glomerulonephritis, and increased survival. The DTA-1-mediated inhibition of autoantibody production correlated with deletion of B cells and could occur independently of CD4+CD25+ regulatory T cells. Our results indicate that anti-GITR monoclonal antibody may be used as a potential immunotherapeutic agent for preventing cGVHD.

Prevention of Allograft Rejection by Immune Tolerance / 대한이식학회지

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.