Effects of preexisting autoimmunity on heart graft prolongation after donor-specific transfusion and anti-CD154

Antibacterial Mechanism of Shikonin Against Vibrio vulnificus and Its Healing Potential on Infected Mice with Full-Thickness Excised Skin

Shikonin has anticancer, anti-inflammatory, and wound healing activities. Vibrio vulnificus is an important marine foodborne pathogen with a high fatality rate and rapid pathogenesis that can infect humans through ingestion and wounds. In this study, the antibacterial activity and possible antibacterial mechanism of shikonin against V. vulnificus were investigated. In addition, the ability of shikonin to control V. vulnificus infection in both pathways was assessed by artificially contaminated oysters and full-thickness excised skin-infected mice. Shikonin treatment can cause abnormal cell membrane function, as evidenced by hyperpolarization of the cell membrane, significant decreased intracellular ATP concentration (p < 0.05), significant increased intracellular reactive oxygen species and malondialdehyde content (p < 0.05), decreased cell membrane integrity, and changes in cell morphology. Shikonin at 40 and 80 μg/mL reduced bacterial numbers in shikonin-contaminated oysters by 3.58 and 2.18 log colony-forming unit (CFU)/mL. Shikonin can promote wound healing in mice infected with V. vulnificus by promoting the formation of granulation tissue, hair follicles, and sebaceous glands, promoting epithelial cell regeneration and epidermal growth factor production. These findings suggest that shikonin has a strong inactivation effect on V. vulnificus and can be used in food production and wound healing to effectively control V. vulnificus and reduce the number of diseases associated with it.

Inhibition of thrombin on endothelium enhances recruitment of regulatory T cells during IRI and when combined with adoptive Treg transfer, significantly protects against acute tissue injury and prolongs allograft survival

Ischemia-reperfusion injury (IRI) amplifies T cell alloimmune responses after transplantation with thrombin playing a key pro-inflammatory role. To explore the influence of thrombin on regulatory T cell recruitment and efficacy we used a well-established model of IRI in the native murine kidney. Administration of the cytotopic thrombin inhibitor PTL060 inhibited IRI, and by skewing expression of chemokines (reducing CCL2 and CCL3 but increasing CCL17 and CCL22) increased the infiltration of M2 macrophages and Tregs. When PTL060 was combined with infusion of additional Tregs, these effects were further amplified. To test the benefits of thrombin inhibition in a transplant model, BALB/c hearts were transplanted into B6 mice with or without perfusion with PTL060 in combination with Tregs. Thrombin inhibition or Treg infusion alone led to small increments in allograft survival. However, the combined therapy led to modest graft prolongation by the same mechanisms as in renal IRI; graft survival was accompanied by increased numbers of Tregs and anti-inflammatory macrophages, and reduced expression of pro-inflammatory cytokines. While the grafts succumbed to rejection associated with the emergence of alloantibody, these data suggest that thrombin inhibition within the transplant vasculature enhances the efficacy of Treg infusion, a therapy that is currently entering the clinic to promote transplant tolerance.

Triazolopyrimidine derivative NK026680 and donor-specific transfusion induces CD4+CD25+Foxp3+ T cells and ameliorates allograft rejection in an antigen-specific manner

We have previously demonstrated the unique properties of a new triazolopyrimidine derivative, NK026680, which exerts immunosuppressive effects in rat heart transplant model and confers tolerogeneic properties on ex vivo-conditioned dendritic cells in mice. We herein demonstrate that NK026680 promotes the expansion of regulatory T cells (Tregs) with potent immunoregulatory effects when used in combination with donor-specific transfusion (DST). BALB/c (H-2^d) heart graft were transplanted into C57BL/6 (H-2^b) mice following intravenous injection of donor splenocytes (DST) and oral administration of NK026680. The NK026680 plus DST treatment markedly prolonged the survival time of the donor-graft, but not that of the 3rd party-graft (C3H; H-2^k). Treg cells in the recipient spleen on day 0 expanded when stimulated with donor-antigens in vivo and in vitro. After heart transplantation, Treg cells accumulated into the graft and increased in the spleen. NK026680 plus DST also decreased activated CD8⁺ T cells in the spleen and inhibited infiltration of CD8⁺ T cells into the graft. Depletion of CD25⁺ cells inhibited the graft prolonging effect of the NK026680 plus DST treatment. NK026680 administration together with DST induces potent immunoregulatory effects in an antigen-specific manner, likely due to the in vivo generation of donor-specific Tregs.

TLR-Induced Murine Dendritic Cell (DC) Activation Requires DC-Intrinsic Complement

Induction of proinflammatory T cell immunity is augmented by innate dendritic cell (DC) maturation commonly initiated by TLR signaling. We demonstrate that ligation of TLR3, TLR4, and TLR9 induces murine DC production of complement components and local production of the anaphylatoxin C5a. In vitro, ex vivo, and in vivo analyses show that TLR-induced DC maturation, as assessed by surface phenotype, expression profiling by gene array, and functional ability to stimulate T cell responses, requires autocrine C3a receptor and C5a receptor (C3ar1/C5ar1) signaling. Studies using bone marrow chimeric animals and Foxp3-GFP/ERT2-Cre/dTomato fate-mapping mice show that TLR-initiated DC autocrine C3ar1/C5ar1 signaling causes expansion of effector T cells and instability of regulatory T cells and contributes to T cell-dependent transplant rejection. Together, our data position immune cell-derived complement production and autocrine/paracrine C3ar1/C5ar1 signaling as crucial intermediary processes that link TLR stimulation to DC maturation and the subsequent development of effector T cell responses.

Differential Impact of Chronic Hyperglycemia on Humoral Versus Cellular Primary Alloimmunity

Diabetes is prevalent among solid organ transplant recipients and is universal among islet transplant recipients. Whereas diabetes is often considered to result in an immune-compromised state, the impact of chronic hyperglycemia on host alloimmunity is not clear. Potential immune-modifying effects of obesity, autoimmunity, or diabetogenic agents like streptozotocin may confound understanding alloimmunity in experimental models of diabetes. Therefore, we sought to determine the role of chronic hyperglycemia due to insulinopenia on alloimmunity using the nonautoimmune, spontaneously diabetic H-2^b-expressing C57BL/6 Ins2^Akita mice (Akita). Akita mice harbor a mutated Ins2 allele that dominantly suppresses insulin secretion, resulting in lifelong diabetes. We used BALB/c donors (H-2^d) to assess alloimmunization and islet transplantation outcomes in Akita recipients. Surprisingly, chronic hyperglycemia had little effect on primary T-cell reactivity after alloimmunization. Moreover, Akita mice readily rejected islet allografts, and chronic hyperglycemia had no impact on the magnitude or quality of intragraft T-cell responses. In contrast, allospecific IgM and IgG were significantly decreased in Akita mice after alloimmunization. Thus, whereas diabetes influences host immune defense, hyperglycemia itself does not cause generalized alloimmune impairment. Our data suggest that immune compromise in diabetes due to hyperglycemia may not apply to cellular rejection of transplants.

Memory CD4+ T cells are suppressed by CD8+ regulatory T cells in vitro and in vivo

BACKGROUND

Acute graft rejection mediated by alloreactive memory CD4⁺ T cells is a major obstacle to transplantation tolerance. It has been reported that CD8⁺ T regulatory cells (Tregs) have the ability to induce graft tolerance by restraining the function of activated CD4⁺ T cells, but not including memory T cells. The aim of this study is to elucidate the effect of CD8⁺ Tregs on alloreactive memory CD4⁺ T cells.

METHODS

We detected Qa-1 expression and performed proliferative assay on memory CD4⁺ T cells. All memory CD4⁺ T cells were purified from mice receiving skin allografts. We performed inhibitory and cytotoxic assays on CD8⁺ Tregs, which were isolated from a T cell vaccination mouse model, and IL-2, IL-4, IL-10 and IFN-γ levels were measured in co-culture supernatants by ELISA. To confirm CD8⁺ Tregs inhibition of memory CD4⁺ T cells in-vivo, we utilized a murine model of cardiac allograft transplantation.

RESULTS

Memory CD4⁺ T cells mediated acute allograft rejection, and CD8⁺ Tregs suppressed the proliferation of memory CD4⁺ T cells. In vitro, memory CD4⁺ T cells were inhibited and lysed by CD8⁺ Tregs. There was a positive correlation between IFN-γ levels, and cell lysis rate induced by CD8⁺ Tregs. In-vivo studies demonstrated CD8⁺ Tregs prolonged graft survival times, by inhibiting CD4⁺ memory T cells, through a Qa-1-peptide-TCR pathway.

CONCLUSIONS

CD8⁺ Tregs inhibit CD4⁺ memory T cell-mediated acute murine cardiac allograft rejection, and further prolong graft survival times. These results provide new insights into immune regulation of organ rejection.

Kinetics of Alloantigen-Specific Regulatory CD4 T Cell Development and Tissue Distribution After Donor-Specific Transfusion and Costimulatory Blockade

BACKGROUND

The influence of donor-side regulation toward recipient antigens on graft outcome is poorly understood.

METHODS

Because this influence might be due in part to the accumulation of tissue-resident memory T cells in the donor organ, we used a standard murine tolerization model (donor-specific transfusion plus CD40L blockade) to determine the kinetics of development and peripheralization of allospecific regulatory T cell in lymphoid tissues and liver, a secondary lymphoid organ used in transplantation.

RESULTS

We found that donor-specific transfusion and CD40L blockade leads to a progressive and sustained T regulatory allospecific response. The cytokines IL10, TGFβ, and IL35 all contributed to the regulatory phenomenon as determined by trans vivo delayed hypersensitivity assay. Unexpectedly, an early and transient self-specific regulatory response was found as well. Using double reporter mice (forkhead box p 3 [Foxp3]-yellow fluorescent protein, Epstein-Barr virus-induced gene 3 [Ebi3]-TdTomRed), we found an increase in Foxp3+CD25+ regulatory T (Treg) cells paralleling the regulatory response. The Ebi3+ CD4 T cells (IL35-producing) were mainly classic Treg cells (Foxp3+CD25+), whereas TGFβ+ CD4 T cells are mostly Foxp3-negative, suggesting 2 different CD4 Treg cell subsets. Liver-resident TGFβ+ CD4 T cells appeared more rapidly than Ebi3-producing T cells, whereas at later timepoints, the Ebi3 response predominated both in lymphoid tissues and liver.

CONCLUSIONS

The timing of appearance of donor organ resident Treg cell subsets should be considered in experiments testing the role of bidirectional regulation in transplant tolerance.

Role of Memory T Cells and Perspectives for Intervention in Organ Transplantation

Memory T cells are necessary for protective immunity against invading pathogens, especially under conditions of immunosuppression. However, their presence also threatens transplant survival, making transplantation a great challenge. Significant progress has been achieved in recent years in advancing our understanding of the role that memory T cells play in transplantation. This review focuses on the latest advances in our understanding of the involvement of memory T cells in graft rejection and transplant tolerance and discusses potential strategies for targeting memory T cells in order to minimize allograft rejection and optimize clinical outcomes.

Effect of Absent Immune Cell Expression of Vitamin D Receptor on Cardiac Allograft Survival in Mice

INTRODUCTION

Vitamin D (VD) has immunomodulatory properties, but whether immune cell expression of the VD receptor (VDR) impacts costimulatory blockade induced cardiac allograft survival is not known.

METHODS

To localize effects of VDR deficiency to hematopoietic cells and to avoid the metabolic consequences of systemic VDR deficiency, we produced bone marrow (BM)-chimeric mice by transplanting lethally irradiated C57BL/6 mice with congenic VDR or wild type BM. After reconstitution, we characterized baseline immune profiles and transplanted chimeras with heterotopic cardiac allografts with or without costimulatory blockade using anti-CD154 (MR1) or CTLA4Ig, the latter approved for use in human kidney transplant recipients.

RESULTS

Immune reconstitution occurred equivalently in chimeras with wild type and VDR BM. Untreated animals rejected class II disparate and fully allogeneic cardiac transplants with similar kinetics. Compared to untreated controls, treatment with either MR1 or CTLA4Ig induced significant and equivalent prolongation of graft survival in both groups of chimeric recipients. We observed no differences in induced antidonor cellular or humoral alloimmunity between groups.

CONCLUSIONS

Our findings support the conclusion that absent immune cell VDR expression (a) does not impact the strength, phenotype, or kinetics of heart transplant rejection in mice and (b) does not impact the graft-prolonging effects of costimulatory blockade including that induced by clinically used CTLA4Ig.