Noninvasive and quantitative measurement of C4d deposition for the diagnosis of antibody-mediated cardiac allograft rejection

Preventative effect of TSPO ligands on mixed antibody-mediated rejection through a Mitochondria-mediated metabolic disorder

BACKGROUND

Immune-mediated rejection was the major cause of graft dysfunction. Although the advances in immunosuppressive agents have markedly reduced the incidence of T-cell-mediated rejection after transplantation. However, the incidence of antibody-mediated rejection (AMR) remains high. Donor-specific antibodies (DSAs) were considered the major mediators of allograft loss. Previously, we showed that treatment with 18-kDa translocator protein (TSPO) ligands inhibited the differentiation and effector functions of T cells and reduced the rejection observed after allogeneic skin transplantation in mice. This study we further investigate the effect of TSPO ligands on B cells and DSAs production in the recipients of mixed-AMR model.

METHODS

In vitro, we explored the effect of treatment with TSPO ligands on the activation, proliferation, and antibody production of B cells. Further, we established a heart-transplantation mixed-AMR model in rats. This model was treated with the TSPO ligands, FGIN1-27 or Ro5-4864, to investigate the role of ligands in preventing transplant rejection and DSAs production in vivo. As TSPO was the mitochondrial membrane transporters, we then investigated the TSPO ligands effect on mitochondrial-related metabolic ability of B cells as well as expression of downstream proteins.

RESULTS

In vitro studies, treatment with TSPO ligands inhibited the differentiation of B cells into CD138⁺CD27⁺ plasma cells; reduced antibodies, IgG and IgM, secretion of B cells; and suppressed the B cell activation and proliferation. In the mixed-AMR rat model, treatment with FGIN1-27 or Ro5-4864 attenuated DSA-mediated cardiac-allograft injury, prolonged graft survival, and reduced the numbers of B cells, including IgG⁺ secreting B cells, T cells and macrophages infiltrating in grafts. For the further mechanism exploration, treatment with TSPO ligands inhibited the metabolic ability of B cells by downregulating expression of pyruvate dehydrogenase kinase 1 and proteins in complexes I, II, and IV of the electron transport chain.

CONCLUSIONS

We clarified the mechanism of action of TSPO ligands on B-cell functions and provided new ideas and drug targets for the clinical treatment of postoperative AMR.

Blockade of IL-6/IL-6R Signaling Attenuates Acute Antibody-Mediated Rejection in a Mouse Cardiac Transplantation Model

Acute antibody-mediated rejection (AAMR) is an important cause of cardiac allograft dysfunction, and more effective strategies need to be explored to improve allograft prognosis. Interleukin (IL)-6/IL-6R signaling plays a key role in the activation of immune cells including B cells, T cells and macrophages, which participate in the progression of AAMR. In this study, we investigated the effect of IL-6/IL-6R signaling blockade on the prevention of AAMR in a mouse model. We established a mouse model of AAMR for cardiac transplantation via presensitization of skin grafts and addition of cyclosporin A, and sequentially analyzed its features. Tocilizumab, anti-IL-6R antibody, and recipient IL-6 knockout were used to block IL-6/IL-6R signaling. We demonstrated that blockade of IL-6/IL-6R signaling significantly attenuated allograft injury and improved survival. Further mechanistic research revealed that signaling blockade decreased B cells in circulation, spleens, and allografts, thus inhibiting donor-specific antibody production and complement activation. Moreover, macrophage, T cell, and pro-inflammatory cytokine infiltration in allografts was also reduced. Collectively, we provided a highly practical mouse model of AAMR and demonstrated that blockade of IL-6/IL-6R signaling markedly alleviated AAMR, which is expected to provide a superior option for the treatment of AAMR in clinic.

Artemisinin Attenuates Transplant Rejection by Inhibiting Multiple Lymphocytes and Prolongs Cardiac Allograft Survival

Immunological rejection is an important factor resulting in allograft dysfunction, and more valid therapeutic methods need to be explored to improve allograft outcomes. Many researches have indicated that artemisinin and its derivative exhibits immunosuppressive functions, apart from serving as a traditional anti-malarial drug. In this assay, we further explored the therapeutic effects of artemisinin for transplant rejection in a rat cardiac transplantation model. We found that it markedly attenuated allograft rejection and histological injury and significantly prolonged the survival of allograft. Upon further exploring the mechanism, we demonstrated that artemisinin not only attenuated T cell-mediated rejection (TCMR) by reducing effector T cell infiltration and inflammatory cytokine secretion and increasing regulatory T cell infiltration and immunoregulatory cytokine levels, but also attenuated antibody-mediated rejection (ABMR) through inhibition of B cells activation and antibody production. Furthermore, artemisinin also reduced macrophage infiltration in allografts, which was determined to be important for TCMR and ABMR. Moreover, we demonstrated that artemisinin significantly inhibited the function of pure T cells, B cells, and macrophages in vitro. All in all, this study provide evidence that artemisinin significantly attenuates TCMR and ABMR by targeting multiple effectors. Therefore, this agent might have potential for use in clinical settings to protect against transplant rejection.

Antibody-mediated complement activation in pathology and protection

Antibody-dependent complement activity is associated not only with autoimmune morbidity, but also with antitumor efficacy. In infectious disease, both recombinant monoclonal antibodies and polyclonal antibodies generated in natural adaptive responses can mediate complement activity to protective, therapeutic or disease-enhancing effect. Recent advances have contributed to the structural resolution of molecular complexes involved in antibody-mediated complement activation, defining the avid nature of participating interactions and pointing to how antibody isotype, subclass, hinge flexibility, glycosylation state, amino acid sequence and the contextual nature of the cognate antigen/epitope are all factors that can determine complement activity through impact on antibody multimerization and subsequent recruitment of complement component 1q. Beyond the efficiency of activation, complement activation products interact with various cell types that mediate immune adherence, trafficking, immune education and innate functions. Similarly, depending on the anatomical location and extent of activation, complement can support homeostatic restoration or be leveraged by pathogens or neoplasms to enhance infection or promote tumorigenic microenvironments, respectively. Advances in means to suppress complement activation by intravenous immunoglobulin (IVIG), IVIG mimetics and complement-intervening antibodies represent proven and promising exploratory therapeutic strategies, while antibody engineering has likewise offered frameworks to enhance, eliminate or isolate complement activation to interrogate in vivo mechanisms of action. Such strategies promise to support the optimization of antibody-based drugs that are able to tackle emerging and difficult-to-treat diseases by improving our understanding of the synergistic and antagonistic relationships between antibody mechanisms mediated by Fc receptors, direct binding and the products of complement activation.

Precise treatment of acute antibody-mediated cardiac allograft rejection in rats using C4d-targeted microbubbles loaded with nitric oxide

BACKGROUND

Antibody-mediated rejection (AMR) constitutes an important cause of cardiac allograft loss; however, all current therapeutic strategies represent systemic applications with unsatisfactory efficacy. Previously, we successfully non-invasively detected C4d, a specific marker for AMR diagnosis, in allografts using C4d-targeted microbubbles (MB_C4d). In this study, we extended this approach by incorporating nitric oxide (NO), as high NO levels manifest immunosuppressive and anti-thrombotic effects.

METHODS

We designed novel MB_C4d loaded with NO (NO-MB_C4d). A rat model of AMR was established by pre-sensitization with skin transplantation. Contrast-enhanced ultrasound (CEUS) images were obtained and quantitatively analyzed following NO-MB_C4d injection. Allograft survival and histologic features were analyzed to evaluate the therapeutic effect and underlying mechanism of NO-MB_C4d toward AMR.

RESULTS

We successfully obtained CEUS images following NO-MB_C4d injection and demonstrated that the ultrasound signal intensity of the myocardial area and clearance time of NO-MB_C4d both increased with increased C4d grade, thereby realizing non-invasive diagnosis of AMR. Furthermore, allograft survival was significantly prolonged, and rejection was obviously attenuated following NO-MB_C4d injection through significant suppression of thrombosis and reduction of inflammatory cell infiltrates. Overall, the therapeutic efficacy was significantly improved in the NO-MB_C4d group compared with the control NO-MB group, demonstrating that precise treatment could significantly improve the therapeutic efficacy compared with that afforded by systemic applications.

CONCLUSIONS

This study presented a novel tool to provide simultaneous non-invasive diagnosis and precise treatment of AMR using NO-MB_C4d CEUS imaging, which may be expected to provide a better option for recipients with AMR in clinic.

Prediction of renal allograft chronic rejection using a model based on contrast-enhanced ultrasonography

Objective

To evaluate the application of contrast‐enhanced ultrasonography (CEUS) for the diagnosis of renal allograft chronic rejection (CR).

Methods

A total of 104 patients who were suspected to have AR or CR were enrolled in this study (derivation group, n = 66; validation group, n = 38). Before biopsy, all patients received an ultrasound examination.

Results

In the CR group, rising time (RT) and time to peak (TTP) of medulla (RTm and TTPm, respectively) were significantly longer compared to those in the AR group. The kidney volume was significantly decreased in the CR group but was increased in the AR group. In the derivation group, age, change in kidney volume, and TTPm were identified as independent predictors by multivariate analysis. Based on the multivariate analysis results and area under receiver operating characteristic (ROC) curves (AUROCs) of individual markers, we constructed a new index as follows: P = −5.424 + 0.074 × age −9.818 × kidney volume change + 0.115 × TTPm; New Index = e^P/(1 + e^P). The new index discriminates CR from AR and had better AUROCs than any other parameters.

Conclusion

In conclusion, the new index provides a new diagnosis model for CR.

Rituximab prevents and reverses cardiac remodeling by depressing B cell function in mice

B lymphocytes have been shown to contribute to autoimmune diseases via producing antibodies and proinflammatory cytokines. Depletion of B cells by blocking CD20 can inhibit these diseases. Here we examined whether an antibody against CD20, rituximab (RTX) (Rituxan^@), used clinically in oncology could have similar anti-inflammatory effects in cardiac remodeling and heart failure (HF) in mice. Cardiac remodeling was established by pressure overload induced by transverse aortic constriction (TAC). Wild-type (WT) male C57BL/6 J mice were subjected to pressure overload by using transverse aortic constriction and then received RTX for 4 weeks. Administration of RTX markedly improves in vivo heart function, and suppressed heart chamber dilation, myocyte hypertrophy, fibrosis and oxidative stress in mice after TAC operation. RTX treatment also reversed established hypertrophic remodeling induced by TAC. Moreover, TAC-induced activation of multiple signaling pathways including calcineurin A, ERK1/2, STAT3, TGFβ/Smad2/3 and IKKα/β/NF-kB were remarkably attenuated in RTX-treated hearts compared with controls. These inhibitory effects of RTX were associated with inhibition of proinflammatory cytokine expression and Th2 cytokine-mediated IgG production from B cells. In conclusion, this study identifies that administration of RTX can inhibit pressure overload-induced cardiac remodeling and dysfunction in mice, and suggest that RTX may be a promising drug for treating hypertrophic disease.