Allorecognition

Adaptive immune disorders in hypertension and heart failure: focusing on T-cell subset activation and clinical implications

: Hypertension is a growing health concern worldwide. Established hypertension is a causative factor of heart failure, which is characterized by increased vascular resistance and intractable uncontrolled blood pressure. Hypertension and heart failure have multiple causes and complex pathophysiology but cellular immunity is thought to contribute to the development of both. Recent studies showed that T cells play critical roles in hypertension and heart failure in humans and animals, with various stimuli leading to the formation of effector T cells that infiltrate the cardiovascular wall. Monocytes/macrophages also accumulate in the cardiovascular wall. Various cytokines (e.g. interleukin-6, interleukin-17, interleukin-10, tumor necrosis factor-α, and interferon-γ) released from immune cells of various subtypes promote vascular senescence and elastic laminal degradation as well as cardiac fibrosis and/or hypertrophy, leading to cardiovascular structural alterations and dysfunction. Recent laboratory evidence has defined a link between inflammation and the immune system in initiation and progression of hypertension and heart failure. Moreover, cross-talk among natural killer cells, adaptive immune cells (T cells and B cells), and innate immune cells (i.e. monocytes, macrophages, neutrophils, and dendritic cells) contributes to end-cardiovasculature damage and dysfunction in hypertension and heart failure. Clinical and experimental studies on the diagnostic potential of T-cell subsets revealed that blood regulatory T cells, CD4 cells, CD8 T cells, and the ratio of CD4 to CD8 T cells show promise as biomarkers of hypertension and heart failure. Therapeutic interventions to suppress activation of these cells may prove beneficial in reducing end-organ damage and preventing consequences of cardiovascular failure, including hypertension of heart failure.

Modeling rejection immunity

Background

Transplantation is often the only way to treat a number of diseases leading to organ failure. To overcome rejection towards the transplanted organ (graft), immunosuppression therapies are used, which have considerable side-effects and expose patients to opportunistic infections. The development of a model to complement the physician’s experience in specifying therapeutic regimens is therefore desirable. The present work proposes an Ordinary Differential Equations model accounting for immune cell proliferation in response to the sudden entry of graft antigens, through different activation mechanisms. The model considers the effect of a single immunosuppressive medication (e.g. cyclosporine), subject to first-order linear kinetics and acting by modifying, in a saturable concentration-dependent fashion, the proliferation coefficient. The latter has been determined experimentally. All other model parameter values have been set so as to reproduce reported state variable time-courses, and to maintain consistency with one another and with the experimentally derived proliferation coefficient.

Results

The proposed model substantially simplifies the chain of events potentially leading to organ rejection. It is however able to simulate quantitatively the time course of graft-related antigen and competent immunoreactive cell populations, showing the long-term alternative outcomes of rejection, tolerance or tolerance at a reduced functional tissue mass. In particular, the model shows that it may be difficult to attain tolerance at full tissue mass with acceptably low doses of a single immunosuppressant, in accord with clinical experience.

Conclusions

The introduced model is mathematically consistent with known physiology and can reproduce variations in immune status and allograft survival after transplantation. The model can be adapted to represent different therapeutic schemes and may offer useful indications for the optimization of therapy protocols in the transplanted patient.

Direct microbicidal activity of cytotoxic T-lymphocytes

Cytotoxic T-lymphocytes (CTL) are famous for their ability to kill tumor, allogeneic and virus-infected cells. However, an emerging literature has now demonstrated that CTL also possess the ability to directly recognize and kill bacteria, parasites, and fungi. Here, we review past and recent findings demonstrating the direct microbicidal activity of both CD4⁺ and CD8⁺ CTL against various microbial pathogens. Further, this review will outline what is known regarding the mechanisms of direct killing and their underlying signalling pathways.

Tracking the rejection and survival of mouse ovarian iso- and allografts in vivo with bioluminescent imaging

The applications of in vivo bioluminescent imaging (BLI) with a luciferase reporter gene occur widely across biomedical fields. Luciferase-transgenic mice are highly useful donors for tracking transplanted ovarian tissues. Realizing the full potential of this system may greatly benefit the study of the physiological behaviour and function of transplanted grafts, and the rapid and reliable evaluation of new transplantation protocols. The ovarian tissues of donor FVB/N-Tg(PolII-Luc)Ltc transgenic mice, with a luciferase transgene as the reporter, were transplanted into iso/allogeneic recipients. Rejection, ovarian function and BLI were quantitatively analysed in vivo over time. The BLI of the ovarian isografts revealed longer survival than that of allografts, even with cyclosporine A (CsA) treatment. The CD4(+)/CD8(+) ratios of peripheral T-cells were significantly reduced in allografts compared with those in isografts (P<0.0001) during rejection, whereas CD19(+) cell numbers were higher in allografts. The infiltration of CD4(+)/CD8(+) cells into the graft was unremarkable in isografts from day 1, but was strong in allografts from day 8 onwards. Hormone activity revealed complete oestrus cycles in the isografts but only the dioestrus stage in the allografts. These results demonstrate that BLI in vivo expedites the fast throughput and fate maps of ovarian grafts. The use of BLI to longitudinally monitor ovarian grafts for immunorejection demonstrated the short survival of allografts and the much longer survival of isografts. CsA treatment alone is ineffective against the acute rejection of ovarian allografts.

Regulatory T cells after organ transplantation: where does their action take place?

Regulatory T cells are considered to be pivotal for the induction of tolerance to donor antigens. In the past decades, several regulatory T-cell subsets have been identified, such as CD4(+)CD25(+) regulatory T cells and the CD8(+)CD28(-) suppressor T cells. Although many studies have investigated the role of these regulators in transplant tolerance, relatively little attention has focused on the exact place where these cells suppress immune responses directed to donor antigens. The localization of regulatory T cells may influence their effect on allogeneic immune responses. More insight into the localization and migration of regulatory T cells in transplant recipients is therefore important, especially when these cells are to be used for monitoring purposes and for cellular immune therapy. In the present review we summarize current knowledge about the presence of functional donor-directed regulatory T cells in the secondary lymphoid organs, peripheral blood, and the transplanted organ itself. In addition, we discuss the importance of the appropriate localization for the control of anti-donor immune reactivity.

Assays for alloreactive responses by PCR

In organ transplantation, major efforts are currently developed to minimize or even to withdraw immunosuppressive drugs. Different protocols have therefore been proposed to induce graft tolerance, that is, the survival of an allograft in the absence of continuing immunosuppression. They generally involve pre-transplant conditioning followed by hematopoietic stem cell infusion. Follow-up of immune status is mandatory in this kind of protocol, in order to investigate tolerance and consequently to reduce or withdraw immunosuppression without graft rejection. However, assessment of the alloreactive response using currently available techniques is labor-intensive and requires significant volume of patient's blood. The implementation of such tolerance protocols is thus difficult in routine practice. In this chapter, we describe a novel real-time polymerase chain reaction method based on interferon-gamma and interleukin-2 mRNAs quantification that requires only 10 ml of blood. Moreover, results can be obtained within 48 h. A modified mixed lymphocyte reaction (MLR) using whole blood T lymphocytes as responsive cells and CD3-depleted peripheral blood mononuclear cells (PBMCs) as stimulators is described. An alternative, that is, the use of PBMC as responding cells instead of whole blood, is also depicted. We successfully applied the technique in the monitoring of anti-donor reactivity in living donor liver graft recipients. We suggest that this rapid MLR assay could be valuable for the monitoring of patients undergoing solid organ or hematopoietic stem cell transplantation.