CD8 T cells mediate aortic allograft vasculopathy by direct killing and an interferon-?-dependent indirect pathway

Pathogenetic mechanisms and treatment targets in cerebral malaria

Malaria, the most prevalent mosquito-borne infectious disease worldwide, has accompanied humanity for millennia and remains an important public health issue despite advances in its prevention and treatment. Most infections are asymptomatic, but a small percentage of individuals with a heavy parasite burden develop severe malaria, a group of clinical syndromes attributable to organ dysfunction. Cerebral malaria is an infrequent but life-threatening complication of severe malaria that presents as an acute cerebrovascular encephalopathy characterized by unarousable coma. Despite effective antiparasite drug treatment, 20% of patients with cerebral malaria die from this disease, and many survivors of cerebral malaria have neurocognitive impairment. Thus, an important unmet clinical need is to rapidly identify people with malaria who are at risk of developing cerebral malaria and to develop preventive, adjunctive and neuroprotective treatments for cerebral malaria. This Review describes important advances in the understanding of cerebral malaria over the past two decades and discusses how these mechanistic insights could be translated into new therapies.

Mouse model of alloimmune-induced vascular rejection and transplant arteriosclerosis

Vascular rejection that leads to transplant arteriosclerosis (TA) is the leading representation of chronic heart transplant failure. In TA, the immune system of the recipient causes damage of the arterial wall and dysfunction of endothelial cells and smooth muscle cells. This triggers a pathological repair response that is characterized by intimal thickening and luminal occlusion. Understanding the mechanisms by which the immune system causes vasculature rejection and TA may inform the development of novel ways to manage graft failure. Here, we describe a mouse aortic interposition model that can be used to study the pathogenic mechanisms of vascular rejection and TA. The model involves grafting of an aortic segment from a donor animal into an allogeneic recipient. Rejection of the artery segment involves alloimmune reactions and results in arterial changes that resemble vascular rejection. The basic technical approach we describe can be used with different mouse strains and targeted interventions to answer specific questions related to vascular rejection and TA.

Novel CD8 T cell alloreactivities in CCR5-deficient recipients of class II MHC disparate kidney grafts

Recipient CD4 T regulatory cells inhibit the acute T cell-mediated rejection of renal allografts in wild-type mice. The survival of single class II MHC-disparate H-2(bm12) renal allografts was tested in B6.CCR5(-/-) recipients, which have defects in T regulatory cell activities that constrain alloimmune responses. In contrast to wild-type C57BL/6 recipients, B6.CCR5(-/-) recipients rejected the bm12 renal allografts. However, donor-reactive CD8 T cells rather than CD4 T cells were the primary effector T cells mediating rejection. The CD8 T cells induced to bm12 allografts in CCR5-deficient recipients were reactive to peptides spanning the 3 aa difference in the I-A(bm12) versus I-A(b) β-chains presented by K(b) and D(b) class I MHC molecules. Allograft-primed CD8 T cells from CCR5-deficient allograft recipients were activated during culture either with proinflammatory cytokine-stimulated wild-type endothelial cells pulsed with the I-A(bm12) peptides or with proinflammatory cytokine-simulated bm12 endothelial cells, indicating their presentation of the I-A(bm12) β-chain peptide/class I MHC complexes. In addition to induction by bm12 renal allografts, the I-A(bm12) β-chain-reactive CD8 T cells were induced in CCR5-deficient, but not wild-type C57BL/6, mice by immunization with the peptides. These results reveal novel alloreactive CD8 T cell specificities in CCR5-deficient recipients of single class II MHC renal allografts that mediate rejection of the allografts.

Vascular dysfunction in young, mid-aged and aged mice with latent cytomegalovirus infections

Human cytomegalovirus (HCMV) is associated with vascular diseases in both immunosuppressed and immunocompetent individuals. CMV infections cycle between active and latent phases throughout life. We and others have shown vascular dysfunction during active mouse CMV (mCMV) infections. Few studies have examined changes in physiology during latent CMV infections, particularly vascular responses or whether the negative effects of aging on vascular function and fertility will be exacerbated under these conditions. We measured vascular responses in intact mesenteric and uterine arteries dissected from young, mid-aged, and aged latently mCMV-infected (mCMV genomes are present but infectious virus is undetectable) and age-matched uninfected mice using a pressure myograph. We tested responses to the α(1)-adrenergic agonist phenylephrine, the nitric oxide donor sodium nitroprusside, and the endothelium-dependent vasodilator methacholine. In young latently mCMV-infected mice, vasoconstriction was increased and vasodilation was decreased in mesenteric arteries, whereas both vasoconstriction and vasodilation were increased in uterine arteries compared with those in age-matched uninfected mice. In reproductively active mid-aged latently infected mice, mesenteric arteries showed little change, whereas uterine arteries showed greatly increased vasoconstriction. These vascular effects may have contributed to the decreased reproductive success observed in mid-aged latently mCMV-infected compared with age-matched uninfected mice (16.7 vs. 46.7%, respectively). In aged latently infected mice, vasodilation is increased in mesenteric and uterine arteries likely to compensate for increased vasoconstriction to mediators other than phenylephrine. The novel results of this study show that even when active mCMV infections become undetectable, vascular dysfunction continues and differs with age and artery origin.

Patterns of de novo allo B cells and antibody formation in chronic cardiac allograft rejection after alemtuzumab treatment

Even though the etiology of chronic rejection (CR) is multifactorial, donor specific antibody (DSA) is considered to have a causal effect on CR development. Currently the antibody-mediated mechanisms during CR are poorly understood due to lack of proper animal models and tools. In a clinical setting, we previously demonstrated that induction therapy by lymphocyte depletion, using alemtuzumab (anti-human CD52), is associated with an increased incidence of serum alloantibody, C4d deposition and antibody-mediated rejection in human patients. In this study, the effects of T cell depletion in the development of antibody-mediated rejection were examined using human CD52 transgenic (CD52Tg) mice treated with alemtuzumab. Fully mismatched cardiac allografts were transplanted into alemtuzumab treated CD52Tg mice and showed no acute rejection while untreated recipients acutely rejected their grafts. However, approximately half of long-term recipients showed increased degree of vasculopathy, fibrosis and perivascular C3d depositions at posttransplant day 100. The development of CR correlated with DSA and C3d deposition in the graft. Using novel tracking tools to monitor donor-specific B cells, alloreactive B cells were shown to increase in accordance with DSA detection. The current animal model could provide a means of testing strategies to understand mechanisms and developing therapeutic approaches to prevent chronic rejection.

The link between major histocompatibility complex antibodies and cell proliferation

Experimental evidence indicates that donor-specific antibodies targeting major histocompatibility complex classes I and II molecules can elicit the key features of transplant vasculopathy by acting on the graft vasculature in 3 ways: directly activating proliferative, prosurvival, and migratory signaling in the target endothelial and smooth muscle cells; increasing expression of mitogenic factors in vascular endothelial cells, creating a potential proliferative autocrine loop; and promoting recruitment of inflammatory cells that produce mitogenic factors and elicit chronic inflammation, proliferation, and fibrosis. Here, we review the experimental literature showing the complement and Fc-independent effects of major histocompatibility complex classes I and II antibodies on graft vascular cells that may directly contribute to the proliferative aspect of transplant vasculopathy.

Contribution of B cells and antibody to cardiac allograft vasculopathy

BACKGROUND

The aim of this study was to determine the role of alloantibody in the development of cardiac allograft vasculopathy (AV). AV is the main pathologic indicator of chronic cardiac graft rejection resulting in graft loss at 10 years posttransplant. In AV, a neointimal lesion forms resulting in luminal occlusion and damage to the transplanted organ. AV is T-cell mediated, but the role played by B cells and antibody in AV development has been controversial. No studies have been conducted in the presence of a clinically relevant immunosuppressant. In our study, we use cyclosporin A, a calcineurin inhibitor.

METHODS

Two models of B-cell deficiency were used as recipients of a C3H/HeJ abdominal aortic graft; grafts were harvested at 8 weeks. T- and B-cell immunodeficient mice (RAG1-/-) received passively transferred anti-C3H antibody, raised in B6 mice. Cyclosporin A was administered daily to both control and experimental groups. Alpha-actin staining was used to identify myofibroblasts in the neointima.

RESULTS

Lesions in B-cell-deficient B6 mice were not significantly different in size from those of control mice. Lesions in both B-cell-deficient and wild-type mice showed similar levels of alpha-actin positivity. Passive transfer of antibody to RAG1-/- mice resulted in small, alpha-actin-positive lesions.

CONCLUSIONS

B cells are not required for the development of AV, but the presence of an alloantibody can contribute to AV. We hypothesize that the alloantibody mediates AV by initiating complement-mediated killing of smooth muscle cells, based on an in vitro work. Of interest, we found that the neointimal lesions of B-cell-deficient mice and mice that received antibody showed the presence of alpha-actin in myofibroblasts.

Contribution of pre-existing vascular disease to allograft vasculopathy in a murine model

Allograft vasculopathy (AV) has emerged as a major obstacle for long-term graft survival after cardiac transplantation. The shortage of donor hearts has meant fewer restrictions have been placed on acceptable hearts over the past few years resulting in an increase in the number of older hearts in the donor pool. This increase has subsequently led to the increase of donor hearts containing pre-existing disease. The importance of this pre-existing donor vascular disease in AV outcomes remains controversial. In this study we address this by taking advantage of the fact that B6 Apolipoprotein-E knockout mice develop atherosclerotic lesions in their aortic tracts that closely model human naturally occurring vascular disease. By using these mice as donors, we transplant known levels of pre-existing disease into fully disparate (C3H) recipients. Cyclosporin A is used to prevent acute rejection and allow for allograft vasculopathy. We found that pre-existing lesions are retained in this model after transplantation and that they contribute to increase in lesion size and to increased lumenal narrowing. The de novo AV lesions overlay the pre-existing lesions and this leads to areas of eccentric lesion formation in the vessels with likely accompanying exacerbation of flow perturbation.

Inflammation and atherosclerosis: novel insights into plaque formation and destabilization

BACKGROUND AND PURPOSE

The simplistic view of atherosclerosis as a disorder of pathological lipid deposition has been redefined by the more complex concept of an ongoing inflammatory response.

SUMMARY OF REVIEW

Apolipoprotein E and low-density lipoprotein (LDL)-receptor-deficient mice develop accelerated atherosclerosis allowing in-depth pathophysiological investigations. Atherosclerotic plaques in these mice contain large numbers of T cells and macrophages. Crossbreeding apolipoprotein E-deficient mice with T-cell-deficient mice and mice with impaired macrophage function (osteopetrotic op/op mice) disclosed the important impact of immune cells on atherosclerotic lesion development. In contrast to the detrimental role of T cells and macrophages, B cells appear to be atheroprotective. These basic experimental findings have partly been confirmed in studies of the human carotid artery system. Inflammation is not only instrumental in the development of human atheromatous plaques, but, importantly, plays a crucial role in the destabilization of internal carotid artery plaques, thus converting chronic atherosclerosis into an acute thrombo-embolic disorder. Humoral factors involved in internal carotid artery destabilization include cytokines, cyclooxygenase-2, matrix metalloproteinases, and tissue factor. Antibodies to oxidized LDL can reflect disease activity on one hand, but can also confer atheroprotection. Novel MRI techniques may aid in the in vivo assessment of acute plaque inflammation in humans.

CONCLUSIONS

The impact of inflammation on the development of atherosclerotic plaques and their destabilization opens new avenues for treatment. The effects of statins, acetylsalicyclic acid and angiotensin-converting enzyme inhibitors on stroke prevention may partly be attributable to their profound anti-inflammatory actions. Vaccination against modified LDL and heat shock proteins halt plaque progression in experimental atherosclerosis. Their potential for prevention of human atherosclerosis is currently under investigation.

Aortic allograft vasculopathy is mediated by CD8(+) T cells in Cyclosporin A immunosuppressed mice

We investigated the role of CD4(+) T cells and CD8(+) T cells in mediating allograft vasculopathy in Cyclosporin A (CyA) immunosuppressed mice. We first established that a dose of 50 mg/kg/d CyA was required to prevent acute rejection in C57BL/6 mice. CyA given at 50 mg/kg/d did not prevent allograft vasculopathy in either cardiac or aortic transplants in these mice. Using CD4(-/-) and CD8(-/-) mice, we established that CyA immunosuppression at this dose was only effective at preventing allograft vasculopathy in mice lacking CD8(+) T cells. This implicates CD8(+) T cells in the development of AV in situations of clinical cardiac transplantation where CyA is still the mainstay of immunosuppressive therapy. We confirmed the important role for CD8(+) T cells in AV in the face of CyA immunosuppression by allopriming mice in the presence of CyA and transferring alloprimed T cells into RAG1(-/-) immunodeficient mice. The RAG1(-/-) mice were also treated with CyA. In this situation (CyA present during the allopriming and in the recipient), only primed CD8(+) T cells could mediate AV, primed CD4(+) T cells could not. Alloprimed CD8(+) T cells raised in the presence of CyA exhibited markedly reduced direct recognition responses (as measured by MLR) and effector responses (as measured by cytotoxic activity). In contrast indirect activation was retained. We interpret these data to suggest that in the face of CyA immunosuppression CD4(+) T cell effector function is ablated while CD8(+) T cell function remains partially intact. The in vitro data suggest that the indirect pathway remains intact in this population of CyA resistant CD8(+) T cells.