Critical roles for IL-4, IL-5, and eosinophils in chronic skin allograft rejection

Airway hyperresponsiveness in asthma: The role of the epithelium

Airway hyperresponsiveness (AHR) is a key clinical feature of asthma. The presence of AHR in people with asthma provides the substrate for bronchoconstriction in response to numerous diverse stimuli, contributing to airflow limitation and symptoms including breathlessness, wheeze, and chest tightness. Dysfunctional airway smooth muscle significantly contributes to AHR and is displayed as increased sensitivity to direct pharmacologic bronchoconstrictor stimuli, such as inhaled histamine and methacholine (direct AHR), or to endogenous mediators released by activated airway cells such as mast cells (indirect AHR). Research in in vivo human models has shown that the disrupted airway epithelium plays an important role in driving inflammation that mediates indirect AHR in asthma through the release of cytokines such as thymic stromal lymphopoietin and IL-33. These cytokines upregulate type 2 cytokines promoting airway eosinophilia and induce the release of bronchoconstrictor mediators from mast cells such as histamine, prostaglandin D2, and cysteinyl leukotrienes. While bronchoconstriction is largely due to airway smooth muscle contraction, airway structural changes known as remodeling, likely mediated in part by epithelial-derived mediators, also lead to airflow obstruction and may enhance AHR. In this review, we outline the current knowledge of the role of the airway epithelium in AHR in asthma and its implications on the wider disease. Increased understanding of airway epithelial biology may contribute to better treatment options, particularly in precision medicine.

Antimicrobial peptide-modified AIE visual composite wound dressing for promoting rapid healing of infected wounds

Wound infection is a major problem faced during wound healing. Therefore, it is necessary to develop wound dressings with excellent antimicrobial properties. Here, a smart response system of PVA-TPE/HA-AMP/SF/ALG wound dressing was prepared by a combination of chemical cross-linking and freeze-drying methods. We grafted AMP onto HA to endow the wound dressing with bacterial resistance and slow release of AMP. At the same time, the system detects bacterial activity in real time for precise antimicrobial activity (through the use of PVA-TPE) and modulates inflammation to reduce bacterial infection (through the use of AMP). In addition, the PVA-TPE/HA-AMP/SF/ALG wound dressing has a good three-dimensional mesh structure, which promotes cell proliferation, enhances collagen deposition and angiogenesis, and thus effectively promotes rapid healing of infected wounds. Moreover, it can induce the expression of inflammatory factors such as VEGF, TNF-α, IFN-γ, IL-4 and TGF-β1 in infected wounds through the Wnt/CAMK/p-PKC signaling pathway, inhibit inflammatory responses, promote wound healing and reduce scar formation. Therefore, the PVA-TPE/HA-AMP/SF/ALG wound dressing smart response system shows great promise in infected wound healing.

Relaxin in fibrotic ligament diseases: Its regulatory role and mechanism

Fibrotic ligament diseases (FLDs) are diseases caused by the pathological accumulation of periarticular fibrotic tissue, leading to functional disability around joint and poor life quality. Relaxin (RLX) has been reported to be involved in the development of fibrotic lung and liver diseases. Previous studies have shown that RLX can block pro-fibrotic process by reducing the excess extracellular matrix (ECM) formation and accelerating collagen degradation in vitro and in vivo. Recent studies have shown that RLX can attenuate connective tissue fibrosis by suppressing TGF-β/Smads signaling pathways to inhibit the activation of myofibroblasts. However, the specific roles and mechanisms of RLX in FLDs remain unclear. Therefore, in this review, we confirmed the protective effect of RLX in FLDs and summarized its mechanism including cells, key cytokines and signaling pathways involved. In this article, we outline the potential therapeutic role of RLX and look forward to the application of RLX in the clinical translation of FLDs.

The role of immune response in the pathogenesis of idiopathic pulmonary fibrosis: far beyond the Th1/Th2 imbalance

INTRODUCTION

. Idiopathic pulmonary fibrosis (IPF) is a chronic disease of unknown origin characterized by progressive scarring of the lung leading to irreversible loss of function. Despite the availability of two drugs that are able to slow down disease progression, IPF remains a deadly disease. The pathogenesis of IPF is poorly understood, but a dysregulated wound healing response following recurrent alveolar epithelial injury is thought to be crucial. Areas covered. In the last few years, the role of the immune system in IPF pathobiology has been reconsidered; indeed, recent data suggest that a dysfunctional immune system may promote and unfavorable interplay with pro-fibrotic pathways thus acting as a cofactor in disease development and progression. In this article, we review and critically discuss the role of T cells in the pathogenesis and progression of IPF in the attempt to highlight ways in which further research in this area may enable the development of targeted immunomodulatory therapies for this dreadful disease.

EXPERT OPINION

A better understanding of T cells interactions has the potential to facilitate the development of immune modulators targeting multiple T cell-mediated pathways thus halting disease initiation and progression.

Immune Cells in Subretinal Wound Healing and Fibrosis

The subretinal space is devoid of any immune cells under normal conditions and is an immune privileged site. When photoreceptors and/or retinal pigment epithelial cells suffer from an injury, a wound healing process will be initiated. Retinal microglia and the complement system, as the first line of retinal defense, are activated to participate in the wound healing process. If the injury is severe or persists for a prolonged period, they may fail to heal the damage and circulating immune cells will be summoned leading to chronic inflammation and abnormal wound healing, i.e., subretinal or intraretinal fibrosis, a sight-threatening condition frequently observed in rhematogenous retinal detachment, age-related macular degeneration and recurrent uveoretinitis. Here, we discussed the principles of subretinal wound healing with a strong focus on the conditions whereby the damage is beyond the healing capacity of the retinal defense system and highlighted the roles of circulating immune cells in subretinal wound healing and fibrosis.

Time-dependent blood eosinophilia count increases the risk of kidney allograft rejection

Background

Growing evidence suggest that type 2 immune effectors play a role in solid organ transplantation. The aim of this study was to evaluate the impact of blood count eosinophils (BCEo) on immunological outcomes in kidney transplant recipients with stable graft function after 3 months post-transplant.

Method

We performed cause-specific Cox model considering BCEo, the use of calcineurin inhibitors and systemic corticoids as time-dependent explicative variables on a prospective cohort of 1013 kidney transplant patients who experienced kidney allograft rejection and/or the appearance of de novo donor specific antibodies after excluding common causes of increased BCEo..

Findings

BCEo ≥ 0.3 G/L was associated with a 3-fold increased risk of rejection independent of immunosuppressive regimen after 3 months post-transplant in patients without pre-transplant DSAs and with CNI-based immunosuppression. No association between BCEo either with donor specific antibodies or graft survival was noticed.

Interpretation

These observations in this large cohort support the hypothesis of eosinophils in allo-immunity in human and claim for further mechanistic research.

Funding

This study was supported by the French National Research Agency, The “Institut de Recherche en Santé Respiratoire des Pays de la Loire” and the University hospital of Nantes.

Methods to Detect MHC-Specific IgE in Mice and Men

Humoral immunity is a major barrier limiting long-term outcome after organ transplantation. Especially, the production of antibodies directed against donor HLA/MHC antigens (i.e. donor-specific antibodies (DSA)) leading to antibody-mediated rejection (ABMR) is considered to be a major factor negatively affecting allograft survival. DSAs of the IgG isotype are routinely measured in transplant patients. However, not all patients diagnosed with IgG-DSA develop ABMR events. Therefore, research in better understanding the mechanisms of ABMR is of great importance. We recently demonstrated the production of MHC-specific IgE upon allograft rejection in mice and in transplant patients. IgE is classically connected with allergy and is known to be important for the humoral defense against helminths and worms. However, its role in autoimmune diseases and cancer has been reported recently as well. The concentration of IgE in blood is extremely low compared to other antibody isotypes. Therefore, detection of MHC-specific IgE from serum requires methods of high sensitivity. Since MHC-specific IgG-typically present at much higher serum levels-develops as well, high specificity is also required of IgE detection methods. In the murine model we developed an enzyme linked immunosorbent assay (ELISA) using MHC monomers for measurement of MHC-specific IgE, allowing us to distinguish between specificities of antibodies against different class I and class II antigens. For measurement of functional activity of MHC-specific IgE in vitro, a release assay using a rat basophil cell line (RBL-2H3) was established. For functional analysis of MHC-specific IgE in vivo, a cutaneous hypersensitivity reaction assay was adapted for this purpose using MHC monomers. Humanized RBL-2H3 cells transfected with cDNA coding for the human-high affinity IgE receptor were used for functionality measurement of donor-specific IgE in sensitized transplant patients. For detection of HLA-specific IgE, a bead assay was adapted, using beads expressing single HLA antigens. The aim of this publication is to demonstrate currently established methods for the detection and characterization of MHC-specific IgE in the murine and human setting.

The IL-4/IL-13 axis in skin fibrosis and scarring: mechanistic concepts and therapeutic targets

Skin fibrosis, characterized by excessive fibroblast proliferation and extracellular matrix deposition in the dermis, is the histopathologic hallmark of dermatologic diseases such as systemic sclerosis, hypertrophic scars, and keloids. Effective anti-scarring therapeutics remain an unmet need, underscoring the complex pathophysiologic mechanisms of skin fibrosis. The Th2 cytokines interleukin (IL)-4 and IL-13 have been implicated as key mediators in the pathogenesis of fibroproliferative disorders. The goal of this article is to summarize the current understanding of the role of the IL-4/IL-13 axis in wound healing and skin fibrosis. We conducted a literature search to identify research studies investigating the roles of IL-4 and IL-13 in fibrotic skin diseases. While transforming growth factor-beta has long been regarded as the main driver of fibrotic processes, research into the cellular and molecular biology of wound healing has revealed other pathways that promote scar tissue formation. IL-4 and IL-13 are important mediators of skin fibrosis, supported by evidence from in vitro data, animal models of fibrosis, and clinical studies. Overactive signaling of the IL-4/IL-13 axis contributes to the initiation and perpetuation of fibrotic skin diseases. Further insights into the IL-4/IL-13 axis may reveal potential targets for the development of novel therapies that prevent or treat fibrotic skin diseases.

Serological cytokine profiles of cardiac rejection and lung infection after heart transplantation in rats

BACKGROUND

Allograft rejection and infection are the major sources of morbidity and mortality after heart transplant. Early differential diagnosis is clinically crucial but difficult. The aim of the study was to examine serum cytokine profiles associated with each entity and whether such profiles could help to differentiate between them.

METHODS

Heart allografts from Wistar rats were transplanted to Lewis rats as described by Yokoyama. Cardiac rejection and pulmonary bacterial infection were induced by Cyclosporine cessation and bacteria bronchus injection, and pathologically confirmed. Ninety serological cytokines profiles of the study objects were then simultaneously measured using a biotin label-based cytokine array. The fold change (FC) was used for relative cytokine concentration comparison analysis.

RESULTS

Four cytokines in cardiac rejection group were significantly dysregulated as compared to health controls (β -Catenin, 0.51 FC; E-Selectin, 0.62 FC; IFN-gamma, 1.87 FC; and IL-13, 0.60 FC, respectively). In pulmonary infection animals, 11 cytokines were remarkably dysregulated in comparison with the control group (CINC-3, 0.57 FC; CNTF R alpha, 0.59 FC; E-Selectin, 0.58 FC; FSL1,0.62 FC; Hepassocin, 0.64 FC; IL-2, 0.26 FC; IL-13, 0.49 FC; NGFR, 0.57 FC; RAGE, 0.50 FC; TIMP-1, 0.49 FC; and IFN-gamma, 1.77 FC, respectively). Eleven cytokines were significantly up-regulated in cardiac rejection group comparing to the pulmonary infection animals (FSL1, 2.32FC; Fractalkine, 1.65FC; GFR alpha-1, 1.64FC; IL-2, 2.72FC; IL-5, 1.60FC; MMP-2, 1.71FC; NGFR, 2.25FC; TGF-beta1, 1.58FC; TGF-beta3, 1.58FC; Thrombospondin, 1.64FC, and TIMP-1, 1.52FC, respectively).

CONCLUSIONS

The current study illustrated the disease-specific serological cytokine profiles of allograft rejection and pulmonary bacterial infection after cardiac transplant. Such disease associated cytokine portraits might have the potential for early discrimination diagnosis.

The role of myofibroblasts in wound healing

The importance of proper skin wound healing becomes evident when our body's repair mechanisms fail, leading to either non-healing (chronic) wounds or excessive repair (fibrosis). Chronic wounds are a tremendous burden for patients and global healthcare systems and are on the rise due to their increasing incidence with age and diabetes. Curiously, these same risk factors also sign responsible for the development of hypertrophic scarring and organ fibrosis. Activated repair cells - myofibroblasts - are the main producers and organizers of extracellular matrix which is needed to restore tissue integrity after injury. Too many myofibroblasts working for too long cause tissue contractures that ultimately obstruct organ function. Insufficient myofibroblast activation and activities, in turn, prevents normal wound healing. This short review puts a spotlight on the myofibroblast for those who seek therapeutic targets in the context of dysregulated tissue repair. "Keep your myofibroblasts in balance" is the message.

Inhibition of histone methyltransferase EZH2 ameliorates early acute renal allograft rejection in rats

BACKGROUND

Although histone methyltransferases EZH2 has been proved to have significant regulatory effect on the immune rejection after hematopoietic stem cell transplantation, its role in solid-organ transplantation remains uncovered. In this study, we investigate whether histone methylation regulation can impact renal allograft rejection in rat models.

RESULTS

Allogeneic rat renal transplantation model (Wistar to Lewis) was established, and the recipients were administrated with EZH2 inhibitor DZNep after transplantation. Renal allografts and peripheral blood were collected on day 5 after transplantation for histological examination and mechanism investigation. We found that inhibition of EZH2 by DZNep after transplantation significantly ameliorated acute rejection (AR), with decreased histological injury and reduced inflammatory infiltration in renal allografts. Attenuation of AR was due to the prohibited activation of alloreactive T cells, the subsequent impaired production of inflammatory cytokines, and also the elevated apoptosis of alloreactive T cells in both renal allografts and periphery. However, inhibition of EZH2 did not increase the regulatory T cells during the AR.

CONCLUSIONS

Disruption of EZH2 by DZNep suppressed the immune responses of alloreactive T cells and ameliorated AR of renal allografts. This suggests a therapeutic potential of targeting histone methyltransferases EZH2 in treating allograft rejection after solid organ transplantation.

Type I Interferons Regulate the Magnitude and Functionality of Mouse Polyomavirus-Specific CD8 T Cells in a Virus Strain-Dependent Manner

Mouse polyomavirus (MPyV) is a ubiquitous persistent natural mouse pathogen. A glutamic acid (E)-to-glycine (G) difference at position 91 of the VP1 capsid protein shifts the profile of tumors induced by MPyV from an epithelial to a mesenchymal cell origin. Here we asked if this tropism difference affects the MPyV-specific CD8 T cell response, which controls MPyV infection and tumorigenesis. Infection by the laboratory MPyV strain RA (VP1-91G) or a strain A2 mutant with an E-to-G substitution at VP1 residue 91 [A2(91G)] generated a markedly smaller virus-specific CD8 T cell response than that induced by A2(VP1-91E) infection. Mutant A2(91G)-infected mice showed a higher frequency of memory precursor (CD127(hi) KLRG1(lo)) CD8 T cells and a higher recall response than those of A2-infected mice. Using T cell receptor (TCR)-transgenic CD8 T cells and immunization with peptide-pulsed dendritic cells, we found that early bystander inflammation associated with A2 infection contributed to recruitment of the larger MPyV-specific CD8 T cell response. Beta interferon (IFN-β) transcripts were induced early during A2 or A2(91G) infections. IFN-β inhibited replication of A2 and A2(91G) in vitro Using mice lacking IFN-αβ receptors (IFNAR(-/-)), we showed that type I IFNs played a role in controlling MPyV replication in vivo but differentially affected the magnitude and functionality of virus-specific CD8 T cells recruited by A2 and A2(91G) viral infections. These data indicate that type I IFNs are involved in protection against MPyV infection and that their effect on the antiviral CD8 T cell response depends on capsid-mediated tropism properties of the MPyV strain.

IMPORTANCE

Isolates of the human polyomavirus JC virus from patients with the frequently fatal demyelinating brain disease progressive multifocal leukoencephalopathy (PML) carry single amino acid substitutions in the domain of the VP1 capsid protein that binds the sialic acid moiety of glycoprotein/glycolipid receptors on host cells. These VP1 mutations may alter neural cell tropism or enable escape from neutralizing antibodies. Changes in host cell tropism can affect recruitment of virus-specific CD8 T cells. Using mouse polyomavirus, we demonstrate that a single amino acid difference in VP1 known to shift viral tropism profoundly affects the quantity and quality of the anti-polyomavirus CD8 T cell response and its differentiation into memory cells. These findings raise the possibility that CD8 T cell responses to infections by human polyomaviruses may be influenced by VP1 mutations involving domains that engage host cell receptors.

A Player and Coordinator: The Versatile Roles of Eosinophils in the Immune System

Eosinophils have traditionally been associated with allergic diseases and parasite infection. Research advances in the recent decades have brought evolutionary changes in our understanding of eosinophil biology and its roles in immunity. It is currently recognized that eosinophils play multiple roles in both innate and adaptive immunity. As effector cells in innate immunity, eosinophils exert a pro-inflammatory and destructive role in the Th2 immune response associated with allergic inflammation or parasite infection. Eosinophils can also be recruited by danger signals released by pathogen infections or tissue injury, inducing host defense against parasitic, fungal, bacterial or viral infection or promoting tissue repair and remodeling. Eosinophils also serve as nonprofessional antigen-presenting cells in response to allergen challenge or helminth infection, and, meanwhile, are known to function as a versatile coordinator that actively regulates or interacts with various immune cells including T lymphocytes and dendritic cells. More roles of eosinophils implicated in immunity have been proposed including in immune homeostasis, allograft rejection, and anti-tumor immunity. Eosinophil interactions with structural cells are also implicated in the mechanisms in allergic inflammation and in Helicobacter pylori gastritis. These multifaceted roles of eosinophils as both players and coordinators in immune system are discussed in this review.

Chronic Renal Transplant Rejection and Possible Anti-Proliferative Drug Targets

The global prevalence of renal transplants is increasing with time, and renal transplantation is the only definite treatment for end-stage renal disease. We have limited the acute and late acute rejection of kidney allografts, but the long-term survival of renal tissues still remains a difficult and unanswered question as most of the renal transplants undergo failure within a decade of their transplantation. Among various histopathological changes that signify chronic allograft nephropathy (CAN), tubular atrophy, fibrous thickening of the arteries, fibrosis of the kidney interstitium, and glomerulosclerosis are the most important. Moreover, these structural changes are followed by a decline in the kidney function as well. The underlying mechanism that triggers the long-term rejection of renal transplants involves both humoral and cell-mediated immunity. T cells, with their related cytokines, cause tissue damage. In addition, CD 20+ B cells and their antibodies play an important role in the long-term graft rejection. Other risk factors that predispose a recipient to long-term graft rejection include HLA-mismatching, acute episodes of graft rejection, mismatch in donor-recipient age, and smoking. The purpose of this review article is the analyze current literature and find different anti-proliferative agents that can suppress the immune system and can thus contribute to the long-term survival of renal transplants. The findings of this review paper can be helpful in understanding the long-term survival of renal transplants and various ways to improve it.

Leukocytes: The Double-Edged Sword in Fibrosis

Skin tissue scar formation and fibrosis are often characterized by the increased production and deposition of extracellular matrix components, accompanied by the accumulation of a vast number of myofibroblasts. Scaring is strongly associated with inflammation and wound healing to regain tissue integrity in response to skin tissue injury. However, increased and uncontrolled inflammation, repetitive injury, and individual predisposition might lead to fibrosis, a severe disorder resulting in the formation of dense and stiff tissue that loses the physical properties and physiological functions of normal tissue. Fibrosis is an extremely complicated and multistage process in which bone marrow-derived leukocytes act as both pro- and antifibrotic agents, and therefore, few, if any, effective therapies are available for the most severe and lethal forms of fibrosis. Herein, we discuss the current knowledge on the multidimensional impact of leukocytes on the induction of fibrosis, focusing on skin fibrosis.

Sclerosing peritonitis, a rare complication after intestinal transplant. Report of one case successfully treated with adjustment of immunosuppression

Sclerosing peritonitis is a complication described in different clinical situations, such as patients that underwent prolonged peritoneal dialysis or renal transplantation with previous history of peritoneal dialysis. The origin of this entity is unclear so far and it is believed that several mechanisms may contribute to its development. The hallmark of sclerosing peritonitis is the continuous accumulation of fibrocollagenous deposits in the intestinal wall and mesenteries causing progressive adhesion of the intestinal loops and mesenteric retraction resulting in intestinal obstruction. Also, it has been described as a rare complication after intestinal transplant that might lead to graft failure. In this report, we describe a case of sclerosing peritonitis after intestinal transplantation that was successfully treated with modifications in the immunosuppressive regime allowing restitution of gastrointestinal transit and intestinal autonomy.

Cytokine mediated tissue fibrosis

Acute inflammation is a recognised part of normal wound healing. However, when inflammation fails to resolve and a chronic inflammatory response is established this process can become dysregulated resulting in pathological wound repair, accumulation of permanent fibrotic scar tissue at the site of injury and the failure to return the tissue to normal function. Fibrosis can affect any organ including the lung, skin, heart, kidney and liver and it is estimated that 45% of deaths in the western world can now be attributed to diseases where fibrosis plays a major aetiological role. In this review we examine the evidence that cytokines play a vital role in the acute and chronic inflammatory responses that drive fibrosis in injured tissues. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Long-term prevention of chronic allograft rejection by regulatory T-cell immunotherapy involves host Foxp3-expressing T cells

Administration of donor-specific regulatory T cells prevents chronic rejection of BM and skin allografts in the mouse. Injected regulatory T cells induce the emergence of host regulatory T cells with similar specificity thus ensuring persistence of tolerance.

Negligible immunogenicity of terminally differentiated cells derived from induced pluripotent or embryonic stem cells

The advantages of using induced pluripotent stem cells (iPSCs) instead of embryonic stem (ES) cells in regenerative medicine centre around circumventing concerns about the ethics of using ES cells and the likelihood of immune rejection of ES-cell-derived tissues. However, partial reprogramming and genetic instabilities in iPSCs could elicit immune responses in transplant recipients even when iPSC-derived differentiated cells are transplanted. iPSCs are first differentiated into specific types of cells in vitro for subsequent transplantation. Although model transplantation experiments have been conducted using various iPSC-derived differentiated tissues and immune rejections have not been observed, careful investigation of the immunogenicity of iPSC-derived tissue is becoming increasingly critical, especially as this has not been the focus of most studies done so far. A recent study reported immunogenicity of iPSC- but not ES-cell-derived teratomas and implicated several causative genes. Nevertheless, some controversy has arisen regarding these findings. Here we examine the immunogenicity of differentiated skin and bone marrow tissues derived from mouse iPSCs. To ensure optimal comparison of iPSCs and ES cells, we established ten integration-free iPSC and seven ES-cell lines using an inbred mouse strain, C57BL/6. We observed no differences in the rate of success of transplantation when skin and bone marrow cells derived from iPSCs were compared with ES-cell-derived tissues. Moreover, we observed limited or no immune responses, including T-cell infiltration, for tissues derived from either iPSCs or ES cells, and no increase in the expression of the immunogenicity-causing Zg16 and Hormad1 genes in regressing skin and teratoma tissues. Our findings suggest limited immunogenicity of transplanted cells differentiated from iPSCs and ES cells.

Deleterious effect of CTLA4-Ig on a Treg-dependent transplant model

Blockade of the B7:CD28 costimulatory pathway has emerged as a promising therapy to prevent allograft rejection. However, results from the belatacept phase III clinical trial demonstrated a higher rejection rate when compared to cyclosporine, raising concern about potential deleterious effects of this agent. In this study, we investigated the consequences of B7:CD28 blockade by hCTLA4Ig on regulator T cell (Treg) generation in different major histocompatibility complex (MHC) mismatch transplant models. Administration of hCTLA4Ig significantly decreased the amount of Tregs in B6 WT animals and this effect was predominant in thymus-induced Tregs (Helios(+) ). Although hCTLA4Ig prevented rejection in a fully allogeneic mismatch model, it accelerated rejection in a MHC class-II mismatch model (MST = 26, p < 0.0001), in which long-term allograft survival is dependent on Tregs. This accelerated rejection was associated with a marked reduction in thymus-induced Tregs and led to a higher effector/regulatory T-cell ratio in secondary lymphoid organs and in the allograft. This study confirms the importance of the B7:CD28 pathway in Treg homeostasis in an in vivo transplant model and suggests that hCTLA4Ig therapy may be deleterious in circumstances where engraftment is dependent on Tregs.

The role of atopy in corneal graft survival in keratoconus

PURPOSE

To compare the prevalence of endothelial rejection episodes and the probability of graft survival after initial and repeat penetrating keratoplasty (PK) in patients with keratoconus with and without atopy.

METHODS

A retrospective review was conducted of all patients receiving PK for keratoconus at the University of Texas Southwestern Medical Center at Dallas from 1988 to 2009. Inclusion criteria involved those with both an International Classification of Diseases-9 code for keratoconus and a Current Procedural Terminology code for PK based on a computer database search. Patients younger than 18 years were excluded. These records were then reviewed for a history of atopic disorders. The main outcome measures included the prevalence of endothelial rejection episodes and the probability of graft survival. The probability of corneal graft survival in patients with and without a history of atopy was compared using the Kaplan-Meier method.

RESULTS

There were 168 grafts in 122 patients. There were 66 (39.2%) and 102 (60.8%) grafts with and without a history of atopy, respectively. Bilateral first grafts were required in 32 patients, 14 and 18 patients with and without a history of atopy, respectively. The atopic and nonatopic groups had no significant differences with respect to age, preexisting ocular conditions, concomitant surgical procedures, and length of follow-up. Men received first grafts significantly more frequently than women in the nonatopic group (P = 0.029); however, there was no sex difference in repeat grafts. There were no significant differences in the prevalence of endothelial rejection episodes after the first (P = 0.716), second (P > 0.999), and third or further grafts (P > 0.999). Graft survival between the atopic and nonatopic groups did not differ significantly in the first (P = 0.881), second (P = 0.752), or third or further graft (P = 0.157). Among first grafts in the atopic group, no statistically significant difference in survival existed among patients analyzed with different manifestations of atopy (P = 0.061). One episode of allograft endothelial rejection created a statistically significant difference in ultimate graft survival probability in both the atopic (P = 0.003) and nonatopic (P = 0.002) groups.

CONCLUSIONS

Among patients with keratoconus receiving PK, there is no statistically significant difference in the prevalence of endothelial graft rejection episodes or probability of graft survival between patients with and without a clinical history of atopy.

PPAR-γ signaling and IL-5 inhibition together prevent chronic rejection of MHC Class II-mismatched cardiac grafts

BACKGROUND

Chronic rejection can prevent long-term survival of organ transplants. Although the beneficial effects of peroxisome proliferator-activated receptor-gamma (PPAR-γ) in reducing graft rejection have been reported, the details of the underlying mechanisms remain unclear, especially in the context of modulating cellular infiltration and preventing vasculopathy and interstitial fibrosis.

METHODS

The therapeutic effects of the PPAR-γ agonist, rosiglitazone, combined with anti-interleukin-5 are explored in a mouse model of MHC Class II-histoincompatible cardiac transplantation.

RESULTS

Rosiglitazone treatment alone marginally increased long-term survival and reduced CD8 T-cell infiltration and vasculopathy in the grafts. However, there was no reduction in collagen deposition and interleukin (IL)-4, IL-5 and eosinophil infiltration were increased. Anti-IL-5 antibody treatment alone reduced eosinophil infiltration and collagen deposition, but had no effect on CD8 T-cell infiltration or vasculopathy. Combined treatment with anti-IL-5 antibody and rosiglitazone prevented graft rejection. Furthermore, rosiglitazone treatment increased adiponectin receptor II expression in grafts and on dendritic cells and T cells in vitro. Graft survival correlated with increased expression in grafts of the inhibitory molecule PD-L1.

CONCLUSIONS

The findings obtained increase the knowledge on the mode of action of rosiglitazone in promoting the survival of MHC Class II-mismatched cardiac transplants in which the CD8 T cells and eosinophils play key roles. PPAR-γ signaling combined with IL-5 blockade prevents graft rejection.

Antifibrosis: to reverse the irreversible

Fibrosis is a pathological process that includes scar formation and overproduction of extracellular matrix by the connective tissue as a response to tissue damage. The fibrotic process involves multiple organs and results in progressive life-threatening diseases. Today, we know more about the molecular mechanism that leads to fibrosis involving different type of cells, cytokines, chemokines, and tissue enzymes. Fibrosis was considered an irreversible process, at least clinically, and is still usually treated by anti-inflammatory and immunosuppressive agents. No proven antifibrotic therapy has shown efficacy in ameliorating the clinical course of fibrotic diseases, but our current understanding led to the development of different drugs with promising results, like: mycophenolate mofetil, interferon, relaxin, and intravenous immunoglobulin. This review will provide a glance to this heavily investigated subject.

Allergic conjunctivitis exacerbates corneal allograft rejection by activating Th1 and th2 alloimmune responses

Allergic conjunctivitis (AC) and airway hyperreactivity exacerbate corneal allograft rejection. Because AC and airway hyperreactivity are allergic diseases of mucosal tissues, we determined whether an allergic disease of a nonmucosal tissue would affect corneal allograft rejection and whether Th2 cells alone accounted for accelerated graft rejection in allergic mice. Hosts sensitized cutaneously with short ragweed pollen developed cutaneous immediate hypersensitivity but rejected corneal allografts at the same tempo and incidence as naive mice. Th2 immune deviation induced with keyhole limpet hemocyanin and IFA did not affect corneal allograft rejection. Thus, Th2 immune deviation alone does not account for the exacerbation of corneal allograft rejection that occurs in mice with AC. CD4(+) T cells from AC mice elaborated Th1 (IFN-gamma) and Th2 (IL-13) cytokines when challenged with donor alloantigens. Adoptive transfer of Th1 or Th2 cells to nude mice, from AC mice that had rejected corneal allografts, produced graft rejection in 70% and 20% of the hosts, respectively. In contrast, adoptive transfer of a combination of Th1 and Th2 cells produced 100% rejection. Administration of exogenous IFN-gamma could substitute for Th1 cells and produced 100% corneal allograft rejection in recipients of Th2 cells alone. By contrast, IFN-gamma did not significantly enhance corneal allograft rejection mediated by Th1 cells. Thus, exacerbation of corneal allograft rejection in mice with AC is associated with a mixed Th1 and Th2 alloimmune response, and the contribution of Th1 cells is through their production of IFN-gamma.

Mechanism of cellular rejection in transplantation

The explosion of new discoveries in the field of immunology has provided new insights into mechanisms that promote an immune response directed against a transplanted organ. Central to the allograft response are T lymphocytes. This review summarizes the current literature on allorecognition, costimulation, memory T cells, T cell migration, and their role in both acute and chronic graft destruction. An in depth understanding of the cellular mechanisms that result in both acute and chronic allograft rejection will provide new strategies and targeted therapeutics capable of inducing long-lasting, allograft-specific tolerance.

Donor IL-4-treatment induces alternatively activated liver macrophages and IDO-expressing NK cells and promotes rat liver allograft acceptance

Most approaches to transplant tolerance involve treatment of the recipient to prevent rejection. This study investigates donor treatment with IL-4 for its effect on subsequent rat liver allograft survival. Rat orthotopic liver transplants were performed in rejecting (PVG donor to Lewis recipient) or spontaneously tolerant (PVG to DA) strain combinations. Donors were untreated or injected intraperitoneally with IL-4 (30,000U/day) for 5days. Tissue infiltrates and gene expression were examined by immunohistochemistry and real-time quantitative PCR. IL-4 induced a marked leukocyte infiltrate in donor livers prior to transplant. Macrophages comprised the major population, although B cells, T cells and natural killer (NK) cells also increased. IL-4-induced liver macrophages had an alternatively activated phenotype with increased expression of mannose receptor but not inducible nitric oxide synthase (NOS2). IL-4 also induced IDO and IFN-gamma expression by NK cells. Donor IL-4-treatment converted rejection to acceptance in the majority of Lewis recipients (median survival time >96days) and did not prevent acceptance in DA recipients. Acceptance in Lewis recipients was associated with increased donor cell migration to recipient spleens and increased splenic IL-2, IFN-gamma and IDO expression 24h after transplantation. Donor IL-4-treatment increased leukocytes in the donor liver including potentially immunosuppressive populations of alternatively activated macrophages and IDO-expressing NK cells. Donor treatment led to long-term acceptance of most livers in association with early immune activation in recipient lymphoid tissues.

Role of IL-4 and Th2 responses in allograft rejection and tolerance

PURPOSE OF REVIEW

Due to the dominance of Th1 cytokines in rejection and the ability of Th2 cytokines, particularly IL-4, to inhibit Th1 responses, it has long been held that Th2 cytokines can improve transplant outcomes. Although there is some support for this, there is mounting evidence that IL-4 and Th2 cytokines can promote graft dysfunction. These disparate effects are reviewed.

RECENT FINDINGS

The role of Th2 cytokines in graft dysfunction is not necessarily due to promotion of humoral immunity, but is due to their ability to drive T-cell and non-T-cell responses including alternative activation of macrophages. Alternatively, activated macrophages compete with classically activated macrophages for arginine and they are mutually exclusive, analogous to mutual competition between Th1 and Th2 cells. Recent findings also point to two subsets of regulatory T cells (Tregs), each dependent on either Th1 or Th2 cytokines. In addition to its effects on bone marrow-derived cells, IL-4 affects parenchymal cells by signalling through the type II receptor, which consists of the IL-4R alpha chain (IL-4Ralpha) and the IL-13Ralpha1, which also binds IL-13.

SUMMARY

The effects of Th2 cytokines in transplantation depend on their cellular targets, the timing and form of administration and on Th2 cytokine-dependent Tregs.

Allergic airway hyperreactivity increases the risk for corneal allograft rejection

Corneal allografts transplanted into hosts with allergic conjunctivitis experience an increased incidence and swifter tempo of immune rejection compared to corneal allografts transplanted to nonallergic hosts. Previous findings suggested that increased risk for rejection was not a local effect produced by an inflamed eye, but was due to perturbation of the systemic immune responses to alloantigens on the corneal allograft. We tested the hypothesis that another allergic disease, airway hyperreactivity (AHR), would also increase the risk for corneal allograft rejection. Induction of AHR with either ovalbumin (OVA) or short ragweed (SRW) extract prior to keratoplasty resulted in a steep increase in the speed and incidence of corneal allograft rejection. Delayed-type hypersensitivity (DTH) responses to corneal alloantigens were closely associated with corneal allograft rejection. However, the deleterious effect of AHR on corneal allograft survival was not reflected in a heightened magnitude of allospecific DTH, cytotoxic T lymphocyte and lymphoproliferative responses to the alloantigens on the corneal allograft. Unlike Th2-based immediate hypersensitivity, CD8+ T-cell-based contact hypersensitivity to oxazolone did not increase the risk for corneal allograft rejection. Thus, Th2-based allergic diseases significantly reduce the immune privilege of the corneal allograft and represent important risk factors for consideration in the atopic patient.

OX40 costimulation prevents allograft acceptance induced by CD40-CD40L blockade

Disrupting the CD40-CD40L costimulation pathway promotes allograft acceptance in many settings. Herein, we demonstrate that stimulating OX40 overrides cardiac allograft acceptance induced by disrupting CD40-CD40L interactions. This effect of OX40 stimulation was dependent on CD4(+) T cells, which in turn provided help for CD8(+) T cells and B cells. Allograft rejection was associated with donor-reactive Th1 and Th2 responses and an unconventional granulocytic infiltrate and thrombosis of the arteries. Interestingly, OX40 stimulation induced a donor-reactive IgG class switch in the absence of CD40-CD40L interactions, and the timing of OX40 stimulation relative to transplantation affected the isotype of donor-reactive Ab produced. Inductive OX40 stimulation induced acute graft rejection, which correlated with both IgG1 and IgG2a deposition within the graft. Once graft acceptance was established following CD40-CD40L blockade, delayed OX40 stimulation did not induce acute allograft rejection despite priming of graft-reactive Th1 and Th2. Rather, chronic rejection was induced, which was characterized by IgG1 but not IgG2a deposition within the graft. These studies reveal both redundancy and key differences in function among costimulatory molecules that manifest in distinct pathologies of allograft rejection. These findings may help guide development of therapeutics aimed at promoting graft acceptance in transplant recipients.

Potential cellular and molecular causes of hypertrophic scar formation

A scar is an expected result of wound healing. However, in some individuals, and particularly in burn victims, the wound healing processes may lead to a fibrotic hypertrophic scar, which is raised, red, inflexible and responsible for serious functional and cosmetic problems. It seems that a wide array of subsequent processes are involved in hypertrophic scar formation, like an affected haemostasis, exaggerated inflammation, prolonged reepithelialization, overabundant extracellular matrix production, augmented neovascularization, atypical extracellular matrix remodeling and reduced apoptosis. Platelets, macrophages, T-lymphocytes, mast cells, Langerhans cells and keratinocytes are directly and indirectly involved in the activation of fibroblasts, which in turn produce excess extracellular matrix. Following the chronology of normal wound healing, we unravel, clarify and reorganize the complex molecular and cellular key processes that may be responsible for hypertrophic scars. It remains unclear whether these processes are a cause or a consequence of unusual scar tissue formation, but raising evidence exists that immunological responses early following wounding play an important role. Therefore, when developing preventive treatment modalities, one should aim to put the early affected wound healing processes back on track as quickly as possible.

Transplant acceptance following anti-CD4 versus anti-CD40L therapy: evidence for differential maintenance of graft-reactive T cells

Inductive therapy with anti-CD4 or anti-CD40L monoclonal antibodies (mAb) leads to long-term allograft acceptance but the immune parameters responsible for graft maintenance are not well understood. This study employed an adoptive transfer system in which cells from mice bearing long-term cardiac allografts following inductive anti-CD4 or anti-CD40L therapy were transferred into severe combined immunodeficiency (SCID) allograft recipients. SCID recipients of cells from anti-CD4-treated mice (anti-CD4 cells) did not reject allografts while those receiving cells from anti-CD40L-treated mice (anti-CD40L cells) did reject allografts. Carboxyfluorescein succinimidyl ester (CFSE) labeling of transferred cells revealed that this difference was not associated with differential proliferative capacities of these cells in SCID recipients. Like cells from naïve mice, anti-CD40L cells mounted a Th1 response following transfer while anti-CD4 cells mounted a dominant Th2 response. Early (day 10) T-cell priming was detectable in both groups of primary allograft recipients but persisted to day 30 only in recipients treated with anti-CD4 mAb. Thus, anti-CD40L therapy appears to result in graft-reactive T cells with a naïve phenotype while anti-CD4 therapy allows progression to an altered state of differentiation. Additional data herein support the notion that anti-CD40L mAb targets activated, but not memory, cells for removal or functional silencing.

Cellular and molecular mechanisms of fibrosis

Fibrosis is defined by the overgrowth, hardening, and/or scarring of various tissues and is attributed to excess deposition of extracellular matrix components including collagen. Fibrosis is the end result of chronic inflammatory reactions induced by a variety of stimuli including persistent infections, autoimmune reactions, allergic responses, chemical insults, radiation, and tissue injury. Although current treatments for fibrotic diseases such as idiopathic pulmonary fibrosis, liver cirrhosis, systemic sclerosis, progressive kidney disease, and cardiovascular fibrosis typically target the inflammatory response, there is accumulating evidence that the mechanisms driving fibrogenesis are distinct from those regulating inflammation. In fact, some studies have suggested that ongoing inflammation is needed to reverse established and progressive fibrosis. The key cellular mediator of fibrosis is the myofibroblast, which when activated serves as the primary collagen-producing cell. Myofibroblasts are generated from a variety of sources including resident mesenchymal cells, epithelial and endothelial cells in processes termed epithelial/endothelial-mesenchymal (EMT/EndMT) transition, as well as from circulating fibroblast-like cells called fibrocytes that are derived from bone-marrow stem cells. Myofibroblasts are activated by a variety of mechanisms, including paracrine signals derived from lymphocytes and macrophages, autocrine factors secreted by myofibroblasts, and pathogen-associated molecular patterns (PAMPS) produced by pathogenic organisms that interact with pattern recognition receptors (i.e. TLRs) on fibroblasts. Cytokines (IL-13, IL-21, TGF-beta1), chemokines (MCP-1, MIP-1beta), angiogenic factors (VEGF), growth factors (PDGF), peroxisome proliferator-activated receptors (PPARs), acute phase proteins (SAP), caspases, and components of the renin-angiotensin-aldosterone system (ANG II) have been identified as important regulators of fibrosis and are being investigated as potential targets of antifibrotic drugs. This review explores our current understanding of the cellular and molecular mechanisms of fibrogenesis.

Immune mechanisms of corneal allograft rejection

Penetrating keratoplasty has been successfully performed on humans for over 100 years and remains the most common form of solid tissue transplantation. Although corneal allografts enjoy a remarkable degree of immune privilege, immune rejection remains the leading cause of keratoplasty failure. The immunologic basis for corneal allograft rejection was established in animal studies over 50 years ago, yet large gaps remain in our knowledge regarding the cellular and molecular mechanisms of corneal allograft rejection. The enormous redundancy in the mammalian immune system creates a condition that favors the development of multiple independent immune mechanisms that can produce corneal allograft rejection. Although there are few absolute principles, it is certain that the immune rejection of corneal allografts is (1) T cell-dependent, (1) heavily dependent upon CD4(+) T cells, (3) not restricted to either Th1 or Th2 T cell populations, and (4) dependent upon an intact repertoire of resident antigen presenting cells.

Prevention of acute and chronic allograft rejection with CD4+CD25+Foxp3+ regulatory T lymphocytes

A major challenge in transplantation medicine is controlling the very strong immune responses to foreign antigens that are responsible for graft rejection. Although immunosuppressive drugs efficiently inhibit acute graft rejection, a substantial proportion of patients suffer chronic rejection that ultimately leads to functional loss of the graft. Induction of immunological tolerance to transplants would avoid rejection and the need for lifelong treatment with immunosuppressive drugs. Tolerance to self-antigens is ensured naturally by several mechanisms; one major mechanism depends on the activity of regulatory T lymphocytes. Here we show that in mice treated with clinically acceptable levels of irradiation, regulatory CD4+CD25+Foxp3+ T cells stimulated in vitro with alloantigens induced long-term tolerance to bone marrow and subsequent skin and cardiac allografts. Regulatory T cells specific for directly presented donor antigens prevented only acute rejection, despite hematopoietic chimerism. By contrast, regulatory T cells specific for both directly and indirectly presented alloantigens prevented both acute and chronic rejection. Our findings demonstrate the potential of appropriately stimulated regulatory T cells for future cell-based therapeutic approaches to induce lifelong immunological tolerance to allogeneic transplants.

IL-5 up-regulates the expression of TGF-beta1 in human blood eosinophils in vitro

To investigate the effects of IL-5 on the expression of TGF-beta1 in eosinophils in vitro, eosinophils were incubated in the presence of the same concentrations of 1L-4, IL-5 and IFNgamma, different concentrations of IL-5 in vitro and changes of eosinophil viability were assessed by trypan blue exclusion. Non-cytokine was employed as a negative control. 16 h after the cultivation, supernatants and cells were assayed by using TGF-beta1 specific ELISA and RT-PCR. The mRNA expression and protein expresssion of TGF-beta1 in eosinophils stimulated with different cytokines was observed. The expression of TGF-beta1 protein in eosinophils was increased significantly by IL-4 (433.67 +/- 9.86 vs 228.9 +/- 2.87) and IL-5 (403.72 +/- 7.60 vs 228.9 +/- 2.87, P < 0.05), while decreased by IFNgamma (178.47 +/- 2.60 vs 228.9 +/- 2.87). At the same time, the results demonstrated that the basal level of TGF expression was enhanced by IL-5 in all samples (P < 0.05). The expression of TGF-beta1 mRNA was 1.42, 1.70, 1.76-folds higher than that of the non-stimulated controls. It is concluded that IL-5 can up-regulate the expression of TGF-beta1 in eosinophils in vitro, which might have effect in eosinophil-associated chronic rejection.

Loss of transgene following ex vivo gene transfer is associated with a dominant Th2 response: implications for cutaneous gene therapy

Host responses to therapeutic gene products are potentially serious complications in cutaneous gene therapy. Controlling immune responses to the therapeutic antigen may therefore be critical for an effective therapy. Both ex vivo and in vivo gene transfer to epidermal stem cells has been shown to induce transgene-specific immune responses; however, whether the mechanism of immune activation is the same is not clear. In this study, we have characterized transgene-specific immune responses in an ex vivo model of epidermal gene transfer using green fluorescent protein as a model antigen and retrovirus-mediated gene delivery. Contrary to T helper (Th)1-type responses induced following in vivo gene transfer to epidermis, rejection of ex vivo-transduced keratinocytes was associated with Th2/eosinophilc responses. These responses were characterized by interleukin (IL)-4 and IL-5 production by T cells, a predominance of anti-green fluorescent protein IgG1 in serum, the presence of numerous eosinophils within rejected skin, and a lack of class I-restricted cytotoxic T lymphocyte response. Pretreatment of mice receiving ex vivo transduced keratinocytes with neutralizing anti-IL-5 antibody prevented eosinophil infiltration and prolonged survival of transduced epidermis. These data indicate a role for the Th2/eosinophilic pathway in rejection of ex vivo-transduced keratinocytes, suggesting different requirements for achieving tolerance for ex vivo and in vivo approaches to gene therapy.

Immunological analogy between allograft rejection, recurrent abortion and pre-eclampsia - the same basic mechanism?

There are still controversies concerning the role of immunological mechanisms engaged both in recurrent abortions (RA) and pre-eclampsia (PE). According to some opinions, recurrent miscarriage is comparable to organ-specific autoimmune disease. Analysis of immune reactions shows that graft rejection shares many similar mechanisms with RA and PE. This fact allows us to conclude that rejection of transplanted alloantigenic organs and pregnancy loss have probably the same evolutionary origin. Subsets and functions of immunocompetent cells (T CD4, suppressor gammadeltaT, cytotoxic T CD8, Treg, Tr1, uterine NK cells), over-activation of innate immunity (activation of NK cytotoxic cells, macrophages, neutrophils and complement), changes of Th1/Th2 cytokine balance (IL-2, IL-12, IL-15, IL-18, IFNgamma, TNFalpha vs. IL-4, IL-10, TGFbeta), importance of HLA-G molecule, CD200/CD200R interaction, over-expression of adhesion molecules, fgl2 prothrombinase activation and stimulation of IDO and HO expression, all suggest that RA and PE are syndromes of fetal allograft rejection, and not organ-specific autoimmune diseases. According to that supposition, an analogy might exist between acute graft rejection and recurrent abortion, and between chronic graft rejection and pre-eclampsia.

Clopidogrel reduces the development of transplant arteriosclerosis

BACKGROUND

Transplant arteriosclerosis, the hallmark feature of chronic rejection, is still the major limiting factor for the long-term success of heart transplantation. Platelets have been implicated to play a role in the pathogenesis of this disease. Therefore the aim of this study was to investigate whether platelet inhibition alone has a positive effect on the development of transplant arteriosclerosis.

METHODS

Fully major histocompatibility complex-mismatched C57BL/6 (H2(b)) donor aortas were transplanted into CBA (H2(k)) recipients, and mice received different doses (1, 10, and 20 mg/kg) of clopidogrel or control saline as a daily intraperitoneal injection for 30 days. Blood was analyzed on days 2, 7, 14, and 30 by using a platelet aggregation test (adenosine diphosphate) for effectiveness of the treatment. Grafts were analyzed by means of histology and morphometry on day 30 after transplantation.

RESULTS

When mice were treated daily with 1 mg/kg clopidogrel in the absence of any other immunosuppression, transplant arteriosclerosis was significantly reduced compared with that seen in saline-treated control animals (intimal proliferation of 66% +/- 9% [1 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 7, P < or = .03). Daily application of 10 mg/kg and 20 mg/kg clopidogrel also significantly reduced the development of transplant arteriosclerosis compared with that seen in control animals (intimal proliferation of 61% +/- 11% [10 mg/kg clopidogrel] vs 54% +/- 10% [20 mg/kg clopidogrel] vs 77% +/- 5% [control], n = 8, P < or = .003). There was, however, no additional beneficial effect when compared with mice treated with 1 mg/kg clopidogrel (P = .06). Isografts did not show any signs of vascular lesions on day 30 after transplantation.

CONCLUSION

These results demonstrate that monotherapy with clopidogrel can effectively reduce the formation of transplant arteriosclerosis in a murine aortic allograft model.

CD8+ T-cell-mediated killing of donor dendritic cells prevents alloreactive T helper type-2 responses in vivo

Accumulating evidence indicates that, in absence of CD8+ T-cell activation, CD4+ T-cell-mediated allograft rejection is associated with a dominant Th2-cell response and eosinophil infiltrates. In this study, we analyzed the mechanisms by which CD8+ T cells regulate alloreactive CD4+ T-cell priming and differentiation into interleukin 4 (IL-4)-producing cells. We showed that interferon gamma (IFN-gamma) production by CD8+ T cells was dispensable for the inhibition of Th2-cell development, as well as tissue eosinophilia and type 2 cytokine production in the rejected grafts. Since we noticed that CD8+ T cells not only suppressed Th2 differentiation, but also down-modulated the overall priming of alloreactive CD4+ T cells, we evaluated whether CD8+ T cells act by limiting the accumulation of donor-derived dendritic cells (DCs) in lymph nodes. We found that indeed, alloreactive CD8+ T cells rapidly eliminated allogeneic DCs from T-cell areas of draining lymph nodes, through a perforin-dependent mechanism. Thus, our data demonstrate that cytotoxic T lymphocyte (CTL)-mediated clearance of allogeneic DCs is a negative feedback mechanism that limits the duration of alloantigen presentation in draining lymph nodes, thereby modulating the amplitude and polarization of the primary alloreactive CD4+ T-cell responses.

IL-4 deficiency prevents eosinophilic rejection and uncovers a role for neutrophils in the rejection of MHC class II disparate skin grafts

BACKGROUND

Acute rejection of MHC class II-disparate bm12 skin grafts by C57BL/6 recipient mice is characterized by massive graft infiltration by eosinophils, together with increased intragraft amounts of IL-4 and IL-5 mRNA. IL-5 blockade prevents the intragraft eosinophil infiltration and prolongs the survival of skin allografts. As the differentiation of T cell precursors into Th2 cells is largely driven by IL-4, we investigated the role of IL-4 in MHC class II-disparate allograft rejection.

METHODS

We performed skin grafts from MHC class II incompatible bm12 mice into wild-type C57BL/6 mice (IL-4) or C57BL/6 IL-4 deficient mice (IL-4). Graft survival, in vitro T cell reactivity, and histology were compared.

RESULTS

We observed that 50% of IL-4 mice rapidly rejected their bm12 allograft, whereas the other 50% retained their graft 60 days after transplantation. Histological examination of bm12 allografts retained by IL-4 mice showed a normal appearance with no inflammatory infiltrate and no eosinophils. Among IL-4 mice that acutely rejected their bm12 skin graft, we observed a dense polymorphonuclear infiltrate. The depletion of neutrophils significantly prolonged bm12 graft survival.

CONCLUSIONS

Eosinophil infiltrates, typical of MHC class II disparate acute skin graft rejection, are critically dependent on the availability of IL-4. IL-4 mice reject MHC class II disparate skin grafts by a pathway of rejection where neutrophils play a direct causal role.

Regulation of Fibrosis by the Immune System

Inflammation and fibrosis are two inter-related conditions with many overlapping mechanisms. Three specific cell types, macrophages, T helper cells, and myofibroblasts, each play important roles in regulating both processes. Following tissue injury, an inflammatory stimulus is often necessary to initiate tissue repair, where cytokines released from resident and infiltrating leukocytes stimulate proliferation and activation of myofibroblasts. However, in many cases this drive stimulates an inappropriate pro-fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro-inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Moreover, inflammatory cells have been shown to play contradictory roles in initiation, amplification, and resolution of fibrotic disease processes. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to be fully appreciated. In the following review, we discuss the fibrotic disease process from the context of the immune response to injury. We review the major cellular and soluble factors controlling these responses and suggest ways in which more specific and, hopefully, more effective therapies may be derived.

Regulatory Role of Host CD8+ T Lymphocytes in Experimental Graft-versus-Host Disease across a Single Major Histocompatibility Complex Class II Incompatibility

BACKGROUND

CD8+ T cells are known to regulate type 2 helper T cell (Th2) alloreactive immune responses but their mode of activation is unclear. We investigated the role of host CD8+ T cells in experimental Th2-type graft-versus-host disease (GVHD) where donor/recipient disparity is restricted to a single major histocompatibility complex (MHC) class II antigen.

METHODS

Immunoglobulin (Ig) E serum levels, eosinophilia and lymphoid tissue hyperplasia were compared after injection of bm12 CD4+ T cells in either wild-type or CD8+ T cell-deficient (CD8-/-) C57BL/6 mice. In vitro, we explored effects of the addition of CD8+ T cells from wild-type or IFN-gamma-/- mice in mixed leukocyte cultures prepared with beta2 microglobulin-deficient (beta2m-/-) CD4+ T cells as responders or beta2m dendritic cells as stimulators.

RESULTS

HyperIgE resolved after 3 weeks in wild-type hosts whereas it persisted for 6 weeks in CD8-/- hosts. Eosinophil infiltrates in lymph nodes were significantly enhanced in CD8-/- hosts. Increased serum levels of IL-5 and IL-13 in CD8-/- hosts confirmed the enhancement of Th2-type responses in the context of recipient CD8+ T cell deficiency. Hyperplasia of lymph nodes and spleen were similar in both groups, as well as in vivo proliferation of donor CD4+ T cells. In vitro, CD8+ T cell regulation of the alloreactive Th2 response depended on their production of IFN-gamma and did not require expression of beta2m on CD4+ T cells or antigen-presenting cells.

CONCLUSIONS

Host CD8+ T cells regulate alloreactive Th2 responses during graft-versus-host disease through an IFN-gamma dependent pathway, independently of the recognition of beta2m-associated MHC class I molecules.

Cutting edge: atopy promotes Th2 responses to alloantigens and increases the incidence and tempo of corneal allograft rejection

A large body of evidence suggests that corneal allograft rejection is mediated by a type 1 Th cell response and that deviation toward type 2 immunity favors graft survival. However, clinical observations indicate that patients with severe ocular allergies have increased risk of corneal allograft rejection. We used a mouse model of atopic conjunctivitis to evaluate the effects of Th2 immune deviation on corneal allograft survival and possible mechanisms of graft rejection. Our results reveal the following novel findings: 1) atopic conjunctivitis promotes systemic Th2 immune responses to corneal graft donor alloantigens; 2) corneal allografts in atopic host eyes have an increased incidence and swifter tempo of rejection; 3) increased rejection is associated with alterations in systemic T cell-mediated responses to donor alloantigens; and 4) corneal allograft rejection in atopic hosts does not require the direct involvement of infiltrating eosinophils.