Analysis of the Th1/Th2 paradigm in transplantation: interferon-gamma deficiency converts Th1-type proislet allograft rejection to a Th2-type xenograft-like response

Roles of IL-33 in the Pathogenesis of Cardiac Disorders

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family and is believed to play important roles in different diseases by binding to its specific receptor suppression of tumorigenicity 2 (ST2). In the heart, IL-33 is expressed in different cells including cardiomyocytes, fibroblasts, endothelium, and epithelium. Although many studies have been devoted to investigating the effects of IL-33 on heart diseases, its roles in myocardial injuries remain obscure, and thus further studies are mandatory to unravel the underlying molecular mechanisms. We highlighted the current knowledge of the molecular and cellular characteristics of IL-33 and then summarized its major roles in different myocardial injuries, mainly focusing on infection, heart transplantation, coronary atherosclerosis, myocardial infarction, and diabetic cardiomyopathy. This narrative review will summarize current understanding and insights regarding the implications of IL-33 in cardiac diseases and its diagnostic and therapeutic potential for cardiac disease management.

Multiple Injections of Adipose-Derived Stem Cells Improve Graft Survival in Human-to-Rat Skin Xenotransplantation through Immune Modulation

BACKGROUND

Adipose-derived stem cells (ADSCs) exert immunomodulatory effects in the treatment of transplant rejection. This study aimed to evaluate the effects of ADSCs on the skin graft survival in a human-to-rat xenograft transplantation model and to compare single and multiple injections of ADSCs.

METHODS

Full-thickness human skin xenografts were transplanted into the backs of Sprague-Dawley rats. The rats were injected subcutaneously on postoperative days 0, 3, and 5. The injections were as follows: triple injections of phosphate-buffered saline (PBS group), a single injection of ADSCs and double injections of PBS (ADSC × 1 group), and triple injections of ADSCs (ADSC × 3 group). The immunomodulatory effects of ADSCs on human skin xenografts were assessed.

RESULTS

Triple injections of ADSCs considerably delayed cell-mediated xenograft rejection compared with the PBS and ADSC × 1 groups. The vascularization and collagen type 1-3 ratios in the ADSC × 3 group were significantly higher than those in the other groups. In addition, intragraft infiltration of CD3-, CD4-, CD8-, and CD68-positive cells was reduced in the ADSC × 3 group. Furthermore, in the ADSC × 3 group, the expression levels of proinflammatory cytokine interferon-gamma (IFN-γ) were decreased and immunosuppressive prostaglandin E synthase (PGES) was increased in the xenograft and lymph node samples.

CONCLUSION

This study presented that triple injections of ADSCs appeared to be superior to a single injection in suppressing cell-mediated xenograft rejection. The immunomodulatory effects of ADSCs are associated with the downregulation of IFN-γ and upregulation of PGES in skin xenografts and lymph nodes.

High-resolution phenotyping of early acute rejection reveals a conserved alloimmune signature

Alloimmune responses in acute rejection are complex, involving multiple interacting cell types and pathways. Deep profiling of these cell types has been limited by technology that lacks the capacity to resolve this high dimensionality. Single-cell mass cytometry is used to characterize the alloimmune response in early acute rejection, measuring 37 parameters simultaneously, across multiple time points in two models: a murine cardiac and vascularized composite allotransplant (VCA). Semi-supervised hierarchical clustering is used to group related cell types defined by combinatorial expression of surface and intracellular proteins, along with markers of effector function and activation. This expression profile is mapped to visualize changes in antigen composition across cell types, revealing phenotypic signatures in alloimmune T cells, natural killer (NK) cells, and myeloid subsets that are conserved and that firmly distinguish rejecting from non-rejecting grafts. These data provide a comprehensive, high-dimensional profile of cellular rejection after allograft transplantation.

Double deficiency for RORγt and T-bet drives Th2-mediated allograft rejection in mice

Although Th1, Th2, and Th17 cells are thought to be major effector cells in adaptive alloimmune responses, their respective contribution to allograft rejection remains unclear. To precisely address this, we used mice genetically modified for the Th1 and Th17 hallmark transcription factors T-bet and RORγt, respectively, which allowed us to study the alloreactive role of each subset in an experimental transplant setting. We found that in a fully mismatched heterotopic mouse heart transplantation model, T cells deficient for T-bet (prone to Th17 differentiation) versus RORγt (prone to Th1 differentiation) rejected allografts at a more accelerated rate, indicating a predominance of Th17- over Th1-driven alloimmunity. Importantly, T cells doubly deficient for both T-bet and RORγt differentiated into alloreactive GATA-3-expressing Th2 cells, which promptly induced allograft rejection characterized by a Th2-type intragraft expression profile and eosinophilic infiltration. Mechanistically, Th2-mediated allograft rejection was contingent on IL-4, as its neutralization significantly prolonged allograft survival by reducing intragraft expression of Th2 effector molecules and eosinophilic allograft infiltration. Moreover, under IL-4 neutralizing conditions, alloreactive double-deficient T cells upregulated Eomesodermin (Eomes) and IFN-γ, but not GATA-3. Thus, in the absence of T-bet and RORγt, Eomes may salvage Th1-mediated alloimmunity that underlies IL-4 neutralization-resistant allograft rejection. We summarize that, whereas Th17 cells predictably promote allograft rejection, IL-4-producing GATA-3(+) Th2 cells, which are generally thought to protect allogeneic transplants, may actually be potent facilitators of organ transplant rejection in the absence of T-bet and RORγt. Moreover, Eomes may rescue Th1-mediated allograft rejection in the absence of IL-4, T-bet, and RORγt.

Roles of Islet Toll-Like Receptors in Pig to Mouse Islet Xenotransplantation

Although innate immunity plays important roles in xenograft rejection, there have been few studies on the role of toll-like receptors (TLRs) in xenotransplantation. Furthermore, most studies focused on the recipient's TLRs. Therefore, we investigated whether TLRs in porcine islets can contribute to islet xenograft rejection. Adult porcine islets were isolated and stimulated by polyinosinic/polycytidylic acid (poly I:C) or lipopolysaccharide (LPS). Both poly I:C and LPS stimulation in porcine islets induced expression of chemokines (RANTES, MCP-1, IP-10, and IL-8), cytokines (IL-6 and type I interferons), and adhesion molecules (VCAM-1 and ICAM-1). Porcine islet supernatants stimulated by TLR agonists induced chemotaxis of human leukocytes. They also induced procoagulant activation (tissue factor and fgl-2). However, TLR stimulation did not influence insulin secretion. When porcine MyD88 was knocked down using shRNA lentivirus, TLR-mediated induction of proinflammatory mediators and procoagulants was attenuated. When LPS was injected to MyD88 or TLR4 knockout mice after porcine islet transplantation, LPS stimulation on donor islets interfered with islet xenograft tolerance induction by anti-CD154 antibodies. Inflammatory cell infiltration and expression of proinflammatory chemokines and cytokines in islet xenografts also increased. In conclusion, TLR activation in porcine islets induced both a proinflammatory and procoagulant response and thereby contributed to xenograft rejection.

B7-H4 induces donor-specific tolerance in mouse islet allografts

Negative cosignaling molecules play an important role in regulating T-cell responses to alloantigen stimulation. We recently reported that adenoviral-mediated transduction of islet allografts with B7-H4 inhibits allograft rejection. In this study, we investigate the mechanism for B7-H4-induced prolongation of mouse islet allograft survival. Streptozotocin-induced diabetic C57BL/6 mice were rendered normoglycemic by renal subcapsular implants of B7-H4-transduced BALB/c islets. Grafts and spleens were removed after days 2, 10, and 60 (n = 8 each) for characterization of kinetics of Foxp3 and interleukin 10 (IL-10) expression. Mixed lymphocyte reaction (MLR) was done at day 60. Ten mice were subjected to nephrectomy at 60 days and then five were implanted with secondary BALB/c islets and five were given third-party CBA/J islets. An increase in Foxp3 and IL-10 mRNA expression was detected in recipients' spleens at day 60 and this was associated with increased quantities of Foxp3(+) cells. Splenocytes at day 60 showed hyporesponsiveness during MLR to alloantigen stimulation. Proliferation was partially restored after CD25(+) T-cell depletion. Secondary BALB/c islets survived for 79 ± 29 days compared with 21 ± 3.6 days for CBA/J islets (p < 0.001). Local expression of B7-H4 induces long-term unresponsiveness to donor-specific alloantigens, and is associated with T regulatory cells, suggesting the development of tolerance.

Quantitative in situ analysis of FoxP3+ T regulatory cells on transplant tissue using laser scanning cytometry

There is abundant evidence that immune cells infiltrating into a transplanted organ play a critical role for destructive inflammatory or regulatory immune reactions. Quantitative in situ analysis (i.e., in tissue sections) of immune cells remains challenging due to a lack of objective methodology. Laser scanning cytometry (LSC) is an imaging-based methodology that performs quantitative measurements on fluorescently and/ or chromatically stained tissue or cellular specimens at a single-cell level. In this study, we have developed a novel objective method for analysis of immune cells, including Foxp3(+) T regulatory cells (Tregs), on formalin-fixed /paraffin-embedded (FFPE) transplant biopsy sections using iCys® Research Imaging Cytometer. The development of multiple immunofluorescent staining was established using FFPE human tonsil sample. The CD4/CD8 ratio and the population of Tregs among CD4(+) cells were analyzed using iCys and compared with the results from conventional flow cytometry analysis (FCM). Our multiple immunofluorescent staining techniques allow obtaining clear staining on FFPE sections. The CD4/CD8 ratio analyzed by iCys was concordant with those obtained by FCM. This method was also applicable for liver, small intestine, kidney, pancreas, and heart transplant biopsy sections and provide an objective quantification of Tregs within the grafts.

Eosinophils in health and disease: the LIAR hypothesis

Discussions of eosinophils are often descriptions of end-stage effector cells with destructive capabilities mediated predominantly by released cytotoxic cationic granule proteins. Moreover, eosinophils in the medical literature are invariably associated with the pathologies linked with helminth infections or allergic diseases such as asthma. This has led to an almost fatalist view of eosinophil effector functions and associated therapeutic strategies targeting these cells that would make even William of Ockham proud - eosinophil effector functions have physiological consequences that increase patient morbidity/mortality and 'the only good eosinophils are dead eosinophils'. Unfortunately, the strengths of dogmas are also their greatest weaknesses. Namely, while the repetitive proclamation of dogmatic concepts by authoritative sources (i.e. reviews, meeting proceedings, textbooks, etc.) builds consensus within the medical community and lower the entropies surrounding difficult issues, they often ignore not easily explained details and place diminished importance on alternative hypotheses. The goal of this perspective is twofold: (i) we will review recent observations regarding eosinophils and their activities as well as reinterpret earlier data as part of the synthesis of a new paradigm. In this paradigm, we hypothesize that eosinophils accumulate at unique sites in response to cell turnover or in response to local stem cell activity(ies). We further suggest that this accumulation is part of one or more mechanisms regulating tissue homeostasis. Specifically, instead of immune cells exclusively mediating innate host defence, we suggest that accumulating tissue eosinophils are actually regulators of Local Immunity And/or Remodeling/Repair in both health and disease - the LIAR hypothesis; (ii) we want to be inflammatory (pun intended!) and challenge the currently common perspective of eosinophils as destructive end-stage effector cells. Our hope is to create more questions than we answer and provoke everyone to spend countless hours simply to prove us wrong!

Completely mismatched allogeneic CD3/CD28 cross-linked Th1 memory cells elicit anti-leukemia effects in unconditioned hosts without GVHD toxicity

Fully allogeneic CD3/CD28 cross-linked Th1 cells were found to elicit host-mediated anti-leukemia effects without GVHD toxicity. Mice inoculated with a lethal dose of BCL1 leukemia demonstrated significantly enhanced survival after allogeneic Th1 treatment. Cure rates of 12.5% with a single allogeneic cell infusion and 31.25% with multiple infusions were demonstrated. Cured mice were able to reject rechallenge with a lethal dose of tumor without further treatment. These results suggest that use of intentionally mis-matched, Th1 memory cells infused with cross-linked CD3/CD28 could represent a novel clinical approach to eliciting potent anti-tumor effects in patients without conditioning and without GVHD toxicity.

Mapping immune response profiles: the emerging scenario from helminth immunology

Metazoan parasites of mammals (helminths) belong to highly divergent animal groups and yet induce a stereotypical host response: Th2-type immunity. It has long been debated whether this response benefits the host or the parasite. We review the current literature and suggest that Th2 immunity is an evolutionarily appropriate response to metazoan invaders both in terms of controlling parasites and repairing the damage they inflict. However, successful parasites induce regulatory responses, which become superimposed with, and control, Th2 responses. Beyond helminth infection, this superimposition of response profiles may be the norm: both Th1 and Th2 responses coexist with regulatory responses or, on the contrary, with the inflammatory Th17 responses. Thus, typical responses to helminth infections may differ from Th2-dominated allergic reactions in featuring not only a stronger regulatory component but also a weaker Th17 component. The similarity of immune response profiles to phylogenetically distinct helminths probably arises from mammalian evolution having hard-wired diverse worm molecules, plus tissue-damage signals, to the beneficial Th2 response, and from the convergent evolution of different helminths to elicit regulatory responses. We speculate that initiation of both Th2 and regulatory responses involves combinatorial signaling, whereby TLR-mediated signals are modulated by signals from other innate receptors, including lectins.

Matrix adherence of endothelial cells attenuates immune reactivity: induction of hyporesponsiveness in allo‐ and xenogeneic models

Endothelial integrity regulates vascular tone, luminal patency, and the immune reactivity to tissue grafts. Endothelial dysfunction is the first marker and site of disease initiation and severity. It has long been known that endothelial biochemical function is density dependent, and we have recently shown that endothelial immunobiology is anchorage dependent. Matrix-embedded endothelial cells (EC) establish a controlled anchorage state and are not only immune protected but also induce a system immune protective state. We now define this aspect of vascular and immune biology in detail. The in vitro immune response of allogeneic splenocytes (proliferation, lytic activity, and cytokine expression) on exposure to aortic EC was significantly reduced if EC were embedded within three-dimensional collagen matrices (3D-EC; P<0.005) to an even greater extent than EC that had reached confluence as monolayers on tissue culture plates (EC-TCPS). Splenocyte reactivity was enhanced with repeated exposure to EC-TCPS but minimally if preexposed to 3D-EC (P<0.002). 3D-EC induced significantly greater differentiation of splenocytes into CD4+ CD25+ Foxp3+ regulatory T cells than EC-TCPS (P<0.02). The reduced response to 3D-EC and potential protective effect to subsequent exposure were confirmed in vivo. Repeated exposure of immune-competent mice to injections of xenogeneic EC-TCPS induced vigorous host immunity. In contrast, prior implantation of 3D-EC induced hyporesponsiveness toward subsequent injection of EC-TCPS with reduced humoral response, decreased lytic activity, and lower frequency of effector splenocytes (P<0.001). EC interaction with its matrix determines phenotype, viability, and biosecretory potential. We now show that this microenvironmental interaction also influences endothelial-mediated activation of allo- and xenogeneic immune cells. 3D matrix-embedding limits the ability of EC to initiate adaptive immunity, and initial exposure to 3D-EC confers hyporesponsiveness to subsequent exposure to immunogeneic EC. These effects transcended the traditional control that confluence imposes on EC and reflects perhaps even higher order control. Our findings might offer novel insights to endothelial-mediated diseases and potential cell-based therapies.

Cell-matrix contact prevents recognition and damage of endothelial cells in states of heightened immunity

BACKGROUND

Autoimmunity may exacerbate vascular disease, particularly in the form of anti-endothelial cell (EC) antibodies. The increased morbidity of cardiovascular diseases in concert with diabetes mellitus, hypertension, and other systemic illnesses may reflect the increase presence and potency of these antibodies. Matrix-embedded ECs act as powerful regulators of vascular repair accompanied by significant reduction in expected systemic and local inflammation. We compared the immune response against free and matrix-embedded ECs in naïve mice and mice with heightened EC immune reactivity.

METHODS AND RESULTS

Mice were presensitized to EC with repeated (days 0, 21, 35) subcutaneous injections of saline-suspended porcine EC (PAE) (5 x 10(5) cells). Controls received saline injections. On day 42, mice received 5 x 10(5) matrix-embedded or free PAEs. Circulating PAE-specific antibodies and effector T-cells were analyzed via flow cytometry, and xenoreactive lymphocytes via ELISPOT, 90 days after implantation. PAE-specific antibody-titers, frequency of CD4+-effector cells, and xenoreactive splenocytes were 2- to 4-fold lower (P<0.0001) when naïve mice were injected with matrix-embedded instead of saline-suspended PAEs. Though basal levels of circulating antibodies were significantly elevated after serial PAE injections (2210+/-341 mean fluorescence intensity, day 42) and almost doubled again 90 days after injection of a fourth set of free PAEs, antibody levels declined by half in recipients of matrix-embedded PAEs at day 42 (P<0.0001). Levels of CD4+-effector cells and xenoreactive splenocytes showed similar results.

CONCLUSIONS

Implantation of free PAE elicits a significant immune response in naïve mice and even more pronounced in mice with predeveloped anti-endothelial immunity. Matrix-embedding protects xenogeneic ECs against immune reaction in naïve mice and to a similar extent in mice with heightened immune reactivity. Matrix-embedded EC might offer a promising approach for treatment of advanced cardiovascular disease.

Evidence that T-Helper Type 2 Cell-Derived Cytokines and Eosinophils Contribute to Acute Rejection of Orthotopic Corneal Xenografts in Mice

BACKGROUND

Because guinea pig corneal xenografts are rejected acutely (within 16 days) in mouse eyes by a T-cell-dependent mechanism, the authors wished to determine the functional phenotype of CD4+ effector T cells.

METHODS

Orthotopic corneal xenotransplantation was performed from strain 13 guinea pigs to BALB/c mice. Grafted eyes were removed at specified times and examined histologically or subjected to cytokine and chemokine mRNA analysis using a multi-probe ribonuclease protection assay. Draining cervical lymph node cells were harvested at specified times and stimulated in vitro with x-irradiated strain 13 guinea pig spleen cells. Supernatants were assayed by enzyme-linked immunosorbent assay for content of interleukin (IL)-2, interferon (IFN)-gamma, IL-4, IL-5, and IL-10 and cells were used for mRNA analysis.

RESULTS

Rejected corneal xenografts were heavily infiltrated with polymorphonuclear leukocytes, the majority of which were eosinophils. These eyes contained mRNA for IL-4, IL-6, IL-10, IL-13, IL-15, and IFN-gamma. When stimulated with guinea pig spleen cells, T cells from draining cervical lymph nodes secreted primarily IL-4, IL-5, IL-10, and IFN-gamma. Eotaxin was overexpressed in eyes with rejected corneal xenografts.

CONCLUSIONS

Acute rejection of corneal xenografts in mice is mediated by T cells that display a mixed T-helper (Th) type 2/Th1 phenotype and secrete eotaxin, an eosinophil chemoattractant. Eosinophil-dependent xenograft rejection bears similarities to immune elimination of parasites.

The contribution of chemokines and chemokine receptors to the rejection of fetal proislet allografts

Chemokines regulate the recruitment of leukocytes to sites of inflammation and may therefore play an important role in lymphocyte trafficking between draining lymph nodes and pancreatic islet tissue allografts. The intragraft expression of alpha- and beta-chemokine mRNA during the rejection of BALB/c proislet (fetal precursor islet tissue) allografts in CBA/H mice was assessed quantitatively and semiquantitatively by RT-PCR analyses. Allograft rejection was associated with the strongly enhanced (from day 4) and prolonged expression (up to day 10) of the alpha-chemokine IP-10 and enhanced intragraft mRNA expression of the beta-chemokines MCP-1, MIP-lalpha, MIP-1beta, RANTES, and eotaxin. Peak transcript expression was identified at day 4 (IP-10, MCP-1), day 5 (eotaxin), day 6 (MIP-1alpha, MIP-1beta), and day 14 (RANTES). To examine the role of beta-chemokine receptors in allograft rejection, additional allografts to CCR2-/- , CCR5-/-, and wild-type CCR+/+ mice were analyzed by histology, immunohistochemistry, and morphometry. In CCR5-/- mice, the intragraft recruitment of T cells and macrophages was slower and allograft destruction was delayed; in CCR2-/- mice, the initial entry of macrophages was retarded but graft survival was not prolonged. These findings suggest that IP-10 regulates the initial influx of T cells into proislet allografts, MCP-1/CCR2 signaling controls initial macrophage entry, and the MIP-1alpha, MIP-1beta, and RANTES/CCR5 pathway contributes to the rejection response by subsequently amplifying the recruitment of T cell subpopulations required for graft destruction.

Inhibition of cellular immune responses to encapsulated porcine islet xenografts by simultaneous blockade of two different costimulatory pathways

BACKGROUND

Transplantation of human islets has been successful clinically. Since human islets are scarce, we are studying microencapsulated porcine islet xenografts in nonobese diabetic (NOD) mice. We have evaluated the cellular immune response in NOD mice with and without dual costimulatory blockade.

METHODS

Alginate-poly-L-lysine-encapsulated adult porcine islets were transplanted i.p. in untreated diabetic NODs and NODs treated with CTLA4-Ig to block CD28/B7 and with anti-CD154 mAb to inhibit CD40/CD40-ligand interactions. Groups of mice were sacrificed on subsequent days; microcapsules were evaluated by histology; peritoneal cells were analyzed by FACS; and peritoneal cytokines were quantified by ELISA. Controls included immunoincompetent NOD-Scids and diabetic NODs given sham surgery or empty microcapsules.

RESULTS

Within 20 days, encapsulated porcine islets induced accumulation of large numbers of macrophages, eosinophils, and significant numbers of CD4 and CD8 T cells at the graft site, and all grafts were rejected. During rejection, IFNgamma, IL-12 and IL-5 were significantly elevated over sham-operated controls, whereas IL-2, TNFalpha, IL-4, IL-6, IL-10, IL-1beta and TGFbeta were unchanged. Treatment with CTLA4-Ig and anti-CD154 prevented graft destruction in all animals during the 26 days of the experiment, dramatically inhibited recruitment of host inflammatory cells, and inhibited peritoneal IFNgamma and IL-5 concentrations while delaying IL-12 production.

CONCLUSIONS

When two different pathways of T cell costimulation were blocked, T cell-dependent inflammatory responses were inhibited, and survival of encapsulated islet xenografts was significantly prolonged. These findings suggest synergy between encapsulation of donor islets and simultaneous blockade of two host costimulatory pathways in prolonging xenoislet transplant survival.

Predominant expression of Th2 cytokines and interferon-gamma in xenogeneic cardiac grafts undergoing acute vascular rejection

BACKGROUND

The Th1 response has been shown to play a role in acute allograft rejection, whereas the Th2 response has been implicated in the protection of allografts. Unlike allografts, the pattern of cytokines in response to solid-organ xenografts has been the subject of limited studies. We investigated intragraft cytokine expression in a concordant cardiac xenograft model (rat-to-mouse) to test if a particular cytokine profile predominates.

METHODS

Intra-abdominal cardiac transplantation was performed using C57BL/10 mice as recipients of PVG.R8 rat hearts. Syngeneic grafts (C57BL/10-to-C75BL/10) served as controls. Cardiac grafts harvested on various days posttransplantation were analyzed for histology and intragraft cytokine expression using reverse-transcriptase polymerase chain reaction.

RESULTS

The grafts in this model were rejected with a mean survival time of 7+/-1 days and showed extensive evidence of acute vascular rejection, consisting of global distortion of myocardial architecture, fewer cellular infiltrates, interstitial hemorrhage with myocyte necrosis thrombosis, and vasculitis with neutrophils and lymphocytes infiltrating vessel walls. Cardiac xenografts predominantly expressed Th2 cytokines, interleukin (IL)-4, IL-10, and transforming growth factor-beta with various kinetics. IL-10 was detectable on day 1 and reached its peak level of expression on day 6 posttransplantation. IL-4 showed minimal and undetectable expression on days 1 and 3 and significant expression on day 6 posttransplantation. Transforming growth factor-beta was expressed moderately on all days examined. The expression of interferon (IFN)-gamma, a Th1 cytokine, was specific to xenografts and showed a gradual increase from days 3 to 6 posttransplantation. In marked contrast, IL-2 showed complete lack of expression.

CONCLUSIONS

Our data demonstrate predominant expression of Th2 cytokines and IFN-gamma in cardiac xenografts undergoing acute vascular rejection. The Th2 cytokines may promote acute vascular rejection by regulating the humoral response, and IFN-gamma may delay, but not prevent, this response.

Islet transplantation in the discordant tilapia-to-mouse model: a novel application of alginate microencapsulation in the study of xenograft rejection

BACKGROUND

Tilapia islet xenograft rejection is characterized by infiltration with macrophages (Mphis), eosinophils (Ephis), and T lymphocytes. The presence of these cells indicates they contribute to rejection; therefore, an attempt was made to assess their role through host immunomodulation.

METHODS

Tilapia islet cells were transplanted under the kidney capsule of streptozotocin diabetic Balb/c mice, which were then treated with one of several immunomodulatory regimes targeting Mphis, Ephis, or T cells. Mphis were depleted using either silica or liposome-entrapped Cl2MDP. Ephi migration was blocked using monoclonal antibodies (mAbs) targeting interleukin (IL)-4 or IL-5. T-cell function was altered with mAbs targeting CD3, CD4, or CD8. Finally, T helper (Th)1 and Th2 activity was altered by depleting essential Th1 or Th2 cytokines with mAbs or by promoting a Th1 response with the injection of exogenous IL-12. The effects of antibody-mediated immunomodulation on graft survival were initially screened by cotransplanting alginate-encapsulated, mAb-secreting hybridoma cells into the peritoneal cavity at the time of islet transplantation. Significant prolongation was then confirmed using purified antibodies injected at the time of islet transplantation. Rejected grafts were examined histologically, and immunohistochemistry was used to assess the cellular infiltrates for each of the treatment groups.

RESULTS

Modulation of Mphis and Ephis alone did not significantly delay functional rejection of tilapia islet grafts (maximal mean graft survival time [mGST]=7.1+/-1.7 and 9.4+/-3.4, respectively) compared with untreated controls (mGST=8.2+/-1.0). Treatment of transplanted animals with antibodies against CD3 or CD4 significantly promoted graft survival (maximal mGST=16.3+/-5.8 and 34.0+/-11.6, respectively), whereas targeting CD8 and Th1 and Th2 cytokines showed no prolonging effect (maximal mGST=7.8+/-2.9 and 9.5+/-4.3, respectively).

CONCLUSION

Our results indicate that rejection in the tilapia-to-mouse model follows a pattern similar to other models of discordant islet cell xenotransplantation.

T cell-activated macrophages are capable of both recognition and rejection of pancreatic islet xenografts

Macrophages have been proposed as the major effector cell in T cell-mediated xenograft rejection. To determine their role in this response, NOD-SCID mice were transplanted with fetal pig pancreas (FPP) before reconstitution with CD4(+) T cells from BALB/c mice. Twelve days after CD4(+) T cell reconstitution, purified macrophages (depleted of T cells) were isolated from CD4(+) T cell-reconstituted FPP recipient mice and adoptively transferred to their nonreconstituted counterparts. After adoptive macrophage transfer, FPP recipient mice transferred with macrophages from CD4(+) T cell-reconstituted mice demonstrated xenograft destruction along with massive macrophage infiltration at day 4 and complete graft destruction at day 8 postmacrophage transfer. By contrast, FPP recipients that received macrophages from nonreconstituted mice showed intact FPP xenografts with few infiltrating macrophages at both days 4 and 8 after macrophage transfer. The graft-infiltrating macrophages showed increased expression of their activation markers. Depletion of endogenous macrophages or any remaining CD4(+) T cells did not delay graft rejection in the macrophage-transferred FPP recipients, whereas depletion of transferred macrophages with clodronate liposomes prevented graft rejection. Our results show that macrophages primed by FPP and activated by CD4(+) T cells were attracted from the peripheral circulation and were capable of specific targeting and destruction of FPP xenografts. This suggests that in xenograft rejection, there are macrophage-specific recognition and targeting signals that are independent of those received by T cells.

Role of CD4+ and CD8+ T cells in the rejection of concordant pancreas xenografts

BACKGROUND

We studied the ability of CD4 and CD8 T cells to induce rejection of pancreas xenografts in a concordant combination using rat pancreas xenografts as donors and chemically induced diabetic mice as recipients.

METHODS

Lewis rat (2 to 3 weeks old) pancreas xenografts were transplanted into streptozotocin (STZ)-induced diabetic mice. Lymphocyte proliferation and cytokine production were analyzed in vitro. All pancreas xenografts were assessed by functional (blood glucose) and histopathologic examinations.

RESULTS

Lewis rat pancreas grafts were rejected within 10 to 13 days, with mononuclear cell infiltrate and tissue necrosis in STZ-induced diabetic mice. A predominant T cell receptor alphabeta -CD4 cell (on day 4) and T cell receptor alphabeta -CD8 cell (on day 8) infiltrate and IgM deposition were found in the pancreas xenografts after transplantation. Anti-CD4 (GK1.5), but not anti-CD8 (YTS169.4), monoclonal antibodies resulted in a prolonged survival of Lewis rat pancreas xenografts. Lewis pancreas xenografts were permanently accepted by CD4 knockout mice but not by CD8 knockout mice. The pancreas xenografts were acutely rejected with a mean survival time of 15.3 days in B cell-deficient mice (microMT/microMT). Transfer of CD4 but not CD8 spleen cells from naïve C57BL/6 mice into Rag2 mice led to acute rejection of transplanted pancreas xenografts. However, activated CD8 spleen cells elicited rejection of Lewis rat pancreas xenografts in SZT-induced diabetic mice.

CONCLUSION

The current results show that CD4 T cells are necessary and sufficient for mediating the rejection of Lewis rat pancreas xenografts in STZ-induced diabetic mice. However, CD8 cells, when activated, can also induce acute rejection of concordant pancreas xenografts.

Acute xenograft rejection mediated by antibodies produced independently of TH1/TH2 cytokine profiles

There is substantial support for the hypothesis that T(H)1 cytokine responses are critical for the normal elaboration of allograft rejection. Recent studies by Wang et al. (1) underscore the importance of T(H)2 responses in xenograft rejection and revealed that T(H)1 cytokines, IL-12 and interferon-gamma (IFN-gamma), can negatively regulate the development of humoral responses necessary for xenograft rejection. Their exceptional studies prompted us to test whether the ability of allografts to elicit cellular rejection and xenografts to induce humoral rejection also result from the differential ability to induce T(H)1 and T(H)2 responses. We compared the kinetics of antibody and cytokine (IFN-gamma and IL-4) production in C57BL/6 mice following allograft transplantation with BALB/c hearts and in C57BL/6 and BALB/c mice following transplantation with Lewis rat hearts. We also compared the ability of BALB/c mice, deficient in the ability to produce IL-4 or IFN-gamma, to reject xenografts and produce xenoantibodies. We observed that T(H)1/T(H)2 cytokine production minimally affected the kinetics of graft rejection but regulated the magnitude of IgG subclass production. Anti-graft IgM played a critical role in initiating acute antibody-mediated xenograft rejection, and the production antigraft IgM was unaffected by IL-4 or IFN-gamma deficiency. In contrast to the report by Wang et al. (1), we conclude that antibody-mediated xenograft rejection in the concordant Lewis rat heart-to-C57BL/6 mouse xenotransplantation model is dependent on anti-IgM production but independent of T(H) cytokine profiles.

IFN-gamma but not IL-4 is important for mouse CD4+ T cell-mediated macrophage activation following their exposure to pig cells in vitro

In order to investigate the mechanism by which CD4+ T cells and macrophages interact in the xenogeneic immune response, murine CD4+ T cells and macrophages were used as responder cells in culture with irradiated fetal pig spleen cells (FPSC) as pig xenogeneic stimulators. In this in vitro model, murine CD4+ T cells and macrophages were cultured individually, or together with FPSC. In addition, mouse CD4+ T cells were also cultured with autologous macrophages which were previously stimulated by FPSC. The cultured murine cells were analyzed for expression of CD4+ T cell and macrophage activation markers (cell surface markers and cytokines) as well as cytokine production. CD4+ T cells and macrophages cultured alone or together without FPSC showed unchanged low levels of expression of activation markers. Coculture of macrophages with FPSC and in the absence of CD4+ T cells induced increased expression levels of all the activation markers examined except B7.2 and ICAM-1. Addition of CD4+ T cells to the coculture further enhanced this up-regulation. Coculture of CD4+ T cells with FPSC-stimulated macrophages, but not naive macrophages, or FPSC alone, resulted in significantly increased numbers of CD4+ T cells coexpressing their activation markers, especially IFN-gamma and CD40L, and this expression was enhanced further by including FPSC in the coculture. The activation of both CD4+ T cells and macrophages in their coculture with FPSC was suppressed by neutralizing IFN-gamma but not IL-4. Our results demonstrated that interaction of CD4+ T cells and autologous macrophages was required for their optimal activation in response to pig xenogeneic stimulation. The mechanisms involved included cell-cell and/or cytokine interactions, and in particular IFN-gamma mediated communication was involved. Macrophages activated by pig cells in the absence of CD4+ T cells were able to activate naive CD4+ T cells, thus providing an important communication pathway between innate immune activation and a T cell mediated response in xenograft rejection.

Islet xenograft rejection in absence of CD8+ T cells does not require either interferon-gamma or interleukin-5

We recently demonstrated that interleukin-5 and eosinophils mediate rejection of skin allografts when CD8+ T cell-dependent and Th1-type CD4+ T cell-dependent pathways are not functional. The purpose of this study was to determine whether a similar mechanism might be operative during rejection of rat islet xenografts in mice. First, we observed that eosinophils indeed infiltrate rejected islet grafts together with CD4+ and CD8+ T cells. CD8+ T cell depletion significantly enhanced graft survival and a further prolongation of islet function was obtained in combination with interferon-gamma neutralization. However, islet rejection characterized by prominent eosinophil and macrophage infiltration still occurred in this setting. Although eosinophil infiltrates were dramatically reduced in interleukin-5 deficient mice, the ability of these animals to reject islet xenografts under CD8+ T cell depletion and interferon-gamma neutralization was similar to that of wild-type mice. We conclude that in absence of CD8+ T cells and interferon-gamma, macrophages, but not eosinophils, mediate rejection of rat-to-mouse islet xenografts.

Th2 cytokine profile in infants predisposes to improved graft acceptance after liver transplantation

BACKGROUND

The T helper cell type 1 (Th1) cytokines interleukin (IL)-2 and interferon (IFN)-gamma are mediators of acute graft rejection after liver transplantation and Th2 cytokines, such as IL-4 and IL-10, may have a protective role and correlate with graft acceptance. To test the hypothesis that infants aged <1 year have an immunological advantage with regard to graft acceptance because of a partially immature immune system with a physiological balance toward a Th2 cytokine profile, we conducted the present study.

METHODS

We compared the T helper serum cytokine profiles in 105 infants and children after liver transplantation with or without acute graft rejection and analyzed the normal age-distributed concentrations of T helper cytokines in 51 healthy controls.

RESULTS

The incidence of acute graft rejection was as follows: 0 to 12 months, 26.8%; 1 to 3 years, 40.0%; and >3 years, 71.8%. There was a significantly lower incidence of acute rejection in infants 0 to 12 months of age compared with children >1 year (11/41 vs. 38/64; P=0.001). In healthy infants, significant increasing Th1 cytokine concentrations and decreasing Th2 cytokine concentrations were found with increasing age. Patients with acute rejection had significantly higher values of Th1 cytokines compared with nonrejecting subjects, who had significantly higher concentrations of Th2 cytokines. A longitudinal analysis of serum cytokines from patients showed that changes of the cytokine patterns in the follow-up did not differ significantly from preoperative values, except in the 4 weeks posttransplant.

CONCLUSIONS

We conclude from the data that the physiological balance toward a Th2 cytokine profile of infants in the first months of life predisposes to improved graft acceptance. Transplantation of children with biliary atresia as early as possible, avoiding Th1 stimulation by recurrent infections and vaccinations, may have a positive impact on overall tolerance.

Immunobiology of allograft rejection in the absence of IFN-gamma: CD8+ effector cells develop independently of CD4+ cells and CD40-CD40 ligand interactions

Both wild-type (WT) and IFN-gamma-deficient (IFN-gamma(-/-)) C57BL/6 mice can rapidly reject BALB/c cardiac allografts. When depleted of CD8(+) cells, both WT and IFN-gamma(-/-) mice rejected their allografts, indicating that these mice share a common CD4-mediated, CD8-independent mechanism of rejection. However, when depleted of CD4(+) cells, WT mice accepted their allografts, while IFN-gamma(-/-) recipients rapidly rejected them. Hence, IFN-gamma(-/-), but not WT mice developed an unusual CD8-mediated, CD4-independent, mechanism of allograft rejection. Allograft rejection in IFN-gamma(-/-) mice was associated with intragraft accumulation of IL-4-producing cells, polymorphonuclear leukocytes, and eosinophils. Furthermore, this form of rejection was resistant to treatment with anti-CD40 ligand (CD40L) mAb, which markedly prolonged graft survival in WT mice. T cell depletion studies verified that anti-CD40L treatment failed to prevent CD8-mediated allograft rejection in IFN-gamma(-/-) mice. However, anti-CD40L treatment did prevent CD4-mediated rejection in IFN-gamma(-/-) mice, although grafts were eventually rejected when CD8(+) T cells repopulated the periphery. The IL-4 production and eosinophil influx into the graft that occurred during CD8-mediated rejection were apparently epiphenomenal, since treatment with anti-IL-4 mAb blocked intragraft accumulation of eosinophils, but did not interfere with allograft rejection. These studies demonstrate that a novel, CD8-mediated mechanism of allograft rejection, which is resistant to experimental immunosuppression, can develop when IFN-gamma is limiting. An understanding of this mechanism is confounded by its association with Th2-like immune events, which contribute unique histopathologic features to the graft but are apparently unnecessary for the process of allograft rejection.

Role of STAT4 and STAT6 signaling in allograft rejection and CTLA4-Ig-mediated tolerance

STAT4(-/-) mice have impaired type 1 T cell differentiation, whereas STAT6(-/-) mice fail to generate type 2 responses. The role of type 1 and type 2 T cell differentiation in acute cardiac allograft rejection and in the induction of tolerance was examined in wild-type, STAT4(-/-), and STAT6(-/-) recipients. All recipients rejected the grafts promptly. Analysis of in situ cytokine gene expression in the allografts confirmed decreased levels of IFN-gamma in STAT4(-/-) recipients and undetectable levels of IL-4 and IL-5 in STAT6(-/-) mice. Blockade of the CD28/B7 costimulatory pathway prolonged cardiac graft survival for >100 days in 100% of wild-type and STAT4(-/-) mice. However, 14% of CTLA4-Ig-treated STAT6(-/-) mice rejected their grafts between 20 and 100 days. Moreover, of those animals followed past 100 days, 60% of the STAT6(-/-) mice rejected their grafts. Splenocytes harvested on day 145 posttransplant from CTLA4-Ig-treated rejecting STAT6(-/-) recipients were transfused into syngeneic SCID mice transplanted with donor or third party cardiac allografts. Both donor and third party grafts were rejected, indicating that the initial graft loss may be due to an immunological rejection. In contrast, when splenocytes from CTLA4-Ig-treated wild-type or nonrejecting STAT6(-/-) mice were transferred into SCID recipients, donor allografts were accepted, but third party hearts were rejected. Thus, long-term prolongation of cardiac allograft survival by CTLA4-Ig is STAT4-independent but, at least in part, STAT6-dependent. These data suggest that the balance of type 1 and type 2 T lymphocyte differentiation is not critical for acute rejection but influences the robust tolerance induced by CD28/B7 blockade in this model.

Participation of endogenously produced interferon gamma in interleukin 4-mediated tumor rejection

To elucidate the molecular mechanism underlying IL-4-induced tumor rejection, we challenged mice with a mouse adenocarcinoma cell line, colon 26, genetically engineered to express constitutively IL-4 gene (colon 26/IL-4). Immunocompetent BALB/c mice rejected colon 26/IL-4 cells but not parental cells or cells transduced with a control gene (colon 26/control). Moreover, on rechallenge, parental cells and colon 26/control cells were rejected by normal BALB/c mice that had previously rejected colon 26/IL-4. However, both nude and severe combined immunodeficiency (SCID) mice failed to reject colon 26/IL-4 as well as parental or colon 26/control cells. In contrast, nude mice did reject colon 26/IL-4 after transfer of lymphocytes obtained from the draining lymph nodes of BALB/c mice injected with colon 26/IL-4. These results indicate that challenging mice with colon 26/IL-4 tumor cells resulted in the generation of memory cytotoxic T lymphocytes in the draining lymph nodes. At 3 days after the challenge, IFN-gamma, IL-12 p35, and p40 mRNA expression was selectively enhanced in the draining lymph nodes of mice bearing colon 26/IL-4 cells. Finally, mice deficient in the IFN-gamma gene did not reject colon 26/IL-4 cells. These results suggest that IL-4-induced memory cytotoxic T lymphocyte generation requires IFN-gamma production in the draining lymph nodes, in order to generate a protective immune response.