Asialo GM1 positive CD8+ T cells induce skin allograft rejection in the absence of the secondary lymphoid organs

BACKGROUND: Secondary lymphoid organs are considered to be the only organs in which APCs and na?ve T cells interact to initiate adaptive immune responses. Aly/aly mice are autosomal recessive mutants of C57BL/6 mice, and lack lymph nodes and Peyer's patches. In this study, we investigated immune responses to skin allografts in splenectomized aly/aly mice, which lack secondary lymphoid organs completely, and examined the effect of anti-asialo GM1 (AsGM1) antibodies on these responses. METHODS: Skin allografts were transplanted to 1) heterozygous aly/+ mice, which had normal secondary lymphoid organs, 2) splenectomized aly/+ mice, 3) aly/aly mice, and 4) splenectomized aly/aly mice, with and without anti-AsGM1 antibody treatment. Graft survival time and alloreactive antibody production were investigated. RESULTS: Heterozygous aly/+ mice and splenectomized aly/+ mice rejected skin allografts acutely. Aly/aly mice also rejected skin allografts, but at a later time than aly/+ mice. Sixty percent of splenectomized aly/aly mice rejected skin allografts within 120 days. Serial administration of anti-AsGM1 antibodies prevented skin allograft rejection in splenectomized aly/aly mice during the same 120-day period of observation. After ceasation of anti-AsGM1 antibody treatment, skin allografts were rejected; we observed a simultaneous increase in AsGM1 expression on CD8+ T cells. Alloreactive antibodies were detected in both splenectomized aly/aly mice that rejected skin allografts and in splenectomized aly/aly mice that accepted skin allografts after treatment with anti-AsGM1 antibodies. CONCLUSIONS: Cytotoxic and humoral immune responses to skin allografts could be initiated despite the absence of secondary lymphoid organs. AsGM1+ cells were important effector cells in secondary lymphoid organ-independent skin allograft rejection.     

Interferon Gamma and Contact‐dependent Cytotoxicity Are Each Rate Limiting for Natural Killer Cell–Mediated Antibody‐dependent Chronic Rejection

Natural killer (NK) cells are key components of the innate immune system. In murine cardiac transplant models, donor‐specific antibodies (DSA), in concert with NK cells, are sufficient to inflict chronic allograft vasculopathy independently of T and B cells. In this study, we aimed to determine the effector mechanism(s) required by NK cells to trigger chronic allograft vasculopathy during antibody‐mediated rejection. Specifically, we tested the relative contribution of the proinflammatory cytokine interferon gamma (IFN‐γ) versus the contact‐dependent cytotoxic mediators of perforin and the CD95/CD95L (Fas/Fas ligand [FasL]) pathway for triggering these lesions. C3H/HeJ cardiac allografts were transplanted into immune‐deficient C57BL/6 rag^?/?γc^?/? recipients, who also received monoclonal anti–major histocompatibility complex (MHC) class I DSA. The combination of DSA and wild‐type NK cell transfer triggered aggressive chronic allograft vasculopathy. However, transfer of IFN‐γ–deficient NK cells or host IFN‐γ neutralization led to amelioration of these lesions. Use of either perforin‐deficient NK cells or CD95 (Fas)–deficient donors alone did not alter development of vasculopathy, but simultaneous disruption of NK cell–derived perforin and allograft Fas expression resulted in prevention of these abnormalities. Therefore, both NK cell IFN‐γ production and contact‐dependent cytotoxic activity are rate‐limiting effector pathways that contribute to this form of antibody‐induced chronic allograft vasculopathy.     

B cells assist allograft rejection in the deficiency of protein kinase c‐theta

We have previously shown that mice deficient in protein kinase C theta (PKCθ) have the ability to reject cardiac allografts, but are susceptible to tolerance induction. Here we tested role of B cells in assisting alloimmune responses in the absence of PKCθ. Mouse cardiac allograft transplantations were performed from Balb/c (H‐2d) to PKCθ knockout (PKCθ^?/?), PKCθ and B cell double‐knockout (PBDK, H‐2b) mice and wild‐type (WT) C57BL/6 (H‐2b) mice. PBDK mice spontaneously accepted the allografts with the inhibition of NF‐κB activation in the donor cardiac allograft. Anti‐B cell antibody (rituximab) significantly delayed allograft rejection in PKCθ^?/?, but not in WT mice. Co‐transfer of PKCθ^?/? T plus PKCθ^?/? B cells or primed sera triggered allograft rejection in Rag1^?/? mice, and only major histocompatibility complex class II‐enriched B cells, but not class I‐enriched B cells, were able to promote rejection. This, together with the inability of PKCθ^?/? and CD28^?/? double‐deficient (PCDK) mice to acutely reject allografts, suggested that an effective cognate interaction between PKCθ^?/? T and B cells for acute rejection is CD28 molecule dependent. We conclude that T–B cell interactions synergize with PKCθ^?/? T cells to mediate acute allograft rejection.     

Differential Requirement of CD27 Costimulatory Signaling for Naïve Versus Alloantigen‐Primed Effector/Memory CD8+ T Cells

CD8⁺ memory T cells endanger allograft survival by causing acute and chronic rejection and prevent tolerance induction. We explored the role of CD27:CD70 T‐cell costimulatory pathway in alloreactive CD8⁺/CD4⁺ T‐cell activation. CD27‐deficient (CD27^?/?) and wild‐type (WT) B6 mice rejected BALB/c cardiac allografts at similar tempo, with or without depletion of CD4⁺ or CD8⁺ T cells, suggesting that CD27 is not essential during primary T‐cell alloimmune responses. To dissect the role of CD27 in primed effector and memory alloreactive T cells, CD27^?/? or WT mice were challenged with BALB/c hearts either 10 or 40 days after sensitization with donor‐type skin grafts. Compared to WT controls, allograft survival was prolonged in day 40‐ but not day 10‐sensitized CD27^?/? recipients. Improved allograft survival was accompanied by diminished secondary responsiveness of memory CD8⁺ T cells, which resulted from deficiency in memory formation rather than their lack of secondary expansion. Chronic allograft vasculopathy and fibrosis were diminished in CD27^?/? recipients of class I‐ but not class II‐mismatched hearts as compared to WT controls. These data establish a novel role for CD27 as an important costimulatory molecule for alloreactive CD8⁺ memory T cells in acute and chronic allograft rejection.     

Antibody‐Mediated Rejection of Single Class I MHC‐Disparate Cardiac Allografts

Murine CCR5^?/? recipients produce high titers of antibody to complete MHC‐mismatched heart and renal allografts. To study mechanisms of class I MHC antibody‐mediated allograft injury, we tested the rejection of heart allografts transgenically expressing a single class I MHC disparity in wild‐type C57BL/6 (H‐2^b) and B6.CCR5^?/? recipients. Donor‐specific antibody titers in CCR5^?/? recipients were 30‐fold higher than in wild‐type recipients. B6.K^d allografts survived longer than 60 days in wild‐type recipients whereas CCR5^?/? recipients rejected all allografts within 14 days. Rejection was accompanied by infiltration of CD8 T cells, neutrophils and macrophages, and C4d deposition in the graft capillaries. B6.K^d allografts were rejected by CD8^?/?/CCR5^?/?, but not μMT^?/?/CCR5^?/?, recipients indicating the need for antibody but not CD8 T cells. Grafts recovered at day 10 from CCR5^?/? and CD8^?/?/CCR5^?/? recipients and from RAG‐1^?/? allograft recipients injected with anti‐K^d antibodies expressed high levels of perforin, myeloperoxidase and CCL5 mRNA. These studies indicate that the continual production of antidonor class I MHC antibody can mediate allograft rejection, that donor‐reactive CD8 T cells synergize with the antibody to contribute to rejection, and that expression of three biomarkers during rejection can occur in the absence of this CD8 T cell activity.     

IL‐17 Deficiency Attenuates Allograft Injury and Prolongs Survival in a Murine Model of Fully MHC‐Mismatched Renal Allograft Transplantation

IL‐17 is a pro‐inflammatory cytokine implicated in the pathogenesis of inflammatory and autoimmune diseases. However the role of IL‐17 in renal allograft rejection has not been fully explored. Here, we investigate the impact of IL‐17 in a fully MHC‐mismatched, life‐sustaining, murine model of kidney allograft rejection using IL‐17 deficient donors and recipients (IL‐17^?/? allografts). IL‐17^?/? allografts exhibited prolonged survival which was associated with reduced expression of the Th1 cytokine IFN‐γ and histological attenuation of acute and chronic allograft rejection, as compared to wild‐type allograft recipients. Results were confirmed in WT allograft recipients treated with an IL‐17 blocking antibody. Subsequent experiments using either donors or recipients deficient in IL‐17 showed a trend towards prolongation of survival only when recipients were IL‐17^?/?. Administration of a depleting anti‐CD25 antibody to IL‐17^?/? recipients abrogated the survival advantage conferred by IL‐17 deficiency, suggesting the involvement of a CD4⁺CD25⁺ T cell regulatory mechanism. Therefore, IL‐17 deficiency or neutralization was protective against the development of kidney allograft rejection, which may be mediated by impairment of Th1 responses and/or enhanced protection by Tregs.

     

A novel pathway of chronic allograft rejection mediated by NK cells and alloantibody

Chronic allograft vasculopathy (CAV) in murine heart allografts can be elicited by adoptive transfer of donor specific antibody (DSA) to class I MHC antigens and is independent of complement. Here we address the mechanism by which DSA causes CAV. B6.RAG1^?/? or B6.RAG1^?/?C3^?/? (H‐2^b) mice received B10.BR (H‐2^k) heart allografts and repeated doses of IgG2a, IgG1 or F(ab’)₂ fragments of IgG2a DSA (anti‐H‐2^k). Intact DSA regularly elicited markedly stenotic CAV in recipients over 28 days. In contrast, depletion of NK cells with anti‐NK1.1 reduced significantly DSA‐induced CAV, as judged morphometrically. Recipients genetically deficient in mature NK cells (γ‐chain knock out) also showed decreased severity of DSA‐induced CAV. Direct NK reactivity to the graft was not necessary. F(ab’)₂ DSA fragments, even at doses twofold higher than intact DSA, were inactive. Graft microvascular endothelial cells responded to DSA in vivo by increased expression of phospho‐extracellular signal‐regulated kinase (pERK), a response not elicited by F(ab’)₂ DSA. We conclude that antibody mediates CAV through NK cells, by an Fc dependent manner. This new pathway adds to the possible mechanisms of chronic rejection and may relate to the recently described C4d‐negative chronic antibody‐mediated rejection in humans.     

Innate immunity and cardiac allograft rejection

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of heart transplantation as a therapy for end-stage heart failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained clinical significance as mounting evidence now indicates that innate immune responses have important roles in the acute and chronic rejection of cardiac allografts including cardiac allograft vasculopathy (CAV). Whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and in the development of CAV. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection. Finally, new data indicate that activation of complement is linked to acute rejection and CAV. In summary, the conventional wisdom that the innate immune system is of little importance in whole-organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, and complement will be necessary to prevent CAV completely and to eventually achieve long-term tolerance to cardiac allografts.     

In Vivo Function of Immune Inhibitory Molecule B7‐H4 in Alloimmune Responses

B7 ligands deliver both costimulatory and coinhibitory signals to the CD28 family of receptors on T lymphocytes, the balance between which determines the ultimate immune response. Although B7‐H4, a recently discovered member of the B7 family, is known to negatively regulate T cell immunity in autoimmunity and cancer, its role in solid organ allograft rejection and tolerance has not been established. Targeting the B7‐H4 molecule by a blocking antibody or use of B7‐H4^?/? mice as recipients of fully MHC‐mismatched cardiac allografts did not affect graft survival. However, B7‐H4 blockade resulted in accelerated allograft rejection in CD28‐deficient recipients. B7‐1/B7‐2‐double‐deficient recipients are truly independent of CD28/CTLA‐4:B7 signals and usually accept MHC‐mismatched heart allografts. Blockade of B7‐H4 in these mice also precipitated rejection, demonstrating regulatory function of this molecule independent of an intact CD28/CTLA‐4:B7 costimulatory pathway. Accelerated allograft rejection was always accompanied by increased frequencies of alloreactive IFN‐γ‐, IL‐4‐ and Granzyme B‐producing splenocytes. Finally, intact recipient, but not donor, B7‐H4 is essential for prolongation of allograft survival by blocking CD28/CTLA4:B7 pathway using CTLA4‐Ig. These data are the first to provide evidence of the regulatory effects of B7‐H4 in alloimmune responses in a murine model of solid organ transplantation.     

The Effect of a Novel Immunosuppressant, FTY720, in Mice Without Secondary Lymphoid Organs

Purpose FTY720 is a novel immunosuppressive agent that is thought to reduce the number of peripheral blood lymphocytes (PBL) by directing them toward secondary lymphoid organs such as the lymph nodes and Peyer’s patches. We studied the effects of FTY720 on aly/aly mice that do not have either lymph nodes or Peyer’s patches, as well as on splenectomized aly/aly mice.Methods FTY720 was orally administered by gavage (1 mg/kg) to aly/aly mice as well as to aly/+ mice with and without a splenectomy on 14 consecutive days. The number of lymphocytes was then counted using True Cell beads and flow cytometry. The number of B220-, CD3-, and CD4-positive cells was also determined. In addition, skin grafts from C3H donor mice were performed on these mice.Results FTY720 was effective in significantly reducing the total lymphocyte count as well as the B220-, CD3-, and CD4-positive subtypes in the peripheral blood of aly/+ mice as well as in aly/aly mice with and without a splenectomy. While we did observe allograft skin graft rejection in both the aly/+ mice as well as the aly/aly mice recipients and splenectomized aly/aly mice, the graft survival was prolonged in all groups. The skin allografts treated by FTY720 thus demonstrated fewer lymphocytic cells and less infiltration of CD4-positive cells.Conclusions The administration of FTY720 to mice without lymph nodes, Peyer’s patches, or spleens still results in peripheral lymphopenia. In all groups, FTY720 was found to prevent the infiltration of CD4-positive cells in skin allografts while also prolonging skin allograft survival. The fate of these lymphocytes, however, is unclear.     

Transplant long-surviving induced by CD40-CD40 ligand costimulation blockade is dependent on IFN-γ through its effect on CD4(+)CD25(+) regulatory T cells

BackgroundIFN-γ was documented to be commonly associated with acute rejection. In the present study, we investigated the role of IFN-γ in the transplant long-surviving induced by blocking CD40–CD40 ligand (CD40–CD40L) costimulation and its mechanisms.MethodsIFN-γ expression in cardiac allografts and spleens from syngeneic and allogeneic recipients with or without anti-CD40L monoclonal antibody (MR-1) treatment was examined by real-time RT-PCR. The grafts survival time in Wild type (IFN-γ^+/+) and IFN-γ deficient (IFN-γ^?/?) recipients was investigated. Mixed lymphocyte reaction (MLR) of CD4⁺ T cells and cytotoxic T lymphocyte (CTL) assay of CD8⁺ T cells were also studied. FoxP3 expression in allografts and spleens from IFN-γ^+/+ or IFN-γ^?/? recipients with MR-1 treatment was examined. Furthermore, FoxP3, IL-10 and CTLA-4 expressions and the suppressive capability of CD4⁺CD25⁺ regulatory T cells were examined.ResultsRejected allografts showed significantly higher IFN-γ expression than long-surviving allografts. Allograft survival was not prolonged in nonimmunosuppressed IFN-γ^?/? mice. Administration of MR-1 induced long-term survival in 90.1% of IFN-γ^+/+ recipients (98 ± 6.6 days) but failed to do so in IFN-γ^?/? group (16.2 ± 4.0 days). IFN-γ^?/? recipients facilitated the proliferation and CTL generation of T cells. The allografts and spleens from IFN-γ^+/+ recipients contained higher FoxP3 expression than IFN-γ^?/? recipients. Moreover, CD4⁺CD25⁺ T cells from IFN-γ^+/+ recipients displayed a higher FoxP3 and IL-10 expression and suppressive capability.ConclusionIFN-γ plays an important role in the long-surviving induced by blocking CD40–CD40L through inhibiting the function of activated T cells and increasing suppressive capability of CD4⁺CD25⁺ regulatory T cells.     

Expression Pattern of Tumor Necrosis Factor-α–Induced Protein 8-Like 2 in Acute Rejection of Cardiac Allograft

Background

Tumor necrosis factor-α–induced protein-8 like-2 (TIPE2) is a negative regulator of innate immunity and cellular immunity, yet the expression pattern of TIPE2 in acute rejection of cardiac allograft remain enigmatic.

Deletion of the activating NK cell receptor NKG2D accelerates rejection of cardiac allografts

It has already been shown that neutralization of the activating NK cell receptor NKG2D in combination with co‐stimulation blockade prolongs graft survival of vascularized transplants. In order to clarify the underlying cellular mechanisms, we transplanted complete MHC‐disparate BALB/c‐derived cardiac grafts into C57BL/6 wildtypes or mice deficient for NKG2D (Klrk1^?/?). Although median survival was 8 days for both recipient groups, we detected already at day 5 posttransplantation significantly greater intragraft frequencies of NKp46⁺ NK cells in Klrk1^?/? recipients than in wildtypes. This was followed by a significantly greater infiltration of CD4⁺, but a lesser infiltration of CD8⁺ T cell frequencies. Contrary to published observations, co‐stimulation blockade with CTLA4‐Ig resulted in a significant acceleration of cardiac rejection by Klrk1^?/? recipients, and this result was confirmed by applying a neutralizing antibody against NKG2D to wildtypes. In both experimental setups, grafts derived from Klrk1^?/? recipients were characterized by significantly higher levels of interferon‐γ mRNA, and both CD4⁺ and CD8⁺ T cells displayed a greater capacity for degranulation and interferon‐γ production. In summary, our results clearly illustrate that NKG2D expression in the recipient is important for cardiac allograft survival, thus supporting the hypothesis that impairment of NK cells prevents the establishment of graft acceptance.     

Allergic Conjunctivitis Renders CD4+ T Cells Resistant to T Regulatory Cells and Exacerbates Corneal Allograft Rejection

Allergic diseases rob corneal allografts of immune privilege and increase immune rejection. Corneal allograft rejection in BALB/c allergic hosts was analyzed using a short ragweed (SWR) pollen model of allergic conjunctivitis. Allergic conjunctivitis did not induce exaggerated T‐cell responses to donor C57BL/6 (B6) alloantigens or stimulate cytotoxic T lymphocyte (CTL) responses. Allergic conjunctivitis did affect T regulatory cells (Tregs) that support graft survival. Exogenous IL‐4, but not IL‐5 or IL‐13, prevented Treg suppression of CD4⁺ effector T cells isolated from naïve mice. However, mice with allergic conjunctivitis developed Tregs that suppressed CD4⁺ effector T‐cell proliferation. In addition, IL‐4 did not inhibit Treg suppression of IL‐4Rα^?/? CD4⁺ T‐cell responses, suggesting that IL‐4 rendered effector T cells resistant to Tregs. SRW‐sensitized IL‐4Rα^?/? mice displayed the same 50% graft survival as nonallergic WT mice, that was significantly less than the 100% rejection that occurred in allergic WT hosts, supporting the role of IL‐4 in the abrogation of immune privilege. Moreover, exacerbation of corneal allograft rejection in allergic mice was reversed by administering anti‐IL‐4 antibody. Thus, allergy‐induced exacerbation of corneal graft rejection is due to the production of IL‐4, which renders effector T cells resistant to Treg suppression of alloimmune responses.     

The Role of Lymphocyte Subset in Predicting Allograft Rejections in Kidney Transplant Recipients

BackgroundAllograft rejection remains a significant challenge in managing post-transplant recipients despite the improvement in immunologic risk assessment and immunosuppressive therapy. Published literature including animal studies has demonstrated that the cells responsible for rejection are beyond the innate T and B cells, and other studies revealed evidence supporting natural killer (NK) cells’ role in kidney allograft injury. This study aims to find the association between the peripheral blood lymphocyte subset counts, primarily NK cells, and the kidney allograft biopsy findings.MethodsThis is a prospective cross-sectional study among a total of 100 kidney allograft biopsies in 61 kidney transplant recipients. The peripheral blood for the lymphocyte subset was sent just before the allograft biopsy. The patients' immunosuppression and other laboratory investigations were managed as per clinical practices by the attending nephrologist.ResultsOverall, the mean age of our patients was 43.72 ± 10.68 years old, and 55.7% of recipients were male. Higher counts of T cells (CD4+; 658.8 ± 441.4 cells/µL; P = .043) and NK cells (CD3-CD16+CD56+; 188 [interquartile range = 133.0-363.0 cells/µL]; P = .002) were associated with higher risk of allograft rejection in the initial analysis. Patients with an allograft age <12 months had significantly higher total T cells, CD4+ T cells, and NK cells in the rejection groups. However, after assessing factors associated with rejection in the multivariate analysis, we only found that being ABO-incompatible and having >497 CD4+ cells/µL had a higher odds of allograft rejection.ConclusionsHigher CD4± counts were associated with a higher risk of allograft rejection. However, there was no significant increase in CD8±, CD19±, and NK cells count in our cohort with allograft rejection.     

Loss of DRAK2 Signaling Enhances Allogeneic Transplant Survival by Limiting Effector and Memory T Cell Responses

Here, we demonstrate that loss of DRAK2 signaling significantly promotes the acceptance of allogeneic engraftment in two separate transplant models without promoting generalized immunosuppression. Drak2?/? T cells failed to reject allogeneic tumors, and were defective in rejecting Balb/C allogeneic skin grafts on C57BL6/J recipients. A significant fraction of alloreactive Drak2?/? T cells underwent apoptosis following activation, whereas enforced expression of Bcl‐xL in Drak2?/? T cells restored allograft rejection. Formation of allogeneic memory was also greatly hampered in T cells lacking the Drak2 gene. Adoptive transfer of memory T cells from Drak2?/? mice failed to promote the rejection of allogeneic tumors, and such cells led to significantly delayed rejection of skin allografts in the Balb/C‐>C57BL/6J model. Costimulatory blockade by in vivo administration of Cytotoxic T‐Lymphocyte Antigen 4 fusion protein (CTLA4‐Ig) synergized with the DRAK2 deficiency and led to long‐term allogeneic skin graft acceptance. Overall, these results demonstrate that DRAK2 plays an important role in primary and memory T cell responsiveness to allografts. Because previous studies have demonstrated that a loss of DRAK2 does not negatively impact antiviral immunity, the studies here underscore the potential utility of pharmacological blockade of DRAK2 to achieve transplant maintenance without the imposition of generalized immunosuppression.     

The natural killer cell activating receptor,NKG2D,is critical to antibody-dependent chronic rejection in heart transplantation

Chronic rejection is among the most pressing clinical challenges in solid organ transplantation. Interestingly, in a mouse model of heterotopic heart transplantation, antibody-dependent, natural killer (NK) cell-mediated chronic cardiac allograft vasculopathy occurs in some donor–recipient strain combinations, but not others. In this study, we sought to identify the mechanism underlying this unexplained phenomenon. Cardiac allografts from major histocompatibility complex (MHC) mismatched donors were transplanted into immune-deficient C57Bl/6.rag^−/− recipients, followed by administration of a monoclonal antibody against the donor MHC class I antigen. We found marked allograft vasculopathy in hearts from C3H donors, but near-complete protection of BALB/c allografts from injury. We found no difference in recipient NK cell phenotype or intrinsic responsiveness to activating signals between recipients of C3H versus BALB/c allografts. However, cardiac endothelial cells from C3H allografts showed an approximately twofold higher expression of Rae-1, an activating ligand of the NK cell receptor natural killer group 2D (NKG2D). Importantly, the administration of a neutralizing antibody against NKG2D abrogated the development of allograft vasculopathy in recipients of C3H allografts, even in the presence of donor-specific antibodies. Therefore, the activating NK cell receptor NKG2D is necessary in this model of chronic cardiac allograft vasculopathy, and strain-dependent expression of NK activating ligands correlates with the development of this disease.     

Immunopathogenesis of accelerated allograft rejection in sensitized recipients: humoral and nonhumoral mechanisms

INTRODUCTION: Accelerated rejection (AccR) in sensitized recipients (second-set rejection) is considered a classic humorally mediated form of allograft rejection, although additional effector mechanisms may be involved. METHODS: We developed a model of AccR in which C57BL6 mice are sensitized by BALB/c skin grafts, followed 10 days later by transplantation of BALB/c hearts. We undertook analysis of various humoral and cellular components in this model using knockout or monoclonal antibody-treated allograft recipients. RESULTS: Sensitized mice rejected cardiac allografts in 34+/-7 hr. AccR was accompanied by endothelial deposition of immunoglobulins, complement, and fibrin, but also by dense expression of multiple chemokines and a mixed polymorphonuclear and mononuclear cellular infiltrate. Whereas neutrophil or complement depletion had no significant effect on the tempo of AccR, surprisingly B cell-deficient recipients still underwent AccR (41+/-7 hr) in conjunction with T cell and macrophage recruitment. In contrast, T cell-deficient (nude) mice maintained functioning cardiac allografts for >720 hr despite prior skin engraftment. CONCLUSIONS: AccR in sensitized experimental recipients involves multiple effector pathways. Although most previous studies have emphasized the key role of humoral pathways in mediating AccR, our data indicate that T cell-dependent mechanisms can also promote AccR, alone or in conjunction with humoral responses.     

Role of Natural Killer Cells in the Innate Immune System After Intraportal Islet Transplantation in Mice

Background

Both liver natural killer (NK) and NK T cells of the innate immune system play a crucial role in islet graft loss after intraportal islet transplantation, although a relationship between NK and NK T cells in islet loss has not been proven. In this study, we investigated the role of NK cells in the innate immune system in islet graft loss after intraportal islet transplantation.