LIVER TRANSPLANTATION-INDUCED ANTIHISTONE H1 AUTOANTIBODIES SUPPRESS MIXED LYMPHOCYTE REACTION

Identification of High-Mobility Group Box 1 (HMGB1) Expression as a Potential Predictor of Rejection and Poor Prognosis After Liver Transplantation

BACKGROUND Acute cellular rejection (ACR) frequently occurs after liver transplantation (LT) and can result in permanent damage of the liver allograft. Specific and sensitive biomarkers for predicting and monitoring ACR are vital for guiding post-transplantation care. In the present study, we aimed to investigate the function of high-mobility group box 1 (HMGB1) in predicting ACR and prognosis after LT. MATERIAL AND METHODS A total of 113 LT recipients were enrolled in the study, including 62 patients in an ACR group and 51 patients in a non-rejection group. Using tissues from the 113 patients, HMGB1 expression was examined by immunohistochemistry, and the total score for HMGB1 expression was calculated by multiplying the percentage of immunoreactive cells score and the staining intensity score. We then analyzed the association between HMGB1 expression and clinical features. Finally, the function of HMGB1 in predicting the prognosis of LT was determined using Kaplan-Meier (K-M) survival and Cox multivariate analyses. RESULTS Immunohistochemical staining results demonstrated that the expression of HMGB1 was significantly increased in the ACR group, compared with that in the non-rejection group (P<0.05). Clinical characteristic analysis revealed that high HMGB1 levels were related to ACR (P<0.05). Moreover, K-M survival analysis showed that patients with high HMGB1 expression displayed poorer prognosis (P<0.05). Cox multivariate analysis demonstrated that HMGB1 was an independent prognostic predictor for post-LT survival (odds ratio, 3.283; P=0.008). CONCLUSIONS LT recipients' HMGB1 levels may be a useful and noninvasive biomarker for the prediction of ACR and prognosis after LT.

Impact of Histone H1 on the Progression of Allergic Rhinitis and Its Suppression by Neutralizing Antibody in Mice

Nuclear antigens are known to trigger off innate and adaptive immune responses. Recent studies have found that the complex of nucleic acids and core histones that are derived from damaged cells may regulate allergic responses. However, no fundamental study has been performed concerning the role of linker histone H1 in mast cell-mediated type I hyperreactivity. In this study, we explored the impact of histone H1 on mast cell-mediated allergic responses both in vitro and in vivo. In the course of a bona-fide experimental allergen sensitization model upon co-injection with alum adjuvant, ovalbumin (OVA), but not PBS, induced elevated levels of circulating histone H1. Intranasal challenge with histone H1 to OVA/alum- (but not PBS/alum)-sensitized mice induced significantly severer symptoms of allergic rhinitis than those in mice sensitized and challenged with OVA. A monoclonal antibody against histone H1 not only suppressed mast cell degranulation, but also ameliorated OVA-induced nasal hyperreactivity and IgE-mediated passive cutaneous anaphylaxis. Our present data suggest that nuclear histone H1 represents an alarmin-like endogenous mediator acting on mast cells, and that its blockage has a therapeutic potential for mast cell-mediated type I hyperreactivity.

Induction of antinuclear antibodies by de novo autoimmune hepatitis regulates alloimmune responses in rat liver transplantation

Concanavalin A (Con A) is a lectin originating from the jack-bean and well known for its ability to stimulate T cells and induce autoimmune hepatitis. We previously demonstrated the induction of immunosuppressive antinuclear autoantibody in the course of Con A-induced transient autoimmune hepatitis. This study aimed to clarify the effects of Con A-induced hepatitis on liver allograft rejection and acceptance. In this study, we observed the unique phenomenon that the induction of transient de novo autoimmune hepatitis by Con A injection paradoxically overcomes the rejection without any immunosuppressive drug and exhibits significantly prolonged survival after orthotopic liver transplantation (OLT). Significantly increased titers of anti-nuclear Abs against histone H1 and high-mobility group box 1 (HMGB1) and reduced donor specific alloantibody response were observed in Con A-injected recipients. Induction of Foxp3 and IL-10 in OLT livers of Con A-injected recipients suggested the involvement of regulatory T cells in this unique phenomenon. Our present data suggest the significance of autoimmune responses against nuclear histone H1 and HMGB1 for competing allogeneic immune responses, resulting in the acceptance of liver allografts in experimental liver transplantation.

Nuclear antigens and auto/alloantibody responses: friend or foe in transplant immunology

In addition to cellular immune responses, humoral immune responses, mediated by natural antibodies, autoantibodies, and alloantibodies, have increasingly been recognized as causes of organ transplant rejection. In our previous studies, we have demonstrated the induction of antinuclear antibodies against histone H1 and high-mobility group box 1 (HMGB1), in both experimental and clinical liver transplant tolerance. The active induction of antinuclear antibodies is usually an undesirable phenomenon, but it is often observed after liver transplantation. However, the release of nuclear antigens and its suppression by neutralizing antibodies are proposed to be important in the initiation and regulation of immune responses. In this review article, we summarize the current understanding of nuclear antigens and corresponding antinuclear regulatory antibodies (Abregs) on infection, injury, inflammation, transplant rejection, and tolerance induction and discuss the significance of nuclear antigens as diagnostic and therapeutic targets.

Unexpected T cell regulatory activity of anti-histone H1 autoantibody: its mode of action in regulatory T cell-dependent and -independent manners

Induction of anti-nuclear antibodies against DNA or histones is a hallmark of autoimmune disorders, but their actual contribution to disease predisposition remains to be clarified. We have previously reported that autoantibodies against histone H1 work as a critical graft survival factor in a rat model of tolerogeneic liver transplantation. Here we show that an immunosuppressive anti-histone H1 monoclonal antibody (anti-H1 mAb) acts directly on T cells to inhibit their activation in response to T cell receptor (TCR) ligation. Intriguingly, the T cell activation inhibitory activity of anti-H1 mAb under suboptimal dosages required regulatory T (Treg) cells, while high dose stimulation with anti-H1 mAb triggered a Treg cell-independent, direct negative regulation of T cell activation upon TCR cross-linking. In the Treg cell-dependent mode of immunosuppressive action, anti-H1 mAb did not induce the expansion of CD4(+-)Foxp3(+) Treg cells, but rather potentiated their regulatory capacity. These results reveal a previously unappreciated T cell regulatory role of anti-H1 autoantibody, whose overproduction is generally thought to be pathogenic in the autoimmune settings.

Immunological and regenerative aspects of hepatic mast cells in liver allograft rejection and tolerance

The precise roles of mast cells in liver allograft rejection and tolerance are still unknown. This study aimed to explore the roles of mast cells in immune regulation and liver regeneration for tolerance induction by using rat models of orthotopic liver transplantation (OLT). Stem cell factor (SCF) and its receptor c-Kit, which are critical to the migration and development of not only stem cells but also mast cells, significantly increased in the tolerogenic livers as compared with rejected livers. The significant elevation of mast cell tryptase, high-affinity IgE receptor, and histamine suggested the activation of mast cells in liver allografts at the tolerogenic phase after OLT. Immunohistochemical analysis using confocal microscope clearly showed colocalization of mast cells, Foxp3+ Tregs, γδ T cells, and recipient-derived hepatic progenitor cells with higher expression of SCF, IL-9, IL-10, TGF-β1, and IL-17 related to immunoregulation and liver regeneration in the donor grafts of a tolerogenic OLT model. Cross-talk among mast cells and other cells was evaluated by in vitro studies demonstrating that syngeneic bone marrow-derived mast cells (BMMCs) co-cultured with naïve splenocytes or primary hepatocytes significantly increased the population of splenic γδ T cells by mitogen stimulation or by mast cell degranulation, and also significantly induced the hepatocyte proliferation, respectively. Our results suggested that mast cells in the donor grafts may play important roles in the induction/maintenance of immune tolerance and liver regeneration resulting in the replacement of hepatic cells from donor to recipient.

Monoclonal antibody produced against calf thymus histone

The localization and modification of histone play a prime role in the regulation of unelucidated biochemical pathways, such as apoptosis and cell proliferatory-inhibitory activities. Thus studying histone reveals cell proliferation and its biochemical processes. Therefore anti-histone antibody production is important in order to isolate, purify, identify, and separate histone from cultured cells. In order to produce anti-histone antibodies by hybridoma, 8-week-old female BALB/c mice were immunized with commercially procured whole calf thymus histone. Subsequently the spleen cells of the immunized BALB/c and SP2/O-AG-14 myeloma cells were fused using polyethylene glycol, which resulted in 16 clones. Out of these 16 clones, only one, 1D7, was found to be specific to our antigen (calf thymus histone) by ELISA. The supernatant of the positive clone 1D7 was used in immunoblotting to characterize the specificity of the produced monoclonal antibody. Immunoblotting confirmed that the monoclonal antibody produced from 1D7 clone is specific to histone H1 epitope present in the calf thymus. Our results suggest that to generate more potent monoclonal antibody reagent specific for many different epitopes present on histone, a larger number of fusions are required. Further, if such potent monoclonal antibody reagent is produced, it will be an indispensable tool in elucidating the role of H1 in apoptosis and cell proliferatory-inhibitory activities. This reagent can be used for diagnosis of antihistone antibody in SLE patient's serum, for testing the viability of cultured monocytes, and for localization of histone in metaphase chromosomes.

Immunological aspects and therapeutic significance of an autoantibody against histone H1 in a rat model of concanavalin A-induced hepatitis

We previously demonstrated the immunosuppressive activity of anti-histone H1 autoantibody induced in experimental and clinical liver allograft tolerance. This study aimed to explore the immunological aspects of anti-histone H1 autoantibody in liver injury induced by concanavalin A (Con A). To establish a Con A-hepatitis model, 20 mg/kg Con A was intravenously injected into rats, after which liver function and histopathological analyses were performed. In this model, anti-histone H1 autoantibody was transiently induced in the sera during the natural recovery stage, 3-7 days after Con A injection. To evaluate the therapeutic significance of anti-histone H1 autoantibody, a polyclonal antibody against histone H1 was intraperitoneally injected immediately after Con A injection. We found that injection of anti-histone H1 antibody could reduce Con A-induced liver damage. Further mechanical analyses revealed that anti-histone H1 antibody altered the intracellular activation of mitogen-activated protein kinase, nuclear factor-kappaB and calcineurin via T-cell receptor signalling, suggesting that anti-histone H1 antibody may protect the liver from Con A-induced injury by inhibiting activation of effector T cells. These findings suggest that anti-histone H1 autoantibody may be a natural immune regulatory factor that protects inflamed livers suffering from autoimmune hepatitis and may lead to T-cell unresponsiveness through the selective regulation of mitogen-activated protein kinase/nuclear factor-kappaB and calcineurin signalling.

A novel peptide mimotope identified as a potential immunosuppressive vaccine for organ transplantation

We reported that anti-histone H1 autoantibody is one of the main immunosuppressive factors in serum that is induced after orthotopic liver transplantation in a rat tolerogenic model. We generated a novel anti-histone H1 IgM mAb produced by hybridoma 16G9 (16G9 mAb) that shows MLR-inhibitory activity. Identification of a functional epitope responsible for the immunosuppressive activity of 16G9 mAb may lead to the establishment of a novel therapeutic strategy. We used a combinatorial phage display peptide library to screen for peptides that bind to 16G9 mAb. Consequently, two peptides that bind to 16G9 mAb, SSV and LPQ, were selected from the library. The binding of 16G9 mAb to histone H1 was inhibited by SSV. SSV was recognized by rat tolerogenic post-orthotopic liver transplantation serum and the binding to SSV was inhibited by histone H1. Mice were immunized with keyhole limpet hemocyanin-conjugated SSV and LPQ. Abs induced by SSV immunization inhibited Con A-stimulated splenocyte proliferation, and the inhibition was neutralized by preincubation with SSV. Splenocytes stimulated by anti-CD3 Ab were inhibited by SSV-induced Abs using CFSE labeling. SSV immunization in rats before heterotopic heart transplantation resulted in significant prolonged allograft survival. These findings suggested that SSV is a functional histone H1-binding epitope for 16G9 mAb. SSV is capable of determining serum immunoreactivity against histone H1 as an index marker for tolerance. The inhibitory activity of SSV-induced Abs on blast cell proliferation and the prolonged graft survival that results from SSV immunization imply a potential for the development of an immunosuppressive vaccine.

Immunological role of indoleamine 2,3-dioxygenase in rat liver allograft rejection and tolerance

BACKGROUND AND AIM

Indoleamine 2,3-dioxygenase (IDO) is expressed in the placenta and plays an essential role in maternal tolerance. Recent data showed that giving IDO inhibitor blocked liver allograft tolerance. However, the immunological role of IDO in rat liver allograft models has not been characterized. In the present study, the time-course of IDO expression and the localization of IDO were analyzed to address the role of IDO in the induction of tolerance.

METHODS

Rat orthotopic liver transplantations (OLT) were performed and IDO gene expression of OLT livers was analyzed. Immunohistochemistry was used to evaluate the localization of IDO-expressed cells in the liver.

RESULTS

The IDO gene was detected in the allogeneic liver graft at the acute phase but the signal could not be detected when these OLT rats were treated with cyclosporinee A. The time-course of IDO gene expression in liver grafts of the spontaneous tolerant OLT model revealed that the IDO mRNA was expressed in both the rejection phase and the induction phase of tolerance, but the signal was gradually lowered during the maintenance phase of tolerance. Immunohistochemistry confirmed that the IDO protein was detected in antigen-presenting cells but not in hepatocytes.

CONCLUSION

Our results demonstrated that IDO is induced in antigen-presenting cells of rat liver allografts under drug-free status, suggesting that indirect or direct recognition of donor antigen and further T-cell activation may be inhibited. IDO may act as a local immunosuppressive molecule to protect transplanted cells, tissues and organs from immune attack.

Involvement of autoimmunity against nuclear histone H1 in liver transplantation tolerance

BACKGROUND

Our recent studies suggested that anti-histone H1 autoantibody (auto-Ab) plays an important role in experimental and clinical liver allograft tolerance as a natural immunosuppressive factor. The present study aimed to explore how the autoimmune response against histone H1 is involved in tolerance induction.

METHODS

The measurement of anti-histone H1 auto-Ab and immunohistochemical analysis were performed in serum and liver allografts after orthotopic liver transplantation (OLT). To compare the auto-Ab response against histone H1 between the recipients of rejector (DA-LEW) and tolerogenic (DA-PVG) OLT models, naïve recipients were immunized with calf thymus histone H1. The immunosuppressive state of histone H1-immunized rats was assayed by mixed lymphocyte reaction (MLR).

RESULTS

Anti-histone H1 Ab titer was transiently increased during the rejection phase after OLT (days 7-21) in the DA-PVG combination, while no such response was confirmed in the DA-LEW acute rejection model. Nuclear histone H1 antigens were found in the cytoplasm and the extracellular environment in liver allografts at the rejection phase in the tolerogenic model but not in the rejector model, resulting from the transient induction of anti-histone H1 auto-Ab in recipient PVG rats after OLT. Low dose and short-term immunization with histone H1 upregulated the anti-histone H1 Ab titer in naïve PVG rats, which exhibited a low allogeneic immune response, while no such response was found in naïve LEW rats.

CONCLUSIONS

These results suggest that the sensitivity to nuclear antigens such as histone H1 may be a key factor determining the acceptance or rejection of donor liver grafts, at least in DA-PVG and DA-LEW combinations.

The role of a nuclear protein, histone H1, on signalling pathways for the maturation of dendritic cells

We have demonstrated previously that liver allograft tolerance is associated with the immunosuppressive activity of anti-histone H1 autoreactive antibodies induced in the serum of liver transplantation. Furthermore, we and others have shown that nuclear proteins such as histone H1 and high mobility group box 1 play an important role in maturation of dendritic cells (DCs), although the precise mechanisms are still unknown. In the present study, we focus upon the significance of histone H1 on DCs in terms of the intracellular signalling pathway of DCs. Our immunostaining and immunoblot studies demonstrated that histone H1 was detected in cytoplasm and culture supernatants upon the activation of DCs. Histone H1 blockage by anti-histone H1 antibody down-regulated the intracellular activation of mitogen-activated protein kinases (MAPKs) (p38) and IkappaBalpha of DCs, and inhibited DC activity in the proliferation of CD4+ T cells. On the other hand, the addition of histone H1 without endotoxin stimulation up-regulated major histocompatibility complex class II, the CD80 and CD86 surface markers of DCs and the activation of MAPKs (p38 and extracellular-regulated kinase 1/2) and IkappaBalpha. These results suggest that the translocation of histone H1 from nuclei to cytoplasm and the release of their own histone H1 are necessary for the maturation of DCs and the activation for T lymphocytes.

Development of a two-step chromatography procedure that allows the purification of a high-purity anti-histone H1 monoclonal immunoglobulin M antibody with immunosuppressant activity

In organ transplantation, the development of a novel immunosuppressant free of the need for permanent administration and any serious side effects has eagerly been awaited. We have previously reported that an anti-histone H1 polyclonal antibody has immunosuppressant activity. Here we prepared an anti-histone H1 monoclonal antibody as an analytical tool to elucidate its mechanism of immunosuppression. The isotype of this monoclonal antibody was immunoglobulin M. A monoclonal antibody prepared for administration to organ transplantation model animals should not contain any allogenic proteins and should have high purity. Therefore, we conducted a two-step chromatography procedure, consisting of strong anion-exchange chromatography and gel filtration chromatography, to purify an anti-histone H1 monoclonal immunoglobulin M antibody from the serum-free culture supernatant of hybridomas. Consequently, we successfully purified the monoclonal antibody at 96%, a purification rate at which its administration to organ transplantation model animals is possible.

Experimental and clinical significance of antinuclear antibodies in liver transplantation

Histone H1 and high-mobility group box 1 (HMGB1) proteins are known to initiate an immune reaction, and the corresponding antibodies (Abs) possess immunosuppressive activity. In the present study, we aimed to evaluate the immunological role of antinuclear Abs in experimental and clinical liver transplantation. In a rat tolerogenic orthotopic liver transplantation (OLT) model, antihistone H1 and HMGB1 titers were induced during the rejection and tolerance induction phases, respectively. Those Ab responses also were confirmed in a drug-induced tolerance model (acute rejection model + cyclosporin A [0 to 14 days after OLT]). We also found a similar tendency in our clinical drug-free patient (who experienced complete cessation of any immunosuppressive treatments) and that antinuclear Abs induced in the serum after cessation of immunosuppressants play a part of immune privilege in this patient. These results suggest that antinuclear Abs are important factors for overcoming rejection and the subsequent tolerance induction in liver transplantation.

Histone H1 vaccine therapy for overcoming acute rejection in experimental organ transplantation

OBJECTIVE

In a rat tolerogenic orthotopic liver transplantation (OLT) model, the recipient serum (post-OLT serum) shows strong immunosuppressive activity. In our previous reports, we suggested that autoreactive antibody (Ab) against histone H1 is a major immunosuppressive factor in this serum. The present study sought to determine whether up-regulation of anti-histone H1 Ab by histone H1 vaccination led to tolerance.

MATERIALS AND METHODS

Using mixed lymphocyte reactions (MLR) and heterotopic heart transplantations (HHT), the alloreactive T-cell responses and allograft survivals of histone H1-immunized rats were compared with those of control rats. Cytokine and cellular profiles were determined by enzyme-linked immunosorbent assay (ELISA) and flow cytometry.

RESULTS

The alloreactive T-cell response of histone H1-immunized rats was significantly lower than that of control rats, although there was no difference in nonspecific T-cell activation between the 2 groups. The allograft survival of histone H1-immunized rats was significantly prolonged after HHT. The major histocompatibility complex (MHC) class II and CD25 molecules of histone H1-immunized rats were significantly down-regulated compared with those of control rats. Moreover, the serum cytokine profile was modified by the immunization with histone H1.

CONCLUSIONS

These results suggest that histone H1 vaccination of transplant recipients leads to the production of immunosuppressive factors and the modification of cytokine/cellular profiles.

The immunological role of lipid transfer/metabolic proteins in liver transplantation tolerance

BACKGROUND

In a rat tolerogenic orthotopic liver transplantation (OLT) model, recipient serum after OLT (post-OLT serum) has been reported to prevent allograft rejection. A previous proteomic study indicated that apolipoprotein E (apo-E), which is an important factor for cholesterol transportation, is expressed at the latter tolerogenic phase after OLT. It has also been known that adipose tissue-derived adipokine, adiponectin, is an essential factor for fatty acid catabolism. This study aimed to characterize the role of lipid transfer/metabolic proteins in liver transplantation tolerance.

METHODS

To identify the apo-E and adiponectin in post-OLT serum, Western analyses and enzyme-linked immunosorbent assay (ELISA) were performed, respectively. The immunosuppressive activities of those factors were evaluated by inhibition of the mixed lymphocyte reaction (MLR).

RESULTS

Western analyses showed that the mobility of apo-E was shifted at the latter tolerogenic phase after OLT in a natural tolerance model, and a similar phenomenon was confirmed in the serum of a drug-induced tolerance model (rejection model+cyclosporin A (CsA); 0 to 14 days) after cessation of CsA. Further study revealed that neutralization of modified apo-E in post-OLT serum reduced the immunosuppressive activity. Additionally, plasma adiponectin was significantly elevated at the latter phase after OLT, and possessed MLR-inhibitory activity.

CONCLUSIONS

These results suggest that the mobility shift of apo-E and/or the up-regulation of adiponectin may be necessary for overcoming the rejection, recovering the liver allograft function, and following tolerance induction in experimental OLT models, and may be useful as one indicator to surmise the prognosis after liver transplantation.

Impact of vaccine therapy using nuclear histone H1 on allograft survival in experimental organ transplantation

BACKGROUND

We recently reported that autoreactive antibody (Ab) against nuclear histone H1 had been identified as an immunosuppressive factor in a rat tolerogenic orthotopic liver transplantation (OLT) model. The present study aimed to determine whether the up-regulation of antihistone H1 Ab by histone H1 vaccination leads to tolerance.

METHODS

Histone H1-immunized rats were established by intraperitoneal vaccination with histone H1 at every two-weekly interval. By using mixed lymphocyte reaction (MLR) and heterotopic heart transplantation (HHT), the alloreactive T cell response and allograft survival of histone H1-immunized rats were compared with those of control rats. Cytokine and cellular profiles in histone H1-immunized rats were determined by reverse transcriptase polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and flow cytometry.

RESULTS

Immunization with histone H1 in Freund's adjuvant induced alloreactive T cell unresponsiveness and prolonged heterotopic heart allograft survival. It also down-regulated the expression of major histocompatibility complex (MHC) class II and CD25 on splenic cells, elevated the T helper cell type 2 (Th2) skewing index (Interleukin (IL)-4/interferon (IFN)-gamma ratio or IL-4/IL-2 ratio) and modified the serum cytokine profiles.

CONCLUSIONS

The present results suggest that histone H1 vaccination of transplant recipients, which leads to the production of immunosuppressive factor and the modification of the cytokine/cellular profiles, has great potential as a tolerance therapy for prospective transplantation.

Beyond the walls of the nucleus: the role of histones in cellular signaling and innate immunity

Although they are one of the oldest family of proteins known (first described in 1884 by Kossel), histones continue to surprise researchers with their ever expanding roles in biology. In the past 25 years, the view of core histone octamers as a simple spool around which DNA in the nucleus is wound and linker histones as mere fasteners clipping it all together has transformed into the realization that histones play a vital role in transcriptional regulation. Through post-translational modifications, histones control the accessibility of transcription factors and a host of other proteins to multiple, conceivably thousands of, genes at once. While researchers have spent decades deciphering the role of histones in the overall structure of chromatin, it might surprise some to find that an entirely separate faction of scientists have focused on the role of histones beyond the confines of the nuclear envelope. In the past decade, there has been an accumulation of observations that suggest that histones can be found at the mitochondrion during the onset of apoptotic signaling and even at the cell surface, acting as a receptor for bacterial and viral proteins. More provocatively, immunologists are becoming convinced that they can also be found in the lumen of several tissues, acting as antimicrobial agents--critical components of an ancient innate immune system. Perhaps nowhere is this observation as dramatic as in the ability of neutrophils to entrap bacterial pathogens by casting out "nets" of DNA and histones that not only act as a physical barrier, but also display bactericidal activity. As our views regarding the role of histones inside and outside the cell evolve, some have begun to develop therapies that either utilize or target histones in the fight against cancer, microbial infection, and autoimmune disease. It is our goal here to begin the process of merging the dichotomous lives of histones both within and without the nuclear membrane.

Role of Antinuclear Antibodies in Experimental and Clinical Liver Transplantation

OBJECTIVE

We recently reported that autoreactive antibodies (Abs) against nuclear histone H1 was transiently induced at an early phase after orthotopic liver transplantation (OLT) in a tolerogenic rat OLT model and possessed immunosuppressive activity. It was also reported that nuclear antigen, high-mobility group box 1 (HMGB1) protein was one of the initiators of the immune reaction. The present study sought to evaluate the role of antinuclear Abs in experimental and clinical liver transplantation.

MATERIALS AND METHODS

We prepared 3 animal models: natural tolerance model (DA liver into PVG); acute rejection model (DA liver into LEW); and drug-induced tolerance model (acute rejection model + cyclosporine [CsA]). In addition, we examined clinical samples, including 1 drug-free patient, to measure the antihistone H1/HMGB1 titers at various times after OLT.

RESULTS

In a natural tolerance model, antihistone H1 and HMGB1 Ab was induced during the rejection and the tolerance induction phases, respectively. Those Ab responses were also confirmed in a drug-induced tolerance model, whereas no such responses were shown in an acute rejection model. In our clinical drug-free patient, antihistone H1/HMGB1 titer was significantly higher after cessation of CsA than that in healthy volunteers.

CONCLUSIONS

Antinuclear Ab is actively expressed in accordance with overcoming rejection episodes with subsequent tolerance induction in both a natural tolerance model and a drug-induced tolerance model. We also observed a similar tendency in our clinical drug-free patient. These results suggested that antinuclear Abs may be useful markers to determine the timing to withdraw immunosuppressants.

Differential regulation of proteasome activity in the nucleus and the synaptic terminals

Proteasome is a multi-subunit proteolytic complex that degrades proteins covalently linked to multiple molecules of ubiquitin. Earlier studies showed a role for the ubiquitin-proteasome pathway in several models of long-term memory and other forms of synaptic plasticity. In Aplysia, the ubiquitin-proteasome pathway has been shown to contribute to the induction of long-term facilitation. In other model systems, ubiquitin-proteasome-mediated proteolysis has also been shown to play a role in synapse development. Previous studies of synaptic plasticity focused on changes in components or the substrates of the ubiquitin-proteasome pathway in whole neurons. Modification of specific synapses would require precise spatial and temporal regulation of the components of the ubiquitin-proteasome pathway within the subcellular compartments of neurons during learning. As a first step towards testing the idea of local regulation of the ubiquitin-proteasome pathway in neurons, we investigated proteasome activity in nuclear and synaptosomal fractions. Here we show that proteasome activity in the synaptic terminals is higher compared to the activity in the nucleus in the Aplysia nervous system as well as in the mouse brain. Furthermore, the proteasome activity in the two neuronal compartments is differentially modulated by protein kinases. Differential regulation of proteasome activity in neuronal compartments such as the synaptic terminals is likely to be a key mechanism underlying synapse-specific plasticity.

The effects of anti-histone H1 antibody on immune cells responsible for rejection reaction

We previously demonstrated the immunosuppressive activity of anti-histone H1 autoreactive antibodies (Ab) transiently induced in serum of a rat tolerogenic orthotopic liver transplantation (OLT) model. In the present study, we investigated the effects of anti-histone H1 Ab on dendritic cells (DCs), T-cells, lymphokine-activated killer (LAK) cells, and human natural killer (NK) cells. The effects of anti-histone H1 Ab on Concanavalin A (ConA) blast, on rat DC cytokine profiles and phenotypes, and on T-cells, LAK cells, and human NK cells were examined by flow cytometry and RT-PCR. The cytotoxicity of LAK and NK cells pretreated with anti-histone H1 Ab was assayed. The addition of anti-histone H1 Ab to ConA blast inhibited the proliferation of 5-(6)-carboxy-fluorescein succinimidyl ester (CFSE)-labeled lymphocytes without toxicity but increased the population of CD4+CD25+ T-cells. DCs treated with anti-histone H1 Ab expressed lower levels of CD80/CD86, IL-1beta, and IL-6. The addition of anti-histone H1 Ab to LAK culture decreased the percentages of NKR-P1 populations and down-regulated levels of inducible nitric oxide synthase (iNOS), IL-2, and INF-gamma in RT-PCR. The cytotoxicity of LAK and NK cells was lower when pretreated with anti-histone H1 Ab than when pretreated with control IgG. We found that the blockade of histone H1 modulated DCs toward tolerogenic status, decreased the cytotoxicity of LAK and NK cells, and induced CD4+CD25+ T-cells. These results suggest that the use of anti-histone H1 Abs might be a useful strategy for the development of a form of immunosuppression.

Characterization of immunosuppressive factors expressed in serum by rat tolerogenic liver transplantation

BACKGROUND

In a rat tolerogenic model of orthotopic liver transplantation (OLT), recipient serum after OLT (post-OLT serum) possesses strong immunosuppressive activity. This study aimed to identify immunosuppressive factors present in early post-OLT serum.

METHODS

Immunosuppressive activity was evaluated in vitro by inhibition of the mixed-lymphocyte reaction (MLR). Autoantigens recognized by MLR-inhibitory IgG were identified by the internal protein sequencing.

RESULTS

Recipient post-OLT serum inhibited MLR, and OLT-inducible IgG was the major immunosuppressive factor. IgG from post-OLT sera (2 to 3 weeks) specifically reacted to 31; 34; and 73-kd autoantigens on spleen cells. The internal sequences of the 31- and 34-kd antigens coincided completely with those of histone H1 molecules. Immunodepletion of anti-histone H1 antibodies (Abs) from early post-OLT serum abolished the MLR-inhibitory activity. Furthermore, rabbit polyclonal Ab-directed histone H1 not only significantly suppressed rat and human MLR but also prolonged survival of heart allografts. Flow-cytometric analysis revealed that some live PVG splenocytes were stained with antihistone H1 Abs, and that these positive cells increased on Con A stimulation. Western blot analysis indicated that several cross-reactive antigens against anti-histone H1 Abs were found in their membrane fraction.

CONCLUSIONS

In this study we provide evidence that autoreactive Abs, against histone H1 are a major OLT-induced graft survival factor, and may play at least a part in overcoming the acute rejection phase to establish solid allograft tolerance.