Comparative analysis of the fate of donor dendritic cells and B cells and their influence on alloreactive T cell responses under tacrolimus immunosuppression

We have shown that tacrolimus (TAC)-induced liver allograft acceptance is associated with migration and persistence of donor B cells and dendritic cells (DC). To clarify whether these MHC class II+ leukocytes have favorable roles in inducing tolerance, we analyzed recipient T cell reactions after allogeneic B or DC infusion. LEW rat B cells localized exclusively in BN host B cell follicles without any direct contact with host T cells. While few donor DC migrated to T cell areas and marginal zones, they were captured by host APC, suggesting that allogeneic MHC class II+ cells may induce immune reactions via the indirect pathway. Although DC-infused non-immunosuppressed recipients showed enhanced ex vivo anti-donor responses, persistent in vitro donor-specific hyporeactivity was seen equally with donor DC or B cell infusion under TAC. The results indicate that donor MHC class II+ APC are capable of regulating recipient immune reactions under TAC. Possible involvement of the indirect pathway of allorecognition is discussed.     

Dual effects of the alloresponse by Th1 and Th2 cells on acute and chronic rejection of allotransplants

The contribution of direct and indirect alloresponses by CD4⁺ Th1 and Th2 cells in acute and chronic rejection of allogeneic transplants remains unclear. In the present study, we addressed this question using a transplant model in a single MHC class I‐disparate donor–recipient mouse combination. BALB/c‐dm2 (dm2) mutant mice do not express MHC class I L^d molecules and reject acutely L^d+ skin grafts from BALB/c mice. In contrast, BALB/c hearts placed in dm2 mice are permanently accepted in the absence of chronic allograft vasculopathy. In this model, CD4⁺ T cells are activated following recognition of a donor MHC class I determinant, L^d 61–80, presented by MHC Class II A^d molecules on donor and recipient APC. Pre‐transplantation of recipients with L^d 61–80 peptide emulsified in complete Freund's adjuvant induced a Th1 response, which accelerated the rejection of skin allografts, but it had no effect on cardiac transplants. In contrast, induction of a Th2 response to the same peptide abrogated the CD8⁺ cytotoxic T cells response and markedly delayed the rejection of skin allografts while it induced de novo chronic rejection of heart transplants. This shows that Th2 cells activated via indirect allorecognition can exert dual effects on acute and chronic rejection of allogeneic transplants.     

Inflammation in sympathetic ganglia proximal to sciatic nerve transection in rats

Comparison was made between recruitment of T-lymphocytes and macrophages into lumbar sympathetic ganglia (SGs) and dorsal root ganglia (DRGs) following sciatic nerve transection in rats. In both control and lesioned SGs, resident (ED2+) macrophages expressed less major histocompatibility complex class II (MHC II), but MHC II+ macrophage density was higher, than in equivalent DRGs. The influx of T-cells was larger and the influx and activation of macrophages were more sustained in SGs than in DRGs. Only two of the five subtypes of macrophage that invade lesioned DRGs were recruited to SGs. While some MHC II+ cells phagocytosed dead sympathetic neurones, most phagocytes in SGs lacked a macrophage marker. The different patterns of response between ganglia may provide clues about macrophage involvement in neuronal death and hyperexcitability after peripheral nerve lesions.     

Macrophages in experimental rat lung isografts and allografts: infiltration and proliferation in situ

Alveolar macrophages (AMs) and peribronchial/perivascular macrophages are probably involved in lung allograft damage. We investigate leukocyte infiltration into graft tissue and address the question whether proliferation in situ contributes to macrophage homeostasis and accumulation. Lung transplantation was performed in the Lewis (LEW)-to-LEW and in the Dark Agouti-to-LEW rat strain combination. Graft infiltration by ED1+ and ED2+ (CD163) macrophages was analyzed by immunohistochemistry (IHC) and compared with infiltration by lymphocytes. Cells in the S-phase of the cell cycle were pulse-labeled with BrdU and detected immunohistochemically. Finally, the donor or recipient origin of AMs was determined by IHC and in situ hybridization. ED1+ AMs in allogeneic transplants increased by more than 25-fold from Days 1 to 5. In addition, large, peribronchial/perivascular infiltrates developed containing numerous ED1+ cells. Although AMs in normal rat lungs are CD163-, AMs up-regulated CD163 between Days 4 and 5, reaching maximum values on Day 6. Lymphocytes were less numerous than macrophages. About 16% of the AMs and 10% of the peribronchial/perivascular macrophages were in the S-phase of the cell cycle on Day 2 post-transplantation. No differences in the frequency of BrdU+ macrophages were obvious between isografts and allografts. AMs of donor origin increased in number considerably during allograft rejection. In conclusion, the cellular infiltrate in lung allografts is dominated by macrophages, which exhibit an unusual phenotype and a strong capacity for mitotic self-renewal.     

Dendritic cells, but not macrophages or B cells, activate major histocompatibility complex class II-restricted CD4+ T cells upon immune-complex uptake in vivo

Professional antigen-presenting cells (APC) are able to process and present exogenous antigen leading to the activation of T cells. Antigen-immunoglobulin (Ig)G complexes (IC) are much more efficiently processed and presented than soluble antigen. Dendritic cells (DC) are known for their ability to take up and process immune complex (IC) via FcgammaR, and they have been shown to play a crucial role in IC-processing onto major histocompatibility complex (MHC) class I as they contain a specialized cross-presenting transport system required for MHC class I antigen-processing. However, the MHC class II-antigen-processing pathway is distinct. Therefore various other professional APC, like macrophages and B cells, all displaying FcgammaR, are thought to present IC-delivered antigen in MHC class II. Nonetheless, the relative contribution of these APC in IC-facilitated antigen-presentation for MHC class II in vivo is not known. Here we show that, in mice, both macrophages and DC, but not B cells, efficiently capture IC. However, only DC, but not macrophages, efficiently activate antigen-specific MHC class II restricted CD4(+) T cells. These results indicate that mainly DC and not other professional APC, despite expressing FcgammaR and MHC class II, contribute significantly to IC-facilitated T cell activation in vivo under steady-state conditions.     

移植心Th细胞免疫偏离与MHC Ⅱ类抗原表达的关系

目的:探讨Th细胞免疫偏离与移植心MHC Ⅱ类抗原表达的关系。方法:建立大鼠心脏移植模型,以同系移植和无移植动物作为对照,采用逆转录PCR技术测定移植心Ⅰ、Ⅱ类细胞因子IL-2、IL-4 mRNA水平变化,用免疫组化技术和单克隆抗体测定移植心MHC Ⅱ类抗原表达。结果:IL-2 mRNA水平和MHC Ⅱ类抗原表达随着移植心急性免疫排斥病变发展而显著增加(P＜0.01), IL-4 mRNA水平则显著降低(P＜0.01),急性免疫排斥发展到一定阶段Ⅰ、Ⅱ类细胞因子水平出现偏离时MHC Ⅱ类抗原由低表达变为高表达。结论:移植心脏急性免疫排斥过程中,Th细胞免疫偏离与MHC Ⅱ类抗原表达变化有相关性,并参与促进移植心脏MHC Ⅱ类抗原的高表达。     

Vesicles bearing MHC class II molecules mediate transfer of antigen from antigen-presenting cells to CD4+ T cells

Previous studies have provided evidence that myelin basic protein (MBP)-specific rat T cells acquire antigen via transfer of preformed peptide/MHC class II complexes from splenic antigen-presenting cells (APC). The purpose of the present study was to determine how T cells acquire peptide/MHC class II complexes from APC in vitro. Our results show that a MHC class II+ T cell line, R1-trans, released MHC class II-bearing vesicles that directly stimulated MBP-specific CD4+ T cells. Vesicles expressing complexes of MHC class II and MBP were also specifically cytotoxic to MBP-specific T cells. Surviving T cells acquired MHC class II/antigen complexes from these vesicles by a mechanism that did not require protein synthesis but depended on specific TCR interactions with peptide/self MHC complexes. Furthermore, MBP/MHC class II-bearing vesicles enabled T cells to present MBP to other T cell responders. These studies provide evidence that APC release vesicles expressing preformed peptide/MHC class II complexes that interact with clonotypic TCR, allowing MHC class II acquisition by T cells. Vesicular transport of antigen/MHC class II complexes from professional APC to T cells may represent an important mechanism of communication among cells of the immune system.     

The nature and mechanisms of DN regulatory T-cell mediated suppression

Regulatory T cells have been reported to enhance survival of transplanted allografts. We have recently identified and cloned a novel CD3(+)CD4(-)CD8(-) (double negative, DN) regulatory T cell from mice that were given a single class I mismatched donor lymphocyte infusion and permanently accepted donor-specific skin allografts. When infused into na?ve syngeneic mice, these DN T cells prolonged the survival of class I mismatched donor skin allografts. Here we further characterize the nature and mechanism of DN T-cell mediated suppression. This present study reveals that DN T cells are able to specifically eliminate activated syngeneic CD8(+) T cells that share the same T cell receptor (TCR) specificity as DN T cells in vitro. Similarly, we found that, along with an increase of recipient DN T cells in the peripheral blood, anti-donor CD8(+) T cells were also eliminated in vivo following a donor lymphocyte infusion. We further demonstrate that DN T regulatory cells do not mediate suppression by competition for growth factors or antigen presenting cells (APC) nor by modulation of APC, but require cell contact with the activated target CD8(+) T cells. This contact can be mediated either by the TCR on CD8(+) T cells that recognize constitutively expressed or acquired MHC molecules on DN T cells, or by the TCR on DN T cells that recognize constitutively expressed MHC molecules on CD8(+) T cells. Together, these data extend our previous findings, and expand the conditions in which DN T cells can potentially be used to specifically suppress allogeneic immune responses.     

Masking of veto function in vivo by activated CD4+ T lymphocytes

Donor CD8+ T lymphocytes injected into recipient mice incompatible at major histocompatibility complex (MHC) class I genes induce donor-specific CTL nonresponsiveness, attributed to the veto function of donor cells. Here we show that conditions leading to strong activation of CD4+ T cells, namely the presence in the recipient of foreign MHC class II determinants, lead to the apparent loss of veto function of donor cells. This "masking" of veto function is dependent on the dose of foreign MHC class II present. Veto function can be partially restored by treatment of recipients in vivo with CD4-specific antibody, a measure which has been shown to eliminate the function of CD4+ T cells in vivo. We conclude that CD4+ T cells activated by contact with antigen can interfere with the veto function of CD8+ T cells. Consequences of this finding are: (a) veto function of a sample cell population can be overlooked when activation of CD4+ T cells occurs simultaneously. (b) The balance between veto function of recipient cells and its abrogation might be responsible for the kind of graft-vs.-host reaction generated (CD8+ T cell-mediated and frequently lethal or CD4+ T cell-mediated and not lethal) when parental T cells are injected into recipients incompatible at MHC class I and class II genes. (c) A possible contribution of veto cells should be considered in several protocols in which donor hemopoetic cells were used in conjunction with CD4-specific antibodies to induce transplantation tolerance. (d) Veto function in vivo does not require a contribution of CD4+ T cells.     

Tertiary lymphoid organs in renal allografts can be associated with donor-specific tolerance rather than rejection

Tertiary lymphoid organs can form at sites of chronic inflammation. Their presence has been mainly associated with tissue destruction. In transplantation, there is a dynamic immune response as in chronic inflammation. Indeed, the presence of tertiary lymphoid organs has been associated with chronic rejection. In addition to a destructive alloimmune response, secondary lymphoid organs are also important in transplant tolerance. We hypothesised that tertiary lymphoid organs may also form during transplantation tolerance as this process also requires an active local immune response. If so, their presence may enhance tolerance, resulting in better graft function rather than chronic rejection. Using a mouse kidney allograft model of tolerance, we demonstrate the formation of tertiary lymphoid organs within tolerated allografts. Tertiary lymphoid organs are supplied by high endothelial venules, and contain T and B cells, macrophages, DC, Foxp3(+) T cells, donor MHC class II(+) cells and recipient cells presenting donor-derived allopeptides. Formation of tertiary lymphoid organs and the presence of immune cells within them are associated with superior graft function, suggesting that tertiary lymphoid organs act to amplify the prevailing immune response, be it a tolerant and beneficial immune response or the previously described destructive alloimmunity.     

Phenotypic analysis of IL-10-treated macrophages using the monoclonal antibodies RFD1 and RFD7.

Suppressive or tolerogenic antigen-presenting cells (APC) might play an important role in the control of auto/hyperreactivity and the resolution of the immune response. Recent studies have provided evidence that tolerogenic APC can be induced by anergic T cells or interleukin-10 (IL-10). The aim of this study is to investigate how anergic T cells and IL-10 induce the suppressive APC phenotype and how this affects the immune response. Previously, two monoclonal antibodies (RFD1 and RFD7) were described by our lab which distinguish inductive (RFD1+RFD7-), phagocytic (RFD1-RFD7+) and suppressive (RFD1+RFD7+) macrophages. RFD1 recognizes an MHC class II-associated epitope which has restricted expression, and RFD7 recognizes a predominantly cytoplasmic antigen. Macrophages were derived from the adherent fraction of peripheral blood mononuclear cells from healthy donors. At day 5, IL-10 or IFNgamma (a cytokine which should lead to the inductive APC phenotype) was added to the cultures. At day 7, the macrophages were harvested and their phenotypes were assessed by immunohistochemical staining and FACS analysis. Upon culture of macrophages with IL-10 RFD1 staining and HLA class II expression were reduced, whereas RFD7 staining was increased. Incubation of APC with IFNgamma led to upregulation of RFD1 and HLA class II, without affecting RFD7 staining. This suggests that IL-10 induced the suppressive RFD1+RFD7+ APC population, whereas IFNgamma treatment led to the inductive RFD1+RFD7- APC subset. Thus the use of IL-10 and/or IFNgamma, and the discrimination offered by mAbs RFD7 and RFD1 represent a model whereby APC function in terms of T cell stimulation or T cell anergy can be assessed.     

Differential expression of major histocompatibility complex class Ia, Ib, and II molecules on monocytes-derived dendritic and macrophagic cells.

Blood monocyte derived antigen presenting cells (APC) such as dendritic cells and macrophages are considered as major promising tools for antitumoral immunotherapy. In order to contribute to their phenotype characterization, we have precisely investigated their levels of expression of MHC class Ia, Ib (HLA-G) and II molecules using mainly flow cytometry quantification assays. APC were generated from monocytes cultured for 7 days in the presence of GM-CSF and IL-4 or M-CSF. These cells, which exhibited known morphological and immunological features of dendritic cells and macrophages respectively, were evidenced to display high expression of MHC class Ia and class II antigens in comparison to that found in monocytes. Dendritic cells and macrophages thus expressed 2-fold more and 4-fold more MHC class Ia molecules and 5-fold and 3-fold more MHC class II DR molecules than parental monocytes. In addition, expression of MHC class II DP and DQ molecules, not or only barely detected in monocytes, was clearly demonstrated in the two kinds of APC. In contrast, monocytes, dendritic cells and macrophages failed to express MHC class Ib HLA-G antigen. The up-regulation in monocyte-derived APC of MHC class Ia and II molecules mediating the presentation of antigen peptides to lymphocytes fully supports the interest of such APC in antitumoral immunotherapy.     

Mucosal delivery of CpG oligodeoxynucleotides expands functional dendritic cells and macrophages in the vagina

Antigen-presenting cells (APC) are specialized sentinel cells that sense pathogens within tissues and then activate appropriate immune effector cells in lymphoid organs. Recent evidence, however, suggests that APC can also induce effector cells in non-lymphoid organs. The purpose of this study was to determine the effect of intravaginal (IVAG) delivery of CpG-oligodeoxynucleotide (ODN) on expansion of resident genital APC. Our results show that delivery of CpG-ODN to the murine genital tract induced a rapid and significant, but transient expansion of genital APC in situ. As early as 12 hr post CpG-ODN delivery, we observed an enhanced level of F4/80+ major histocompatibility complex (MHC) class II-negative macrophages in the genital tissue. This was followed by increased levels of F4/80/MHC class II double-positive cells, as well as MHC class II, CD11c and CD86 triple-positive dendritic cells (DC) at 48 hr. Expanded APC levels at 48 hr post CpG-ODN resulted in increased ability of genital cells to induce an allogenic mixed leucocyte reaction. By 72 hr after CpG-ODN treatment, APC levels were not distinguishable from naive levels. Therefore, these results clearly show that administration of CpG-ODN to the genital tract induced a marked but transient enhancement of APC within the genital tissue, and that these APC appear to possess functional capacity. Furthermore, these results indicate that IVAG-CpG-ODN may be an important factor for the enhancement of local antigen presentation in the genital tract through increased DC numbers.     

Analysis of the immune response induced by a single xenoantigen in vivo

Transgenic mice expressing human major histocompatibility complex (MHC) class II molecules would provide a valuable model system for studying murine anti-human MHC immune response. We have previously shown that skin from HLA-DR1 transgenic mice was rejected by control littermates and spleen cells from rejecting mice were able to proliferate to donor cells. The aim of this paper is to analyze the mechanism of recognition of this xenoantigen and the possible involvement of antibody response in anti-HLA-DR1 immune response. Control littermates were immunized with spleen cells from HLA-DR1 transgenic (TG) mice; at indicated times, xenoantigen-specific proliferation and IFNgamma production was assessed using APC obtained from HLA-DR1 TG mice. Mixed direct-indirect pathway of xenoantigen recognition was suggested by the following findings: i)T cell response to HLA-DR1 was inhibited adding in culture monoclonal antibodies directed either to donor (HLA-DR) or to recipient MHC (I-A); ii) APC from control mice pulsed with purified DR1 molecules were able to induce proliferation by FVB/N mice immunized with transgenic spleen cells. HLA-DR1 recognition permits DR peptide-specific T cell response by lymphocytes of control littermates immunized with the xenoantigen. In addition, we detected xenoreactive IgM and IgG2 antibodies. Our data suggest that HLA-DR1 xenoantigen may be recognized through direct or indirect pathway and provide additional information on mouse anti-human HLA immune response.     

Rat thymic cultures: morphological and phenotypical characterization

Rat thymic cultures have been established in order to analyse the morpho-functional characteristics of thymic epithelial and non-epithelial cells in vitro. Stromal cultures, originating from implanted thymic fragments, consist of fibroblasts occupying most of the culture surface, epithelial cells forming discrete colonies, thymocytes and bone marrow-derived cells. Epithelial cells show a low class II MHC antigen expression, which is highly increased in semi-adherent cells, and do not interact with thymocytes. Thymocytes proliferate extensively at the beginning of the culture, but almost disappear at the end of the first week; however, restarting of thymocyte proliferation occurs during the second week of culture. Bone marrow-derived cells include ED- Ia+ CR3- IL-2R- dendritic cells (DC), ED+ Ia+ CR3+ IL-2R+ non-adherent thymic phagocytic cells (PTR) and ED+ Ia- CR3- IL-2R- adherent type 1 and 2 macrophages, derived from PTR. Both PTR and DC establish lympho-stromatic complexes with thymocytes present in the cultures. These results suggest that PTR and DC present in rat thymic cultures belong to different cell lineages, and that they are, respectively, the in vitro equivalents of intrathymic macrophages and interdigitating cells.     

Identification of T cell subsets and class I and class II antigen expression in islet grafts and pancreatic islets of diabetic BioBreeding/Worcester rats

The BioBreeding/Worcester (BB/Wor) rat develops a spontaneous disorder that closely resembles human insulin-dependent (Type I) diabetes mellitus. The syndrome is preceded by lymphocytic insulitis that destroys pancreatic beta cells. The morphologic features of the spontaneous insulitis lesions are also observed within islets transplanted beneath the renal capsule of diabetes-prone and diabetic animals. This study reports the results of experiments in which immunohistochemical techniques were used to characterize the phenotype of the infiltrating mononuclear cells and detect the expression of class I and class II MHC antigens in native islets and islet transplants in diabetic and diabetes-prone BB/Wor rats. The infiltrates within native pancreatic islets and islet grafts were comprised predominantly of Ia+ cells (dendritic cells and macrophages) CD4+ cells (helper/inducer lymphocytes and macrophages), CD5+ (pan-T) cells and smaller numbers of CD8+ (cytotoxic/suppressor and NK) cells. Pancreatic and graft insulitis were accompanied by markedly enhanced class I antigen expression on islet and exocrine cells. Class II (Ia) antigens were not detected on normal islet cells, islets undergoing insulitis or on islet transplants subjected to immune attack. In islet grafts stained with polymorphic MAbs that distinguish Ia antigens of donor and host origin, Ia antigen expression was limited to infiltrating dendritic cells and macrophages of host origin. It is concluded that the phenotypes of infiltrating mononuclear cells that comprise the insulitis lesion in spontaneous BB/Wor diabetes, and the inflammatory attack on islets transplanted into diabetic BB/Wor rats are the same, that pancreatic islet and graft insulitis occur in the presence of enhanced class I antigen expression but in the absence of class II antigen expression, and that infiltrating Ia+ cells within islet grafts are exclusively of recipient (BB/Wor) origin and may explain the initiation of immune insulitis within grafts derived from donors of incompatible MHC.     

胚胎干细胞源性神经前体细胞移植脑缺血大鼠局部细胞的免疫反应

背景：神经前体细胞的免疫原性各家研究结果不一,尤其是体内移植后的机体免疫反应模式需要进一步研究。 目的：体外观察神经前体细胞组成型及诱导型主要组织相容性抗原表达情况;体内观察神经前体细胞移植入大鼠脑缺血组织后局部免疫细胞活化情况,探讨神经前体细胞的移植排斥可能性及模式。 方法：自pCX-hrGFP ES-D3胚胎干细胞诱导分化神经前体细胞,流式细胞术体外检测主要组织相容性抗原Ⅰ,Ⅱ类分子表达及γ-干扰素诱导前后表达变化。实验分3组,磷酸盐缓冲液组、神经前体细胞组分别于大脑中动脉缺血大鼠模型造模后经侧脑室给予磷酸盐缓冲液注射及神经前体细胞移植,假手术组不造模。免疫组化法观察纹状区ED1+、CD4+、CD8+细胞浸润情况;淋巴细胞再刺激增殖实验观测神经前体细胞诱导移植大鼠颈部淋巴细胞的增殖指数。 结果与结论：神经前体细胞组成型高表达主要组织相容性抗原Ⅰ类分子,几乎不表达主要组织相容性抗原Ⅱ类分子;经γ-干扰素诱导后,主要组织相容性抗原Ⅰ类分子进一步上调,主要组织相容性抗原Ⅱ类分子亦有轻度上调,提示神经前体细胞有可能引起机体免疫反应。移植实验表明,与假手术组相比,磷酸盐缓冲液组及神经前体细胞组均表现强烈的ED1+、CD4+、CD8+细胞浸润(P < 0.05),说明脑缺血损伤本身能导致局部免疫细胞活化;神经前体细胞组比磷酸盐缓冲液组有更强的ED1+、CD4+细胞浸润(P < 0.05),提示神经前体细胞移植可能导致局部免疫更进一步活化,且以CD4+T细胞反应为主。磷酸盐缓冲液组及神经前体细胞组神经前体细胞诱导下的增殖指数值均较假手术组升高(P < 0.01),但前两组增殖指数值比较差异无显著性意义(P > 0.05),提示脑组织局部炎症导致颈部淋巴细胞增殖性增加,而离体神经前体细胞不足以单独刺激致敏淋巴细胞增殖。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

Luminal bacterial antigen-specific CD4+ T-cell responses in HLA-B27 transgenic rats with chronic colitis are mediated by both major histocompatibility class II and HLA-B27 molecules

Rats transgenic (TG) for the human major histocompatibility complex (MHC) class I HLA-B27 and beta2-microglobulin genes develop chronic colitis under specific pathogen-free (SPF) but not sterile (germ-free, GF) conditions. We investigated the role of antigen-presenting molecules involved in generating immune responses by CD4+ mesenteric lymph node (MLN) cells from colitic HLA-B27 TG rats to commensal enteric micro-organisms. All TG MLN cells expressed HLA-B27. A higher level of MHC class II was expressed on cells from TG rats, both SPF and GF, compared to non-TG littermates. In contrast, rat MHC class I expression was lower on TG than non-TG cells. Both TG and non-TG antigen presenting cells (APC) pulsed with caecal bacterial antigens induced a marked interferon-gamma (IFN-gamma) response in TG CD4+ T lymphocytes but failed to stimulate non-TG cells. Blocking MHC class II on both TG and non-TG APC dramatically inhibited their ability to induce TG CD4+ T cells to produce IFN-gamma. Blocking HLA-B27 on TG APC similarly inhibited IFN-gamma responses. When the antibodies against MHC class II and HLA-B27 were combined, no APC-dependent IFN-gamma response was detected. These data implicate both native rat MHC class II and TG HLA-B27 in CD4+ MLN T-cell IFN-gamma responses to commensal enteric microflora in this colitis model.     

Exogenous CLIP localizes into endocytic compartment of cells upon internalization: implications for antigen presentation by MHC class II molecules

We have previously shown that exogenous CLIP (class II associated invariant chain peptide) downregulated MHC class II expression on antigen presenting cells (APC) and modulated T cell mediated immune responses. The present study was undertaken to investigate the mechanism of uptake of exogenously added CLIP peptide by APC. We found that exogenous CLIP is rapidly internalized by APC and it co-localize with MHC class II in intracellular compartments including early-, late-endosomes and lysosomes. We suggest that exogenous CLIP acts as an in vivo regulator of immune response by internalization and passage through the intracellular compartments where it interferes in peptide loading and recycling of MHC class II molecules to the APC surface. Therefore, exogenous CLIP regulates immune responses by modulation of antigen presentation by the APC.     

Crucial Fas-Fas ligand interaction in spontaneous acceptance of hepatic allografts in mice

The Fas/Fas ligand (FasL) system plays important roles in the immune system, including host immunoregulation and cytotoxicity. In this study, we investigated the involvement of Fas-FasL interactions in spontaneous acceptance of hepatic allografts in murine orthotopic liver transplantation. Liver transplantation between the C57BL/6 (B6, H-2b) donor and the MRL/Mp (MRL, H-2k) recipient was performed in various combinations of donor and recipient mice with wild type (+/+), Fas-mutant (lpr) or FasL-mutant (gld) genotypes. The prolongation and spontaneous acceptance of the fully allogeneic grafts in recipients was not observed in either MRL-lpr recipients with B6+/+ livers or MRL+/+ recipients with B6-gld livers. Moreover, the serum alanine aminotransferase (ALT) levels and the degree of cell infiltration into hepatic allografts on day 7 after transplantation were inversely correlated with the recipient survival time (in days). The donor-specific cytotoxic T-lymphocyte (CTL) activities of the graft-infiltrating cells (GICs) from MRL-gld recipients with B6+/+ livers were much lower than those from MRL+/+ or -lpr recipients on days 5 and 10 after transplantation. However, the CTL activities of the GICs from MRL+/+ and -gld recipients predominantly disappeared by day 15 after transplantation. Furthermore, the anti-donor CTL activities induced in MRL+/+ recipients were ascribed to CD8+ cells, and were not mediated by Fas-FasL interactions. These results strongly suggest that the Fas/FasL system plays a critical role for recipient immunoregulation, enabling recipients in accepting hepatic allografts by deletion of the donor-specific T cells, but not for CTL/target cell interaction in MRL+/+ recipients.