Role for interferon-gamma in rat strains with different susceptibility to experimental autoimmune myasthenia gravis.

Experimental autoimmune myasthenia gravis (EAMG) is caused by autoantibodies against the nicotinic acetylcholine receptor (AChR) at the neuromuscular postsynaptic membrane and represents an animal model of myasthenia gravis in human. Recent studies highlighted the roles of TH1 cytokines (IFN-gamma, IL-12), rather than TH2 cytokines (IL-4), in the pathogenesis of EAMG by using homozygous (-/-) knockout mice with an EAMG-susceptible genetic background. To further evaluate a role for IFN-gamma, we injected recombinant rat IFN-gamma (rrIFN-gamma) at the time of immunization with AChR in complete Freund's adjuvant to EAMG-susceptible Lewis rats and EAMG-resistant Wistar Furth (WF) rats. RrIFN-gamma enhanced Lewis rat EAMG. The exacerbated muscular weakness was associated with higher levels of anti-AChR IgG and enhanced TNF-alpha responses. Anti-AChR IgG antibody levels were augmented to a similar extent as in Lewis rats, however, the identical immunization and IFN-gamma injection induced only mild and transient EAMG in WF rats due to the default TH3 phenotype development and inherent low TH1 responses. We conclude that IFN-gamma plays a major role in the pathogenesis of EAMG in the Lewis rat, but fails to break disease resistance in the WF rat.

Comparative studies of specific acquired systemic tolerance induced by intrathymic inoculation of a single synthetic Wistar-Furth (RT1U) allo-MHC class I (RT1.AU) peptide or WAG (RT1U)-derived class I peptide.

BACKGROUND: Because T cell receptor-MHC class I/self-peptide interactions regulate T-cell development, the presence of MHC allopeptides in the thymus may influence T-cell tolerance to alloantigens. This hypothesis is supported by our most recent finding that intrathymic (IT) inoculation of nonimmunogenic synthetic peptides derived from "WAG" RT1.A induces tolerance to cardiac allografts in the Wistar-Furth (WF)-to-ACI model. To evaluate whether in vivo immunogenicity of MHC peptides is relevant to tolerance induction and to examine the effect of peptide specificity, we compared the effects on graft survival of well-defined, strain-specific immunogenic WF MHC class I peptides (RT1.AU) with closely related but non-strain-specific class I peptides derived from WAG (RT1U). METHODS: In vivo immunization of seven MHC class I peptides synthesized from RT1.AU sequences showed that two (u-5 and u-7) were immunogenic, whereas five others were not immunogenic in ACI recipients. We then examined the effects on cardiac allograft survival in the WF-to-ACI model of the two immunogenic RT1.AU peptides (u-5 and u-7) and three immunogenic WAG-derived peptides (peptides 1, 2, and 5). RESULTS: A combination of equal amounts (150 microg or 300 microg) of u-5 or u-7 each with 0.5 ml of antilymphocyte serum (ALS) on day -7 led to 60% and 100% permanent graft survival (>150 days), respectively. IT injection of the individual peptides on day -7 showed that only 300 microg of u-5 significantly prolonged graft survival to a median survival time of 17.3 days from 10.5 days in naive recipients. IT injection of 150, 300, and 600 microg of u-5 combined with 0.5 ml of ALS on day -7 led to permanent graft survival (> 150 days) in four of six, nine of nine, and six of six ACI recipients, respectively, compared with a median survival time of 15.4 days in ALS alone-treated controls. In contrast, similar treatments with peptide u-7 with or without 0.5 ml of ALS did not prolong graft survival, thus demonstrating that peptide u-5 alone mediates the observed effects on graft prolongation. A total of 300 microg of u-5 injected IT combined with ALS led to acute rejection of third-party (Lewis) grafts. Intravenous injection of 300 microg of u-5 with ALS also did not prolong WF graft survival in ACI recipients. The long-term unresponsive ACI recipients accepted permanently donor-type (WF) but not third-party (Lewis) second-set cardiac and islet allografts. Similarly, we showed that although IT injection of 600 and 1200 microg of a mixture of immunogenic WAG-derived peptides 1, 2, and 5 combined with 0.5 ml of ALS on day -7 led to permanent WF graft survival in ACI, only IT injection of 300 microg of peptide 2 combined with ALS led to permanent graft survival (>150 days) in four of five animals. To define the underlying mechanisms of tolerance, we examined in vitro the mixed lymphocyte reaction (MLR), cell-mediated lymphocytotoxicity, and cytokine profile of unresponsive recipients. Although the results showed nonspecific T-cell suppression in the MLR at 25 days after transplantation, which correlated with the persistence of ALS immunosuppression, long-term unresponsive animals showed normal MLR to donor and third-party antigens. In contrast, the donor-specific reactive cytotoxic T lymphocytes remained suppressed in short-term and long-term unresponsive rats. CONCLUSION: Of interest is our finding that IT injection of a short segment of WAG-derived MHC class I peptide induces active acquired tolerance similar to results obtained with the use of pure WF-derived peptide u-5 in the WF-to-ACI rat combination. It is noteworthy that we could not confirm the T helper (Th)1/Th2 paradigm in this model by initial cytokine analysis. Whether induction of tolerance by IT injection of allo-MHC peptides will have clinical usefulness must await results of similar studies in large animals. However, of major interest is the finding that a short segment of RT1.AU represents the tolerogenic

Quantitative analyses comparing all major spleen cell phenotypes in BB and normal rats: autoimmune imbalance and double negative T cells associated with resistant, prone and diabetic animals.

The BB rat is a model of spontaneous autoimmune diabetes. To characterize quantitatively all known immune cell subsets involved in disease pathogenesis, FACS analysis of spleen cells was performed in diabetes-prone (DP) and acutely diabetic (D) BB rats and compared with diabetes-resistant (DR) BB and normal Wistar-Furth (WF) strains. We observed increased percentages of splenic NK cells in DP and D animals compared with DR rats using an NK-specific monoclonal antibody. We found increased proportions of splenic macrophages in the T-lymphopenic DP and D rats and low macrophage contents in DR spleens compared with WF spleens. We observed that percentages of the CD4-CD8- T cell receptor alpha/beta+ (double-negative) T cell subset were strikingly increased in the lymphopenic DP and D animals, compared with DR animals. We observed increased percentages of activated splenic CD5+ T cells expressing the IL-2 receptor and MHC class II antigen in DP and D rats compared with DR animals. Our studies suggest that (a) splenic NK cells and macrophages quantitatively appear to be involved in the pathogenesis of diabetes; (b) double-negative T cells escape from the T cell depletion process; (c) a marked increase of activated splenic T cells suggests diabetes is associated with general T cell activation processes; and (d) an altered balance among the different immune cell subsets may in part explain the pathogenesis of diabetes, since marked relative changes are observed when comparing the DR strain to the DP strain in both the prediabetic and diabetic stages.

Cyclosporin A, FK506, rapamycin: the use of a quantitative analytic tool to discriminate immunosuppressive drug interactions.

Potent immunosuppressive agents display toxic complications at full therapeutic doses: cyclosporin A (CsA) produces pleiotropic mesenchymal effects with prominent vasculopathy, whereas FK506 displays severe neurotoxicity associated with a similar range of mesenchymal and possibly vasculitic reactions. The concept of drug synergy seeks to exploit combinations of agents that promote each other's immunosuppressive effects. This article presents a quantitative method to assess synergy in vitro and in vivo--the median-effect analysis. Application of this method revealed synergistic interactions of CsA with steroids, an additive effect with azathioprine, and antagonistic effects with FK506 and enisoprost. Clearly, a synergistic therapeutic combination can be clinically useful only if it is not associated with a similar potentiation of toxic complications. Clinical practice has documented the synergistic relation of CsA plus steroids and the antagonistic relation of CsA with FK506 or enisoprost. Clinical trials of rapamycin, which displays extremely potent synergistic effects with CsA both in vitro with human and in vivo with animal immune responses, may afford important new insights for clinical immunosuppression.

Characterization of RT6-bearing rat lymphocytes. II. Developmental relationships of RT6- and RT6+ T cells.

The derivation of RT6+ T cells from postthymic RT6- T cells in weanling rats was formally demonstrated by the intravenous transfer ("parking") of highly purified populations of RT6- lymph node T cells into thymectomized, irradiated, and bone-marrow-reconstituted (TXBM) RT6 and RT7 alloantigen-disparate recipients. Parallel experiments in irradiated and bone-marrow-reconstituted rats, and in rats whose RT6+ T cells had been depleted by injection of DS4.23 anti-RT6.1 mAb, suggested that the transit time between the pre-RT6+ and the RT6+ T-cell compartments approximated 4-5 days. A more precise estimate of the transit time was made by linear regression analysis of the generation of RT6+ T cells in rats that were treated with DS4.23 mAb at timed intervals after thymectomy. This study indicated that 50% of the pre-RT6+ T cells differentiated into RT6+ cells within 4 days, 75% within 8 days, and more than 90% within 16 days. Despite the apparent absence of pre-RT6- T cells 3 weeks after thymectomy, numerous RT6- T cells persisted for at least 10 weeks in thymectomized rats, even after treatment with DS4.23 mAb. Moreover, these RT6+ T cells failed to generate RT6+ T cells after transfer into adoptive hosts. Quantitative and phenotypic analyses indicated that this population of "true" RT6- T cells: (1) constitutes approximately 50% of the total RT6- T cells normally found in control rats; (2) contains CD4+ and CD8+ subsets; (3) expresses both the CD5 pan-T-cell antigen (which is absent from NK cells) and the R73 alpha/beta TCR constant-region determinant; and (4) lacks sIgM. Hence, the present results indicate that the "true" RT6- and the RT6+ T-cell subsets have stable antigenic phenotypes and represent developmentally discrete populations of postthymic cells in normal rats. This is supported by associated phenotypic and functional studies that suggest that the "true" RT6- T-cell subset contains antigenically naive and/or autoreactive clonotypes, whereas the RT6+ T-cell subset contains memory and/or regulatory cells. It remains to be determined whether the "true" RT6- and the RT6+ subsets represent separate lineages of T cells or a single lineage at different stages of activation or maturation.

Properties of B cells and Thy-1-antigen-expressing cells infiltrating rat renal allografts.

We have examined (1) the frequency of B cells secreting antibodies against donor major histocompatibility complex (MHC) antigens and (2) the properties of Thy-1-antigen-expressing leukocytes in rats rejecting renal allografts. Our results show that B cells secreting antibodies are present in the inflammatory cell population at the frequency of 1:850. Among them only 1 out of 2-150 is engaged in production of antibodies directed to the graft MHC antigens, depending on the method of assay. This suggests that despite the observed significant production of nonspecific immunoglobulin in situ, only a minority of the B-cell population is specifically committed to the graft MHC antigens. This finding is concordant with the described previously low frequencies of the T cells specifically directed toward the graft MHC antigen. The role of the "immunologically noncommitted" cells in graft rejection is unknown. We have found that a substantial part (up to 60%) of inflammatory cells invading a rat kidney allograft express the Thy-1 antigen. This suggests that they might be immature (progenitor?) cells and, therefore, unable to respond to the graft antigens. Progenitor-like properties of these cells have been confirmed by their ability to reconstitute lethally irradiated syngeneic rat. Finally, these immature cells are of lymphoid, not of myeloid, linkage, because they do not proliferate in the presence of GM-CSF.

Unaltered class II histocompatibility antigens and pathogenesis of IDDM in BB rats.

The BB rat spontaneously develops insulin-dependent diabetes mellitus (IDDM) as an autoimmune abnormality involving the class II molecules of the major histocompatibility complex (MHC). The rat MHC (RT1 complex) encodes two class II loci, RT1.B and RT1.D. The possibility that variant or unique class II MHC molecules may be associated with IDDM susceptibility was directly examined by determining the nucleotide sequences of class II mRNAs and/or cDNAs from the diabetes-prone (DP) BB rat, the diabetes-resistant (DR) BB rat, the normal histocompatible Wistar-Furth (WF) rat, and the Lewis rat. Sequence analysis indicates that the beta-chains of the RT1.B and RT1.D molecules of the u haplotype from DP-BB, DR-BB, and WF rats are identical but that they are different from other rat alleles and published mouse class II sequences. At the nucleotide level, the NH2-terminal domain of RT1.D beta of the BB and WF rats differs by a single silent nucleotide substitution. Comparisons with the sequences of the Lewis rat indicate hypervariable allelic differences and that the u and I haplotypes are remarkably similar. These findings establish that the class II molecules of the DP-BB rat are not variant or unique and that unaltered class II molecules of the u haplotype support the autoimmune response in the BB rat.

Experimental autoimmune encephalomyelitis in a low-susceptible rat strain.

The susceptibility to the induction of experimental autoimmune encephalomyelitis has been investigated in the previously little known Wistar/Furth rat stain. These rats have a low sensitivity, similar to that of the Fischer and PVG strains previously studied at our laboratory. However, some differences appear in the histological response of the three strains when a treatment with pertussis or cyclophosphamide is performed prior to the immunization, suggesting that different temporal patterns exist in the development of histological signs, according to the genetic background. The infiltrating cells may have different functions in rats of different genotypes.

Induction of a suppressive serum factor, prevention of sensitization, and prolongation of kidney graft survival in rats by transfusion with antibody-coated blood cells.

Transfusion with antibody-coated allogeneic blood cells suppresses the cytotoxic antidonor antibody response in a strongly incompatible rat combination (BN----LEW). Cell coating with homologous recipient antidonor antiserum, rat monoclonal antibodies against MHC class I donor antigens, or rabbit antirat lymphocyte serum all were effective. The suppression was not abrogated by repeated booster transfusions with untreated donor blood. Moreover, the suppression extended to antibody-uncoated antigens present on the same donor cell. Not only the antibody response but also the Graft-versus-host reaction against donor antigens was suppressed. The serum of pretreated animals contained suppressive activity. It suppressed the cytotoxic antibody response as well as the cellular immune response (GVH) when transferred into syngeneic recipients. A weaker suppression of antibody response was obtained by transferring spleen cells of pretreated animals into syngeneic recipients. The transfer data suggest that broadly reactive serum factor(s) were mainly responsible for the suppressive effect. Transfusion with LEW-anti-BN-coated donor cells before transplantation induced markedly prolonged kidney graft survival in the BN----LEW combination without additional immunosuppression (untreated controls: 8.4 +/- 0.4, pretreated recipients: 124 +/- 36 days, P less than 10(-4)).

Specificity of the T cell immune response to acetylcholine receptor in experimental autoimmune myasthenia gravis. Response to subunits and synthetic peptides.

Myasthenia gravis (MG) and its animal model, experimental autoimmune MG (EAMG), are T cell-dependent diseases mediated by antibodies against acetylcholine receptor (AChR) on skeletal muscle. Most of the antibodies are directed toward conformation-dependent epitopes on the AChR, whereas T cells recognize denatured AChR. In search of T cell epitopes in EAMG, we tested 24 synthetic peptides covering 62% of the alpha-subunit sequence of Torpedo californica electric organ AChR in the T cell proliferation assay with lymph node cells from rats immunized with AChR. In Lewis rats, 2 of these peptides, [Tyr 100]alpha 100-116 and [Gly 89, Tyr 90]alpha 73-90, strongly stimulated T cells and, of these, [Tyr 100]alpha 100-116 was much more potent; 4 other peptides were weakly mitogenic and 18 were ineffective. None of the 24 synthetic peptides alone stimulated anti-AChR production and, when added to cultures along with AChR, [Tyr 100]alpha 100-116 and [Gly 89, Tyr 90]alpha 73-90 suppressed antibody production. Of twelve cloned T cell lines specific to AChR, 4 responded to [Tyr 100]alpha 100-116, indicating the importance of the epitope in alpha 101-116 in Lewis rats. In three other strains of rats whose responses to AChR and its subunits were similar to those in the Lewis rat, neither [Tyr 100]alpha 100-116 nor [Gly 89, Tyr 90]alpha 73-90 was stimulatory. Instead, completely different sets of peptides stimulated their T cells. When peptides were used as immunogens, each strain (except Lewis rats) responded only to the peptides that stimulated AChR-immune T cells from the same strain. Genetically restricted T cell recognition of AChR peptides in rats suggests that T cells from MG patients with different major histocompatibility haplotypes may recognize different AChR peptides.

Impact of class II major histocompatibility complex antigen expression on the immunogenic potential of isolated rat vascular endothelial cells.

We have investigated the immunogenic potential of rat heart vascular endothelial cells by their ability to induce an accelerated rejection of a relevant heart allograft, and related the immunogenic potential to the expression of class II major histocompatibility complex (MHC) antigens on the endothelial cell surface. Only 12% of freshly isolated rat vascular endothelial cells express class II antigens in serum-free medium, and the level of expression is low as judged by immunoperoxidase staining and/or the ability of endothelial cells to bind staphylococci to the cell surface after treatment with monoclonal antibodies to the class II molecule. On the other hand, 99% of the endothelial cells under the same conditions express class I, and the level of expression is high. The class II antigen expression of vascular endothelial cells can be upregulated to more than 98% by recombinant gamma-interferon in vitro--and, concomitantly, the level of expression becomes high, even on the cell surface. Treatment with gamma-interferon did not substantially alter the level of class I expression. The endothelial cells expressing class II antigens weakly, are also weakly immunogenic in vivo: 10(7) endothelial cells are required to reduce the graft survival by 50% of that of the unprimed host. On the contrary, the endothelial cells of the same lineage induced to express class II antigens by gamma-interferon in vitro are highly immunogenic in vivo, as immunogenic as freshly-isolated spleen dendritic cells: only 10(4) endothelial cells are required to induce a 50% reduction of graft survival. These observations demonstrate for the first time that rat vascular endothelial cells are immunogenic in a primary transplantation response in vivo--and, moreover, that the immunogenic capacity of the endothelial cells is directly proportional to the extent of class II MHC antigen expression on the cell surface.

Immunogenicity and tolerogenicity of a major house dust mite allergen, Der p I from Dermatophagoides pteronyssinus, in mice and rats.

Primary immunization of different inbred strains of mice with the house dust mite allergen Der p I (from Dermatophagoides pteronyssinus) adsorbed to adjuvant revealed differences in IgE but not IgG responses. Thus, the CBA and C57 Black strains were shown to be high IgE responders in that persistent IgE was induced which lasted for several months. In contrast, the C3H, AKR and Balb/c strains were judged to be poor responders. Subsequent experiments showed that such responses were adjuvant-independent, refractory to irradiation (850 rad) and that they could be adoptively transferred using immune spleen cells in a dose-dependent manner. At sub-optimal doses, adoptively transferred IgE responses were initiated by either intraperitoneal or intranasal challenge of recipients with allergen in the absence of adjuvant. Allergen-specific IgE in rats was also shown to be strain-dependent, with Brown Norway rats, in contrast to Wistar Furth (WF) and Lou/M rats, being the highest responder strain studied. Repeated intranasal administration of soluble allergen induced IgE tolerance in rats but not mice. However, tolerance was restricted to the low IgE responder phenotype strain, WF.

Characterization of IgE and IgG antibody responses to Dermatophagoides farinae in rats.

Rats (Brown Norway/Wistar Fu) that were pretreated or not pretreated with cyclophosphamide were immunized with varying amounts of Dermatophagoides farinae allergen extract with alum as adjuvant. Sera were analysed by RAST and by crossed radioimmunoelectrophoresis (CRIE). The highest IgE antibody responses were recorded in animals pretreated with cyclophosphamide that had received low immunizing doses of antigen. The IgE antibody pattern in CRIE was, however, not influenced by the dose of antigen or by cyclophosphamide pretreatment. The IgG pattern in CRIE closely resembled the IgE pattern, demonstrating a similar specificity of the antibody responses of the two isotypes. This indicates non-class specific control of the specificity of antibody responses.