Structure-function studies of S-antigen: use of proteases to reveal a dominant uveitogenic site

Retinal S-antigen induced experimental autoimmune uveitis (EAU) is a severe, predominantly T-cell mediated inflammatory disease of the uveal tract and retina of the eye. Pretreatment of LEW rats with the monoclonal antibody, MAbS2.4.C5, which defines an epitope in S-antigen, has been shown to effectively inhibit the subsequent induction of EAU with S-antigen. Using synthetic peptides and cyanogen bromide fragments of S-antigen we found the binding site of MAbS2.4.C5 to be located at the carboxy terminus of the molecule corresponding to amino acid positions 375 to 380. Limited Staphylococcus aureus V8 protease digestion yielded several polypeptide fragments including one large 43 kD fragment which retained antibody binding to a variety of both polyclonal and monoclonal antibodies which identify epitopes that span the length of the S-antigen. This treatment, however, completely destroys the MAbS2.4.C5 binding site and dramatically reduces uveitopathogenicity. Limited trypsin and papain digestion, on the other hand, had little effect on pathogenicity or on MAbS2.4.C5 binding to S-antigen or its peptide fragments. These results indicate that the carboxy-terminus of S-antigen plays a predominant role in the pathogenesis of EAU.

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.

The Waldeyer ring equivalent in the rat. A model for analysis of oronasopharyngeal immune responses

By means of serial sectioning of the head and neck a paired, rod shaped, parachoanic lymphoid organ was identified in Lewis rats. Histological, ultrastructural studies and FACS analysis showed this organ to be a lympho-epithelial organ with high endothelial venules (HEV) and a preponderance of B over T and T helper over T suppressor cells. Consequently this organ resembles the pharyngeal tonsil of man, and it is called the Waldeyer ring equivalent (WRE). The lymphatic drainage of this organ occurs predominantly to the deep, and to a lesser extent to the superficial cervical lymph nodes. Migration studies with 51Cr labeled cells show that the WRE lymphoid cells migrate into the lymphoid organs with HEV (peripheral lymph nodes. Peyer patches and WRE). In this respect they resemble peripheral lymph node cells more than cells from the Peyer patches. Thus the WRE lymphoid tissue in the rat is undoubtedly involved in local oronasopharyngeal immune surveillance and may also contribute to mucosal and systemic immune responses.

Prostaglandin E2 production by rat peritoneal macrophages: role of cellular and humoral factors in vivo in transfusion-associated immunosuppression

The transfusion of blood is associated with long-term immunosuppression, which has been postulated to influence immunosurveillance and cancer cell killing. The mononuclear phagocyte synthesises large quantities of PGE2, and PGE2 has been shown to inhibit the activity of a range of immunocompetent cell types. The role of mononuclear phagocyte PGE2 synthesis in transfusion-associated immunosuppression, and the elements of transfused blood which control this immunosuppression, were investigated using a transfused rat model. A significant increase in macrophage PGE2 synthesis was detected 7 days after transfusion with blood and serum. The storage of blood for 24 h increased the stimulatory activity of transfused blood. The effects of storage and serum on macrophage PGE2 synthesis were greater than effects due to genetic differences between blood donor and recipient, and the serum effects indicated that a major factor activating PGE2-mediated immunosuppression in transfused subjects may be humoral in nature.

A novel experimental model of giant cell myocarditis induced in rats by immunization with cardiac myosin fraction

It is suspected that autoimmune disease processes are involved in the pathogenesis of a part of giant cell myocarditis. However, evidence for autoimmunity has rarely been demonstrated in clinical investigations. In this study, we have demonstrated a new animal model of autoimmune myocarditis characterized by the appearance of multinucleated giant cells. Lewis rats were immunized twice with human cardiac myosin fraction in complete Freund's adjuvant. Cardiac myosin fraction was prepared from the ventricular muscle of human hearts. Three weeks after the first immunization, acute and severe myocarditis was elicited in all rats. This myocarditis was characterized by massive pericardial effusion, enlargement of the heart, and gray discoloration of the cardiac muscle. Microscopically, there was marked cellular infiltration consisting of mononuclear cells, neutrophils, fibroblasts, and a considerable number of multinucleated giant cells. Extensive myocardial necrosis was also present. The heart weights increased from the third week to the fourth week and then gradually decreased. The titer of anti-myosin antibodies began to elevate from the second week and remained high until the sixth week. In the sixth week, inflammation became smoldering and the multinucleated giant cells disappeared. These findings indicate that the cardiac myosin fraction contains myocarditogenic antigen and that giant cell myocarditis can be induced by autoimmune involvement. To our knowledge, this is the first report of experimental giant cell myocarditis, which is closely similar to human giant cell myocarditis in its histology and clinical course.

Suppression of hepatic allograft rejection in the rat by mitomycin C-treated donor splenocytes: analysis of the immune status

A single intraperitoneal injection of 3 x 10(6) donor splenocytes treated with mitomycin c (MMC) seven days before hepatic transplantation prolongs survival of hepatic allografts in the ACI (RT1a) to LEW (RT1l) rat combination. This effect is donor specific. An intravenous injection of the same dose of splenocytes treated with MMC seven days before transplantation also tends to prolong hepatic allograft survival. Furthermore, lymphocytotoxic antibody can be detected in rats 30 days after transplantation. Adoptive transfer of 5 x 10(7) splenocytes taken from long-term surviving hepatic allograft recipients pretreated with MMC-treated donor ACI splenocytes into irradiated (750 rads) LEW rats prolongs the survival of donor-type skin grafts, whereas third-party strain (BN) grafts are rejected. Similarly, prolonged survival of ACI cardiac allografts in irradiated (450 rads) LEW recipients is achieved following the transfer of spleen cells taken from longterm surviving hepatic allograft recipients pretreated with MMC-treated donor ACI splenocytes, whereas third-party (BN) cardiac allografts show rejection. These findings suggest the presence of donor-specific suppressor cells and indicate that a single injection of donor splenocytes treated with MMC to the recipient seven days before transplantation can induce specific suppression of rejection in a rat hepatic allograft model.

Cytotoxic T-cell precursors with low-level CD8 in the diabetes-prone Biobreeding rat: implications for generation of an autoimmune T-cell repertoire

Lymphocytes from diabetes-prone Biobreeding rats consistently fail to generate T-cell-mediated cytotoxicity under conditions where cytotoxic T lymphocyte activity is readily demonstrated in normal rats. The failure is associated with generalized T-cell lymphopenia and marked reduction in the frequency of CD8+ cells. The few remaining CD8+ cells are widely held to be natural killer cells rather than class I major histocompatibility complex-restricted T lymphocytes. In this report we show that a detectable percentage of CD8+ lymphocytes express the T-cell receptor for antigen, thus identifying them as part of the T-cell lineage. The failure of these CD8+ T-cell-receptor-positive T cells to lyse target cells that are susceptible to T-cell mediated cytotoxicity is associated with markedly reduced expression of cell-surface CD8. Targets expressing higher than normal levels of class I major histocompatibility complex target antigen could be lysed, suggesting that reduction in CD8 has decreased T-cell activity for target antigen. We discuss the derivation of T cells that express low levels of CD8 and the role they could play in generating autoimmune diabetes.

Population kinetics of peritoneal LPS-reactive B lymphocytes

The dynamic behaviour of isolated populations of peritoneal LPS-reactive (LPSr) B lymphocytes was studied upon transfer of peritoneal cells (PerC) from C57BL/6 LPS responder into C57BL/10ScCr LPS non-responder mice. We have followed the persistence and life-span of the transferred LPSr donor B cells in the spleen and peritoneal cavity of both intact and X-irradiated adult hosts after i.v. or i.p injection and neonatal 1-day-old recipients after i.v. transfer. We have found that lymphocyte life-spans can be influenced by local host environments, as the transferred PerC LPSr cells showed different kinetics according to their route of injection, organ localization, and age or state of the recipients. Thus, while in intact hosts most of the transferred peritoneal LPSr cells decayed with time, following transfer into X-irradiated recipients the same cells were able to expand and replenish the lymphoid tissues of the host. Moreover, upon transfer into intact hosts, the kinetic properties of peritoneal LPSr cells from adult mice differ from splenic LPSr cells of age-matched animals, but mimic those of spleen cells from young, 1-to 2-week-old donors. These findings may reflect the different phenotype composition of adult spleen cells (poor in Ly1 B cells) and peritoneal and neonatal spleen cells (both rich for Ly1 B cells), or may be the result of selective events leading to the peritoneal accumulation of cells with different population dynamics.

Identification of a cell surface 105 kd protein (Aic-2 antigen) which binds interleukin-3

A mouse interleukin-3 (IL-3)-binding molecule that is an essential constituent of the mouse IL-3 receptor complex was identified as a cell surface protein of Mr 105 kd. A rat monoclonal antibody, anti-Aic-2 IgM, recognized and immunoprecipitated a cell surface 105 kd protein (Aic-2 antigen). The antigen (Aic-2) and IL-3 receptor were co-down-regulated upon incubation of IL-3-dependent mouse IC2 cells with either anti-Aic-2 IgM or IL-3 at 37 degrees C, whereas anti-Aic-2 did not inhibit the binding of IL-3 to IC2 cells at 15 degrees C. The Aic-2 antigen and IL-3 receptor were co-distributed on various cell lines and cell types. IL-3 was shown to bind specifically to the Aic-2 antigen (Mr 105 kd) in the immunoprecipitated complex with anti-Aic-2. Chemically cross-linking of IL-3 to surface molecules of IC2 cells produced three types of complexes with Mr 95, 140, and 200-340 kd in SDS-PAGE, and pre-incubation with anti-Aic-2 IgM at 37 degrees C reduced the intensity of the three bands to the same degree. Moreover, anti-Aic-2 immunoprecipitated these three IL-3-cross-linked complexes, whereas the same monoclonal antibody recognized a single 105 kd molecule. Anti-Aic-2 IgM enhanced IL-3-dependent growth of IC2 cells though it did not promote proliferation of IC2 cells.

Serum antibody does not account for differences in the severity of chronic respiratory disease caused by Mycoplasma pulmonis in LEW and F344 rats

Chronic respiratory disease in rats, resulting from Mycoplasma pulmonis infection, is useful in the study of the immunological mechanisms in similar inflammatory diseases and provides a unique opportunity to study the interactions between systemic and mucosal immune systems in a naturally occurring infection. The present study examined the serum antibody responses to M. pulmonis in strains of rats which differ in disease progression and severity; LEW rats developed more severe disease than did F344 rats. Serum antibody responses were evaluated as to their levels, isotypes, and antigens recognized. Infected LEW rats produced greater or equal levels of the major classes of serum antibody to M. pulmonis than did infected F344 rats, suggesting that development of serum antibody responses alone does not resolve lesions and is not responsible for the difference in disease severity found in LEW and F344 rats. Although LEW rats produced higher responses in all subclasses of immunoglobulin G (IgG), the specific IgG response of LEW rats was composed predominately of IgG1 and IgG2a subclasses, while IgG2b was the major component of the IgG response in F344 rats. Finally, LEW rats responded more quickly to M. pulmonis antigens than did F344 rats, and there was no difference in the antigens eventually recognized by each strain, confirming previous work which suggested that LEW rats do not exhibit an unresponsiveness to a specific antigen(s) of M. pulmonis.

Glial cells as suppressor cells: characterization of the inhibitory function

Rat retinal glial cells (Müller cells) profoundly suppress antigen-driven activation, as well as the subsequent interleukin-2 (IL-2)-dependent expansion of autoimmune and conventional-immune syngeneic T-helper lymphocytes, through a contact-dependent mechanism. Characterization of this inhibitory function showed that some activation parameters of autoimmune T-helper lymphocytes specific to the retinal soluble antigen, responding to antigen presented on syngeneic antigen-presenting cells, were differentially affected by coculture with Müller cells. In contrast to endogenous IL-2 production, IL-2-receptor generation and proliferation, the production of interleukin-3 and of interferon-gamma were not inhibited. Inhibition of IL-2-supported proliferation of cells which had already generated the IL-2 receptor was markedly potentiated in the presence of the specific antigen, in a dose-dependent manner. The extent of inhibition was proportional to the number of Müller cells in the culture. The suppression appeared not to involve a major histocompatibility complex (MHC) Class II-related interaction and could act across allogeneic and even xenogeneic barriers. Inhibition affected normal lymphocytes, including primed T cells responding to antigen or to IL-2, unprimed spleen cells responding to the T-cell mitogen concanavalin A (Con-A) and, to a lesser extent, unprimed spleen cells responding to the B-cell mitogen bacterial lipopolysaccharide (LPS). Several permanently transformed cell lines of mouse, rat and human origin were not affected. These results may suggest participation of organ-resident cells in regulation of locally occurring immune processes.

Genetic resistance in experimental autoimmune encephalomyelitis. I. Analysis of the mechanism of LeR resistance using radiation chimeras

Experimental autoimmune encephalomyelitis (EAE) is a cell-mediated autoimmune disease of the central nervous system that has been extensively studied in the rat. The Lewis rat is highly susceptible to the induction of EAE, while the Lewis resistant (LeR) rat is known to be resistant. In this paper, we demonstrate that the LeR rat, which was derived from the Lewis strain by inbreeding of fully resistant animals, is histocompatible with the Lewis strain. Radiation chimeras, a tool for distinguishing between immunologic and nonimmunologic resistance mechanisms, were utilized to analyze the cellular mechanisms involved in genetic resistance to EAE. By transplanting bone marrow cells from LeR rats into irradiated Lewis recipients, Lewis rats were rendered resistant to EAE induction. Likewise, transplanting Lewis bone marrow cells into irradiated LeR recipients rendered LeR rats susceptible. Mixed lymphoid cell chimeras using bone marrow, spleen, and thymus cells in Lewis recipient rats revealed individual lymphoid cell types and cell interactions that significantly affected the incidence and severity of EAE. Our results suggest that LeR resistance is mediated by hematopoietic/immune cells, and that cells located in the spleen appear to play a critical role in the resistance/susceptibility to EAE induction. Depletion of splenic adherent cells did not change the patterns of EAE resistance. In vivo cell mixing studies suggested the presence of a suppressor cell population in the LeR spleen preparations which exerted an inhibitory effect on Lewis autoimmune responses. Thus, the mechanism of LeR resistance appears to be different from that in other EAE-resistant animals.

Clonotypic heterogeneity of Lewis rat T cells specific for the encephalitogenic 68-86 region of myelin basic protein

Experimental autoimmune encephalomyelitis was induced in a Lewis rat by sensitization with synthetic peptide GP68-86, representing the 68-86 sequence of guinea pig myelin basic protein (GPMBP). To delineate T cell determinants of GP68-86, lymph node cells from this rat were activated in culture with GP68-86 and were fused with cells of the mouse thymoma BW5147. The resultant hybrids were cloned by limiting dilution and screened for GP68-86-evoked secretion of IL2 in the presence of rat splenocytes. Twelve T cell hybrids derived in this manner were tested for reactivity to different heterologous species of MBP as well as to substituted or truncated analogs of GP68-86. The hybrids generally exhibited potent reactivity to GPMBP but differed markedly in their reactivity to autologous rat MBP (RMBP). A few exceptional hybrids exhibited crossreactivity with peptides in which native serine75 or serine80 residues of GPMBP were substituted with either alanine75 (A75) or proline80 (P80) residues. These cross-reactive hybrids also possessed high levels of anti-RMBP reactivity. The remaining hybrids were unresponsive to the A75 and P80 substituted peptides and, with one exception, had relatively low levels of anti-RMBP reactivity. Unique reactivity patterns were also revealed by hybrid responses to peptides having modified C-terminal 84-86 residues. In summary, the contrasting fine specificities of different hybrids indicated that several distinct clones of T cells mediate the immune response of Lewis rats against the 68-86 region of GPMBP. Furthermore, heterogeneity in the hybrid response to "self" RMBP may reflect substantial differences in encephalitogenic potency of the T cell clones from which these hybrids were derived.

Monocyte/macrophage procoagulant activity as a measure of immune responsiveness in Lewis and brown Norway inbred rats. Discordance with lymphocyte proliferative assays

In vitro lymphocyte proliferative assays were performed using Lewis (Lew) and Brown Norway (BN) rats, and compared to induction of monocyte/macrophage procoagulant activity (PCA) in a mixed lymphocyte culture and by endotoxin (LPS) (E. Coli 0111:B4). Splenic mononuclear cells from Lew rats had significantly greater mitogen-induced proliferation to concanavalin A (P = .002) and phytohemagglutinin (P = 0.007). The Lew cells also showed greater allogeneically induced proliferation by BN cells in a one-way MLC in comparison to the reciprocal BN proliferative response (P less than 0.04). PCA induction in peripheral blood mononuclear cells (PBM) by allogeneic stimulation in MLC or total content PCA by LPS did not vary significantly between the 2 strains (P greater than 0.5). Induction of PCA by LPS was rapid, with a moderate rise over basal activity at 3 hr and maximal activity at 6 hr. Two-way allogeneic induction of PCA in PBM from BN and Lew rats resulted in PCA elevation by 3 hr, which became maximal at 18 hr. One-way MLC with Lew or BN cells as responders resulted in moderate increases in PCA by 3-6 hr, with equivalent maximal activities recorded at 18 hr. Viable PCA accounted for 26-32% of total content PCA in both Lew and BN rats. Maximal allogeneic PCA induction by MLC was 14-18% of PCA induced by LPS and required a longer incubation for its expression. Our results indicate that in vitro PCA expression by Lew and BN PBM following allogeneic or endotoxin stimulation shows little interstrain variability in comparison to lymphocyte proliferative responses. Thus PCA appears to more closely reflect the observed in vivo responses of these strains to allogeneic challenge.

Immunotherapy of experimental autoimmune encephalomyelitis (EAE): differential effect of anti-IL-2 receptor antibody therapy on actively induced and T-line mediated EAE of the Lewis rat

Treatment of Lewis rats with monoclonal anti-interleukin-2 receptor (IL-2 R) antibody ART-18 is highly efficient in protecting the recipients from T-line transferred experimental autoimmune encephalomyelitis (tEAE) in vivo. In contrast, ART-18 did not affect the development of EAE actively induced (aEAE) by immunization with myelin basic protein (MBP) in complete Freund's adjuvant (CFA). ART-18 caused a slight delay in the development of aEAE only in combination with a subtherapeutic dose of cyclosporine A (Cy-A), but failed to influence duration or severity of clinical signs. The discrepancy in therapeutic efficiency of ART-18 in tEAE and aEAE could be due to a different intensity of IL-2 R-expression on in vitro- and in vivo-activated MBP-specific T cells. Our results therefore caution against a general therapeutic application of anti IL-2 R-directed therapy in all manifestations of T-cell-mediated autoimmunity.

Vaccination against experimental autoimmune encephalomyelitis using a subencephalitogenic dose of autoimmune effector T cells. (2). Induction of a protective anti-idiotypic response

We previously reported that a subencephalitogenic dose (10(4) of activated anti-BP Z1a T cells rendered Lewis rats significantly resistant to EAE induced either actively or adoptively. This resistance was specific to EAE and persisted for over 4 months. The experiments reported in this paper were done to investigate the mechanisms of this resistance. We found that the state of vaccination was marked by a decrease in the in vitro proliferation and in vivo DTH responses to BP. Resistance could be transferred to recipient rats with the thymus or spleen cells of donor vaccinated rats. Vaccination led to the appearance of proliferative and DTH responses that were specifically directed to the Z1a T cells. The kinetics and compartmentalization of this anti-idiotypic responsiveness was studied by vaccinating rats in the hind footpads and monitoring the proliferative reactivity of the draining popliteal lymph node (PLN) and distal cervical lymph node (CLN) cells at various times. We found that the anti-idiotypic reactivity was confined to the PLN on days 5-6 and thereafter became systemic. Excision of the PLN on day 6, but not on days 3 or 11, robbed the rats of their acquired resistance to EAE. In contrast, the PLN cells of the vaccinated rats transferred resistance to naive donors. Thus, the lymphoid population containing cell-mediated anti-idiotypic responsiveness served as a vehicle of resistance. These results suggest that anti-idiotypic T-cell immunity to autoimmune effector T cells is involved in the resistance to EAE induced by T-cell vaccination.

Lymphocyte proliferative response to glial cells in SJL/J mice immunized with rat whole spinal cord and rat myelin basic protein

Lymph node cells (LNC) from SJL/J mice immunized with either rat whole spinal cord (WSC) homogenate or rat myelin basic protein (MBP) in the presence of complete Freund's adjuvant were assayed for their in vitro proliferative response to MBP and whole or sonicated purified oligodendrocytes (OD), and astrocytes. WSC-immunized mice displayed a strong and persistent response to both syngeneic and rat OD, that disappeared after sonication (suggesting a preferential recognition of surface OD antigen(s], and a much weaker response to rat MBP. LNC from MBP-immunized mice showed a small response to MBP, but no response to OD, indicating that OD are not able to present their endogenous MBP to lymphocytes. Conversely, rat astrocytes (whole or sonicated), isolated from cultures initially comprising OD, could trigger the proliferative response of MBP-sensitized LNC, suggesting that astrocytes may act as antigen-presenting cells for OD products.

Lymphocyte vaccination against experimental autoimmune encephalomyelitis: evaluation of vaccination protocols

Repeated vaccination with encephalitogenic but not other T cell lines could effect marked resistance to 'active' experimental autoimmune encephalomyelitis (EAE) induced by injection of GP-BP in adjuvant. Partial resistance to active EAE was observed in rats recovered from 'passive' line-mediated EAE and in rats vaccinated with T cells attenuated by irradiation or ganglioside treatment. However, no resistance was observed in animals given low doses of activated encephalitogenic T cells. Treatment with hydrostatic pressure alone was found to be ineffective as a means of attenuation, and vaccination with pressure-treated encephalitogenic T cells actually induced mild signs of EAE. However, vaccination with cells that were first pressure treated and then irradiated prevented both clinical and histologic signs of active EAE. In contrast, protection against passive EAE appeared to be clonotypic. Lymphocyte vaccination induced delayed type hypersensitivity (DTH) reactions against autologous T cells, mostly to shared antigens, demonstrating the immunogenicity of multiple antigens on the vaccinating cells.

Induction of Ia molecules on brain endothelium is related to susceptibility to experimental allergic encephalomyelitis

We have examined the responses of brain endothelium from different rat strains to interferon-gamma (IFN-gamma) which induces expression of MHC class II molecules. There is a marked difference between the strains in the sensitivity of their endothelium to MHC induction. LEW and DA rats, which are susceptible to experimental allergic encephalomyelitis (EAE) can be induced to express higher levels of class II molecules than EAE-resistant strains. In both the EAE-susceptible and -resistant strains, RT-1B locus-encoded molecules occur at higher surface densities than RT-1D locus molecules. These findings support the theory that genes controlling the induction of MHC expression affect disease susceptibility.

Immunomagnetic T-lymphocyte depletion (ITLD) of rat bone marrow using OX-19 monoclonal antibody

Graft versus host disease (GVHD) may be abrogated and host survival prolonged by in vitro depletion of T lymphocytes from bone marrow (BM) prior to allotransplantation. Using a mouse anti-rat pan T-lymphocyte monoclonal antibody (OX19) bound to monosized, magnetic, polymer beads, T lymphocytes were removed in vitro from normal bone marrow. The removal of the T lymphocytes was confirmed by flow cytometry. Injection of the T-lymphocyte-depleted bone marrow into fully allogeneic rats prevents the induction of GVHD and prolongs host survival.

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)).

The mechanism of discordant xenograft rejection

The mechanism of discordant xenograft rejection using the guinea pig-to-rat heart graft model was studied. In this model, we found that (A) Rejection occurred rapidly, in 17.5 +/- 8.3 min (mean +/- SD) (n = 8). (B) The graft survived longer when the recipient rat was pretreated with cobra venom facter (CVF). (C) Complement hemolytic titers in serum showed significant reduction of C3 in rejection without consumption of C4 and C2, suggesting complement activation through the alternative pathway. (D) No natural antibodies were detected in this combination. Complement-dependent cytotoxicity (CDC) titer, and hemagglutination (HA) titer were lower than x1. (E) Histological examination of the rejected heart xenograft revealed a large area of myocytolysis without interstitial cellular infiltration. (F) In vitro experiments showed that rat complement attacked guinea pig erythrocytes (Egp) via the alternative pathway. These findings indicate that rejection in this discordant xenograft model of guinea pig-to-rat was caused by primary activation of complement via the alternative pathway.

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.