Evidence that the T cell repertoire of normal rats contains cells with the potential to cause diabetes. Characterization of the CD4+ T cell subset that inhibits this autoimmune potential

Type 1 diabetes: the facts fit a deficient inhibitory signal given by MHC class II

This paper presents a hypothesis regarding the aetiology of Type 1 (autoimmune) diabetes, which suggests that autoimmunity is normally prevented by an inhibitory or negative signal delivered by MHC molecules, and that in Type 1 diabetes it is the inability of beta cells to deliver sufficient negative signal from MHC Class II that drives the underlying autoimmune process. Based on a broad survey of the diabetes literature, a list of clinical, pathological, experimental and epidemiological 'facts' about Type 1 diabetes is presented which are considered to be widely accepted as proven. The new theory is then compared to other recent theories on the aetiology of diabetes with regard to its ability to explain these accepted 'facts'.

Dominant regulation: a common mechanism of monoclonal antibody induced tolerance?

Transplantation tolerance can be induced by a range of agents that block T cell/antigen-presenting cell (APC) interactions known to be important for initiation of the adaptive immune response. Tolerance so induced has been shown to have a regulatory phenotype dependent on CD4+ cells. This was first observed with nonlytic anti-CD4 antibodies, and was recently demonstrated following other therapeutic approaches. Dominant tolerance also plays a role in natural regulation of the immune response, functioning to prevent autoaggressive cells mediating self-destruction. The mechanism by which dominant tolerance is established and maintained remains unclear, and the reported characteristics of regulatory cells in different experimental models vary widely. Here we review the evidence for potential mechanisms involved and propose that there is a common pathway by which dominant tolerance is mediated.

Cutting Edge: Linked Suppression of Skin Graft Rejection Can Operate Through Indirect Recognition

Adult mice can be rendered immunologically tolerant of allogeneic tissues if transplanted under cover of mAbs to CD4 and CD8. Tolerance generated in this manner is characterized by the presence of regulatory CD4+ T cells that can recruit naive T cells to become tolerant also through “infectious tolerance.” Regulatory CD4+ T cells can also suppress rejection of third party transplant Ags provided they are expressed on the same graft as the tolerated Ags. This process of linked suppression can act across whole MHC barriers and represents a powerful mechanism with therapeutic potential. Tolerance can also be induced to reprocessed minor transplantation Ags presented through host APCs (indirect recognition). We here demonstrate that linked suppression can also be induced through the indirect pathway. This finding may be important in the development of transplantation tolerance in the clinic.

Thymus-dependent monoclonal antibody-induced protection from transferred diabetes

It is well established that long-term protection from insulin-dependent diabetes mellitus (IDDM) can be afforded to non-obese diabetic (NOD) mice by a short course of non-depleting (nd) anti-CD4 monoclonal antibodies (mAb). Since it is increasingly apparent that the CD8+ T cell plays a prominent role in the development of IDDM, we have investigated the effect of an anti-CD8 mAb (YTS 105) of the same isotype in both spontaneous and induced IDDM in NOD mice. Treatment with YTS 105 for 3 weeks was able to prevent the transfer of IDDM for a long period, and also substantially reduced spontaneous IDDM in female NOD mice. The role of the thymus in tolerance induction by these antibodies was studied. In the adult transfer model, thymectomized NOD mice, unlike their euthymic counterparts, were not protected long-term by treatment with YTS 105, and began to become overtly diabetic shortly after treatment. This was also true when the nd anti-CD4 mAb was used. Protection from spontaneous disease was not affected in the same way by thymectomy. The reasons for the observed effect of the thymus in the transfer model, and the differences between the two models that may explain the contrasting results are discussed.

Control of immune pathology by regulatory T cells

There is now compelling evidence that immune responses for both foreign and self antigens are downregulated by T cells that are specialised for this function; these are known as regulatory T (T reg) cells. This review describes progress in the characterisation of the T reg cells that mediate both mucosal tolerance and tolerance to self antigens. The recent work on the antigen specificity, generation and mode of action of T reg cells is also reviewed.

Regulatory CD4(+) T cells expressing endogenous T cell receptor chains protect myelin basic protein-specific transgenic mice from spontaneous autoimmune encephalomyelitis

The development of T cell-mediated autoimmune diseases hinges on the balance between effector and regulatory mechanisms. Using two transgenic mouse lines expressing identical myelin basic protein (MBP)-specific T cell receptor (TCR) genes, we have previously shown that mice bearing exclusively MBP-specific T cells (designated T/R-) spontaneously develop experimental autoimmune encephalomyelitis (EAE), whereas mice bearing MBP-specific T cells as well as other lymphocytes (designated T/R+) did not. Here we demonstrate that T/R- mice can be protected from EAE by the early transfer of total splenocytes or purified CD4(+) T cells from normal donors. Moreover, whereas T/R+ mice crossed with B cell-deficient, gamma/delta T cell-deficient, or major histocompatibility complex class I-deficient mice did not develop EAE spontaneously, T/R+ mice crossed with TCR-alpha and -beta knockout mice developed EAE with the same incidence and severity as T/R- mice. In addition, MBP-specific transgenic mice that lack only endogenous TCR-alpha chains developed EAE with high incidence but reduced severity. Surprisingly, two-thirds of MBP-specific transgenic mice lacking only endogenous TCR-beta chains also developed EAE, suggesting that in T/R+ mice, cells with high protective activity escape TCR-beta chain allelic exclusion. Our study identifies CD4(+) T cells bearing endogenous alpha and beta TCR chains as the lymphocytes that prevent spontaneous EAE in T/R+ mice.

CD4(+) T cells prevent spontaneous experimental autoimmune encephalomyelitis in anti-myelin basic protein T cell receptor transgenic mice

Autoimmune diseases result from a failure of tolerance. Although many self-reactive T cells are present in animals and humans, their activation appears to be prevented normally by regulatory T cells. In this study, we show that regulatory CD4(+) T cells do protect mice against the spontaneous occurrence of experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis. Anti-myelin basic protein (MBP) TCR transgenic mice (T/R+) do not spontaneously develop EAE although many self-reactive T cells are present in their thymi and peripheral lymphoid organs. However, the disease develops in all crosses of T/R+ mice with recombination-activating gene (RAG)-1 knockout mice in which transgenic TCR-expressing cells are the only lymphocytes present (T/R- mice). In this study, crosses of T/R+ mice with mice deficient for B cells, CD8(+) T cells, NK1.1 CD4(+) T (NKT) cells, gamma/delta T cells, or alpha/beta T cells indicated that alpha/beta CD4(+) T cells were the only cell population capable of controlling the self-reactive T cells. To confirm the protective role of CD4(+) T cells, we performed adoptive transfer experiments. CD4(+) T cells purified from thymi or lymph nodes of normal mice prevented the occurrence of spontaneous EAE in T/R- mice. To achieve full protection, the cells had to be transferred before the recipient mice manifested any symptoms of the disease. Transfer of CD4(+) T cells after the appearance of symptoms of EAE had no protective effect. These results indicate that at least some CD4(+) T cells have a regulatory function that prevent the activation of self-reactive T cells.

Attenuation of Inducible Th2 Immunity with Autoimmune Disease Progression

Autoantigen-based immunotherapeutics have been shown to activate regulatory responses capable of inhibiting T cell-mediated autoimmune disease in animal models. However, their efficacy generally declines, as treatment occurs later in the disease process, and their mechanism of action is a matter of intense debate. Here, we report that the early administration of β cell autoantigens (βCAAs) to nonobese diabetic (NOD) mice broadly diverts the natural development of potentially pathogenic Th1-biased autoimmune responses toward the Th2 phenotype through Th2 spreading. With disease progression, there was a steady decline in the ability of βCAA treatment to promote Th2-type cellular and humoral autoimmunity. Late in the disease process, some βCAAs were still able to induce Th2 responses and Th2 spreading (although to a much lesser extent), while other autoantigens were not. This attenuation of inducible Th2 immunity with disease progression is likely to reflect a reduction in the availability of uncommitted autoantigen-reactive precursor T cells. These findings suggest that there are inherent differences in the frequency of βCAA-reactive T cells and that, in advanced stages of autoimmune disease, regulatory responses may be best elicited with target tissue Ags against which large uncommitted T cell pools are still available. Since individuals presenting the first signs of autoimmune disease are likely to already have an advanced disease process, these findings may be useful for the rational design of Ag-based immunotherapeutics.

In vitro differentiation of peripheral blood T cells towards a type 2 phenotype is impaired in rheumatoid arthritis (RA)

We have examined the capacity of peripheral blood T cells from RA patients to be polarized in vitro towards a type 1 (T1) or a type 2 (T2) phenotype. Peripheral blood T cells from RA patients and from healthy donors were primed by 1 week of culture with soluble OKT3 in the presence of polarizing cytokines. The recovered T cells were restimulated and their cytokine secretion profile determined. Priming of T cells from RA patients in the presence of recombinant (r)IL-2 plus rIL-12 induced a shift towards a TI pattern, characterized by increased production of interferon-gamma, that was more pronounced than in the case of healthy donors. Conversely, priming of T cells from RA patients in the presence of IL-4 failed to induce a shift towards a T2 profile after 1 week, whereas it induced T cells from healthy donors to acquire such a profile characterized by heightened production of IL-4, IL-5 and IL-13. However, a T2 polarization profile emerged in T cells from RA patients that were primed in the presence of rIL-4 and subsequently maintained in culture in rIL-2 alone for 1 or 2 additional weeks. We conclude that in vitro differentiation of peripheral T cells towards a type 2 phenotype is impaired in RA. Nevertheless, conditions required to drive peripheral T cells towards a type 2 phenotype were established. Administration of autologous polyclonal T cells expressing a type 2 cytokine secretion profile is proposed as a therapeutic strategy in RA.

Role of insulin in antigen-induced airway eosinophilia and neuronal M2 muscarinic receptor dysfunction

In the lungs, neuronal M2 muscarinic receptors limit ACh release from parasympathetic nerves. In antigen-challenged animals, eosinophil proteins block these receptors, resulting in increased ACh release and vagally mediated hyperresponsiveness. In contrast, diabetic rats are hyporesponsive and have increased M2 receptor function. Because there is a low incidence of asthma among diabetic patients, we investigated whether diabetes protects neuronal M2 receptor function in antigen-challenged rats. Antigen challenge of sensitized rats decreased M2 receptor function, increased vagally mediated hyperreactivity by 75%, and caused a 10-fold increase in eosinophil accumulation around airway nerves. In antigen-challenged diabetic rats, neuronal M2 receptor function was preserved and there was no eosinophil accumulation around airway nerves. Insulin treatment of diabetic rats completely restored loss of M2 receptor function, vagally mediated hyperresponsiveness, and eosinophilia after antigen challenge. These data demonstrate that insulin is required for development of airway inflammation, loss of neuronal M2 muscarinic receptor function, and subsequent hyperresponsiveness in antigen-challenged rats and may explain decreased incidence of asthma among diabetic humans.

Mature Mainstream TCRαβ+CD4+ Thymocytes Expressing L-Selectin Mediate “Active Tolerance” in the Nonobese Diabetic Mouse

Pathogenic autoreactive T lymphocytes are mediators of spontaneous insulin-dependent diabetes in nonobese diabetic (NOD) mice. This is demonstrated by their capacity to transfer diabetes into syngeneic immunoincompetent recipients. In addition, especially in prediabetic NOD mice, peripheral CD4+ T lymphocytes were identified that are highly effective, in conventional mixing cotransfer experiments, at preventing disease transfer. The present data demonstrate that mature heat-stable Ag−TCRαβ+CD8− thymocytes from prediabetic NOD mice also express this inhibitory capacity. Selection using an L-selectin (CD62L)-specific Ab showed that TCRαβ+CD4+CD62L+ thymocytes, emerging from the mainstream differentiation pathway, concentrate this ability to regulate autoreactive effectors. Compared with mature TCRαβ+CD8− thymocytes, significantly lower numbers of TCRαβ+CD4+CD62L+ were sufficient to achieve an efficient inhibition of disease transfer into NOD-scid recipients. This protective ability was potentiated following in vitro culture in the presence of IL-7. In contrast, TCRαβ+CD62L− thymocytes, highly enriched in class I-restricted NK T cells, were unable to influence diabetes transfer. Identical results were obtained using thymocytes that have been cultured in vitro for 4 days in the presence of IL-7. These results support the active role in NOD mice of a thymus-derived CD4+ subset that controls peripheral pathogenic autoimmune effectors.

A dominant role for non-MHC gene effects in susceptibility to cyclosporin A (CsA)-induced autoimmunity

Lethally irradiated LEW rats reconstituted with syngeneic bone marrow and given CsA for a 4-week period develop a graft-versus-host-like disease upon withdrawal of CsA. This T cell-mediated autoimmune disease is referred to as CsA-induced autoimmunity (CsA-AI). CsA-AI-susceptible LEW rats and resistant BN rats differ greatly in the composition of their peripheral T cell compartment. To dissect the role of MHC and non-MHC genes in the development of peripheral T cell subsets in combination with susceptibility to CsA-AI the respective MHC congenic strains (LEW-1N and BN-1L) were examined for their T cell subsets and for their ability to develop CsA-AI. In this study we show that the Th1/Th2-like cell ratio as well as susceptibility to CsA-AI are under control of the non-MHC genes. This suggests that the Th1/Th2-like cell ratio is a critical determinant for development of CsA-AI. Alternatively, resistance can be attributed to lack of target organ susceptibility due to the absence of the target autoantigen in resistant rat strains. This interpretation is rejected, since both BN as well as BN-1L rats consistently develop the characteristic macroscopic and microscopic signs of CsA-AI upon adoptive transfer with autoreactive LEW-1N and LEW T cells, respectively. Therefore, it can be concluded that the non-MHC genes encode for immune deviation and thereby determine susceptibility or resistance to CsA-AI.

Immunoregulation by CD4 T cells in the induction of specific immunological unresponsiveness to alloantigens in vivo: evidence for a reduction in the frequency of alloantigen-specific cytotoxic T cells in vitro

Donor-specific unresponsiveness to allogeneic cardiac allografts in mice can be induced by the combined pretreatment with donor alloantigen and anti-CD4 antibody (anti-CD4+DST). We have investigated whether the induction of unresponsiveness in this model is due to the presence of T cells that regulate immune responsiveness towards the allograft. First, we analysed the functional characteristics of splenocytes from pretreated mice at the time of transplantation. A significant reduction in the frequency of donor specific cytotoxic precursor was found only after the anti-CD4+DST treatment. Next, we designed an in vitro assay to identify the phenotype of the splenocyte population responsible. CD4+ and CD4- fractions were purified from mice treated with anti-CD4+DST or anti-CD4 alone (controls) by cell sorting. Interestingly, only the addition of CD4+ cells from anti-CD4+DST treated mice resulted in a selective reduction and a bimodal distribution in the donor specific CTLp response, indicating the presence of a regulatory population. CD4+ cells from controls did not have this effect. These in vitro findings were substantiated by adoptive transfer experiments in vivo. These data demonstrate that CD4+ cells with the ability to regulate immune responsiveness to a cardiac allograft are present at the time of transplantation following pretreatment with donor alloantigen in combination with anti-CD4.

ICAM-1 costimulation induces IL-2 but inhibits IL-10 production in superantigen-activated human CD4+ T cells

We have previously reported that costimulatory pathways including B7-CD28 and lymphocyte function-associated antigen-3 (LFA-3)-CD2 shape distinct activation profiles in human CD4+ T cells. We now show that superantigen (SAg), in combination with intracellular adhesion molecule-1 (ICAM-1) costimulation drives a proliferative response accompanied by high levels of interleukin-2 (IL-2) and moderate levels of interferon-gamma (IFN-gamma) and tumour necrosis factor (TNF). This response profile differs from that observed in B7 or LFA-3 costimulated T cells because our previous results showed that B7-CD28 costimulation was accompanied by high levels of IL-2, IFN-gamma and TNF, whereas LFA-3 was a potent inducer of IFN-gamma and TNF, but had little influence on IL-2 production. The ICAM-1-induced IL-2 production could efficiently be abrogated with monoclonal antibody (mAb) against ICAM-1 or LFA-1, showing that the activation is dependent of a functional ICAM-1-LFA-1 pathway. SAg-induced IL-2, IFN-gamma and TNF were detected in both CD4+ and CD8+ T cells, whereas production of IL-10 was restricted to CD4+ T cells. A major finding in the present study was that ICAM-1 costimulation strongly inhibits IL-10 production in CD4+ T cells. Our data demonstrate that ICAM-1 costimulation is sufficient to induce large amounts of IL-2. The presence of ICAM-1 results in suppression of IL-10 production in T helper (Th) cells, which may favour the development of Th1 and not Th2 T cells.

Are there unique autoantigens triggering autoimmune diseases?

Using three reference disease models--insulin-dependent diabetes mellitus (IDDM) as a prototype of T-cell mediated organ-specific autoimmune disease, myasthenia gravis (MG) as a prototype of autoantibody-mediated organ-specific autoimmune disease and systemic lupus erythematosus (SLE) as a prototype of non-organ-specific autoimmune disease--we have reached several conclusions: 1) All three diseases are associated with the presence of multiple autoantibodies and/or autoreactive T cells that recognize a large number of antigenic molecules. The apparent predominant role of certain antibodies in some diseases could relate to their functional properties such as acetylcholine receptor (AChR) blockade for anti-AChR autoantibodies in MG or anti-dsDNA in SLE. 2) Major target antigens are clustered in the target cell affected by organ-specific autoimmune diseases: beta cells in IDDM, striated-muscle cells in MG, or apoptotic cells in the case of SLE. 3) Antibodies and T cells recognize multiple epitopes in these molecules. 4) The most evident explanation for the observed clustering and diversity is autoantigen spreading. Spreading probably involves T cells secreting proinflammatory cytokines but also possibly antibodies as in the case of nucleosome autoantibodies in SLE. 5) The counterpart of antigen spreading is bystander suppression in which regulatory cytokines deviate the immune response towards a protective response. 6) The mechanisms underlying the initiation of the autoimmune response and antigen spreading are still undetermined. They could imply a direct abnormality of the target cell in the case of organ-specific autoimmune diseases (e.g. infection with a virus showing a selective tropism for the target cell in organ-specific autoimmune diseases, or loss of physiological regulation of major histocompatibility complex molecule expression) or could be consequence of a ubiquitous cell abnormality such as increased apoptosis in SLE. The respective roles of genetic and environmental factors in these triggering events remain to be determined.

CD4+CD25+ immunoregulatory T cells suppress polyclonal T cell activation in vitro by inhibiting interleukin 2 production

Peripheral tolerance may be maintained by a population of regulatory/suppressor T cells that prevent the activation of autoreactive T cells recognizing tissue-specific antigens. We have previously shown that CD4+CD25+ T cells represent a unique population of suppressor T cells that can prevent both the initiation of organ-specific autoimmune disease after day 3 thymectomy and the effector function of cloned autoantigen-specific CD4+ T cells. To analyze the mechanism of action of these cells, we established an in vitro model system that mimics the function of these cells in vivo. Purified CD4+CD25+ cells failed to proliferate after stimulation with interleukin (IL)-2 alone or stimulation through the T cell receptor (TCR). When cocultured with CD4+CD25- cells, the CD4+CD25+ cells markedly suppressed proliferation by specifically inhibiting the production of IL-2. The inhibition was not cytokine mediated, was dependent on cell contact between the regulatory cells and the responders, and required activation of the suppressors via the TCR. Inhibition could be overcome by the addition to the cultures of IL-2 or anti-CD28, suggesting that the CD4+CD25+ cells may function by blocking the delivery of a costimulatory signal. Induction of CD25 expression on CD25- T cells in vitro or in vivo did not result in the generation of suppressor activity. Collectively, these data support the concept that the CD4+CD25+ T cells in normal mice may represent a distinct lineage of "professional" suppressor cells.

Prevention of type 1 diabetes

This article discusses type 1 diabetes mellitus, which results from insulin deficiency caused by autoimmune destruction of the insulin-producing beta-cells in the pancreatic islets of Langerhans. The autoimmune response against islet beta-cells is believed to result from a disorder of immunoregulation. According to this concept, T lymphocytes (T cells) autoreactive to certain beta-cell constituents exist normally but are restrained by regulatory (suppressor) T cells. Activation of beta-cell autoreactive T cells together with deficient regulatory T cell responses is believed to result in clonal expansion of autoreactive T cells, and these cells may elicit a cascade of beta-antigen specific (T cell) immune and nonspecific inflammatory responses that destroy islet beta-cells. Islet beta-cells autoreactive T cells seem to secrete type 1 cytokines, whereas regulatory T cells may secrete type 2 and type 3 cytokines; therefore, type 1 diabetes may result from a relative dominance of type 1 cytokines over type 2 and type 3 cytokines. These concepts derive mainly from studies in animal models with spontaneous autoimmune diabetes, and the evidence in humans with type 1 diabetes is sparse. Nevertheless, the concept of type 1 diabetes as a disorder of immunoregulation has spurred clinical trials of diabetes prevention based on strategies directed at diverting the immune response from autoimmunity to self-tolerance, for example, by administration of beta-cell autoantigens, and by attempting to tip the immune balance in favor of the production or action of type 2 and type 3 cytokines over type 1 cytokines.

Neutralizing TNF-alpha activity modulates T-cell phenotype and function in experimental autoimmune uveoretinitis

Inhibiting TNF-alpha activity prevents tissue destruction without inhibiting retinal T cell infiltration in experimental autoimmune uveoretinitis (EAU) in Lewis rats. To further determine the role of TNF-alpha in autoimmune uveitis we characterized T cells isolated from retinae after treatment with a TNF-alpha antagonist. TNF-alpha activity was neutralized in vivo with a p55 TNF-alpha receptor-Ig fusion protein (sTNFr-Ig), administered 8 and 10 days after induction of EAU with heterologous retinal antigens. Retinal T-cell phenotype expression was examined by flow cytometry with respect to OX22 status (CD45RBlow or CD45RBhigh), activation (OX40 and CD25 expression) and rate of T-cell apoptosis (Annexin V+PI- expression). Lymphocyte reactivity was assessed by proliferation responses and cytokine production to retinal antigens. Despite greater than 40% of CD4+ T cells being activated at the height of disease, the proportion of OX22low expression was reduced and T cells exhibited reduced IFN-gamma and elevated IL-4 production. Retinal T cells maintained antigen-specific proliferation and demonstrated a low apoptotic rate. Although in both animal groups, comparable numbers of T cells were isolated, neutralizing TNF activity suppressed Th1 effector mechanisms protecting against target organ damage.

How do monoclonal antibodies induce tolerance? A role for infectious tolerance?

One of the major goals in therapeutic immunosuppression has been to achieve long-term benefit from short-term therapy. The discovery in the mild-1980s that CD4 antibodies can induce immunological tolerance without depleting CD4+ T cells has reawakened interest in the use of nondepleting monoclonal antibodies for reprogramming the immune system in autoimmunity and in transplantation. Since that time, antibodies to CD11a, CD4OL, CD25, CD3, and CTLA4-Ig have all been shown capable of facilitating tolerance. In order to apply to principle of reprogramming in the clinic, we have sought to understand the mechanisms that are involved in its induction and its maintenance. In a number of allogeneic transplant models (heart, skin, bone marrow) anti-CD4 (+/- CD8) antibodies can be shown to block the rejection process while selectively promoting the development of CD4+ regulatory T cells responsible for a dominant tolerance that is reflected in findings of linked suppression and infectious tolerance. In these models, T cells that have never been exposed to CD4 antibodies become tolerant to grafted antigens by experiencing antigen in the microenvironment of regulatory T cells. Dominant tolerance is not the only mechanism that can be facilitated by CD4 Mab therapy. If allogeneic marrow is given at high cell doses under the umbrella of CD4 and CD8 antibodies, then tolerance can be achieved through clonal deletion. The mechanism by which regulatory CD4+ T cell suppress is not yet defined but could be active or passive. We have proposed the "civil service model" to explain how tolerant T cells might interfere with the responses of competent T cells in such a way as to render them tolerant.

No evidence for involvement of the interleukin-10 -592 promoter polymorphism in genetic susceptibility to primary biliary cirrhosis

BACKGROUND/AIMS

Primary biliary cirrhosis is a chronic cholestatic liver disease with an autoimmune aetiology. Family studies, which have shown a significantly increased incidence of primary biliary cirrhosis in the close relatives of patients, suggest that genetic factors play a significant role in determining disease susceptibility. Several studies have previously identified loci which appear to play a role in determining this susceptibility, including the MHC class II allele HLA DR8, and the class III encoded C4A null allele (C4AQ0). Here, we have studied another candidate susceptibility locus in primary biliary cirrhosis, an apparently functional biallelic polymorphism at position -592 in the promoter region of the gene encoding the immuno-modulatory cytokine interleukin-10. Interleukin-10 plays an important role in the functional control, in vivo, of autoreactive Th-1 type CD4+ T-cells, with experimental manipulation of interleukin-10 leading to significant modulation of disease development in animal models of autoimmunity.

METHODS

Interleukin-10 -592 genotypes were studied by polymerase chain reaction in 171 well-characterised, histologically-staged, primary biliary cirrhosis patients and 141 locally matched controls.

RESULTS

Of 171 primary biliary cirrhosis patients, 99 were homozygous for the commoner allele (C/C), 68/171 (40%) were heterozygotes (A/C), whilst 4/171 (2%) were homozygous for the rarer allele (A/A). These genotype frequencies were not significantly different from those seen in controls (p=0.49, odds ratio 1.2 [0.8-1.91).

CONCLUSIONS

These findings, in the first study of IL-10 as a candidate locus in a human autoimmune disease, suggest that IL-10 -592 is not a susceptibility locus in primary biliary cirrhosis.

Expression of ADP-Ribosyltransferase on Normal T Lymphocytes and Effects of Nicotinamide Adenine Dinucleotide on Their Function

ADP-ribosyltransferase (ADPRT) is a glycosylphosphatidylinositol-anchored cell surface enzyme on CTL. Expression of this enzyme correlates with suppression of CTL functions in the presence of its substrate β-nicotinamide adenine dinucleotide (NAD). To investigate the immunoregulatory importance of ADPRT on normal lymphocytes in vivo, NAD was injected into mice and the effects on cell-mediated and humoral immunity were assessed. Induction of both delayed-type hypersensitivity and CTL, but not Ab responses, are shown to be suppressed by NAD. Consistent with this, mature T cells, but not B cells or macrophages, express ADPRT and are able to ADP-ribosylate cell surface proteins. ADP-ribosylated molecules were identified as LFA-1, CD8, CD27, CD43, CD44, and CD45. Concomitant to ADP-ribosylation of these molecules, T cell trafficking to secondary lymphoid organs is suppressed by NAD. To examine whether this is due to effects of NAD on cell activation, Ag-stimulated responses were assayed in vitro. NAD is shown to inhibit induction of cell proliferation, cytotoxicity, and cytokine secretion. It is suggested that ADPRT regulates T cells on the level of transmembrane signaling via ADP-ribosylation of cell surface molecules. This effect is reported to be indirect, as it involves transmission of signals through TCRs, which are not ADP-ribosylated.

Effects of HgCl2 on the expression of autoimmune responses and disease in diabetes-prone (DP) BB rats

Repeated exposure of Brown Norway (BN) rats to relatively low doses of HgCl2 induces autoantibodies to renal antigens (e.g., laminin) and a membranous glomerulonephropathy characterized by proteinuria. In contrast, Lewis (LEW) rats are "resistant" to the autoimmune effects of mercury and, when exposed to this metal, are protected against experimental autoimmune encephalomyelitis (EAE) and Heymann's nephritis. To date, there is no information on "suppressive" effects of mercury in naturally occurring (so-called "spontaneous") rat models of autoimmune disease. Therefore, we have administered HgCl2 to diabetes-prone (DP) BB rats, animals that spontaneously develop both insulin-dependent diabetes mellitus (IDDM) and thyroiditis. We found that DP rats treated with mercury or water for a period of 40-125 days developed autoantibodies to thyroglobulin, with a higher incidence in HgCl2-injected animals (92% vs. 56% in H2O-injected controls). A novel finding of our study was the detection of autoantibodies to laminin in the same rats, again with an increased incidence after HgCl2 treatment (83% vs. 44%). IgG2a was the most frequently detected isotype of antibodies to laminin, followed by IgG1, IgG2b and IgG2c. The IgG isotype profile suggests that treatment with HgCl2 may activate both Th1 and Th2 lymphocytes in BB rats. In spite of these stimulatory effects on autoantibody responses, we found that there was no difference in the incidence of IDDM and thyroiditis between HgCl2-treated and control animals. We conclude that the suppressive effects of mercury previously observed in EAE and Heymann's nephritis of LEW rats do not occur in "spontaneous" autoimmune IDDM and thyroiditis of BB rats. Therefore, immune suppression caused by HgCl2 cannot be considered a common phenomenon, but may be a genetically determined characteristic of LEW rats, possibly related to a specific or unique cytokine profile of this particular rat strain. In contrast, while mercury does not seem to recruit, induce or rescue regulatory T cell function in DP rats, it does stimulate autoantibody responses in these animals.

Cytokines and their roles in pancreatic islet beta-cell destruction and insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is a disease that results from autoimmune destruction of the insulin-producing beta-cells in the pancreatic islets of Langerhans. The autoimmune response against islet beta-cells is believed to result from a disorder of immunoregulation. According to this concept, a T helper 1 (Th1) subset of T cells and their cytokine products, i.e. Type 1 cytokines--interleukin 2 (IL-2), interferon gamma (IFNgamma), and tumor necrosis factor beta (TNFbeta), dominate over an immunoregulatory (suppressor) Th2 subset of T cells and their cytokine products, i.e. Type 2 cytokines--IL-4 and IL-10. This allows Type 1 cytokines to initiate a cascade of immune/inflammatory processes in the islet (insulitis), culminating in beta-cell destruction. Type 1 cytokines activate (1) cytotoxic T cells that interact specifically with beta-cells and destroy them, and (2) macrophages to produce proinflammatory cytokines (IL-1 and TNFalpha), and oxygen and nitrogen free radicals that are highly toxic to islet beta-cells. Furthermore, the cytokines IL-1, TNFalpha, and IFNgamma are cytotoxic to beta-cells, in large part by inducing the formation of oxygen free radicals, nitric oxide, and peroxynitrite in the beta-cells themselves. Therefore, it would appear that prevention of islet beta-cell destruction and IDDM should be aimed at stimulating the production and/or action of Type 2 cytokines, inhibiting the production and/or action of Type 1 cytokines, and inhibiting the production and/or action of oxygen and nitrogen free radicals in the pancreatic islets.

Inhibition of the development of spontaneous autoimmune thyroiditis in the obese strain (OS) chickens by in vivo treatment with anti-CD4 or anti-CD8 antibodies

The involvement of CD4+ and CD8+ T cells in pathogenesis of spontaneous autoimmune thyroiditis (SAT) in obese strain (OS) chickens has not been studied in depth until now. We depleted CD4+ or CD8+ T cells in OS chickens by treatment with murine monoclonal anti-CD4 or anti-CD8 antibodies at 3 day intervals beginning at hatching. The birds were killed at 19-25 days of age. Treatment with anti-CD4 antibody completely prevented SAT development, while treatment with anti-CD8 antibody partially inhibited SAT. These results show the critical role of CD4+ T cells in the development of SAT in OS chickens, and indicate that CD8+ T cells are also involved in SAT pathogenesis.

Pathogenesis of cyclosporin A-induced autoimmunity: absence of T-cell reactivity towards syngeneic antigen presenting cells

Cyclosporin A-induced autoimmunity (CsA-AI) is a T-cell mediated inflammatory autoimmune disease of the skin resembling human scleroderma and is often referred to as syngeneic-Graft-versus-Host Disease. Induction of CsA-AI is obtained by total body irradiation in combination with syngeneic bone marrow transplantation (BMT) and subsequent administration of CsA for 4 weeks; about 2 weeks after withdrawal of CsA disease develops. In CsA-AI, irradiation is thought to eliminate peripheral autoregulatory T-cells, whereas CsA interferes with selection in the thymus giving rise to putative autoreactive T-cells. MHC class II-self-peptide complexes have been thought to function as autoantigen(s). Moreover, induction of CsA-AI is used in humans to achieve a Graft-versus-Leukemia effect based on this anti-MHC class II reactivity. In this study we therefore have examined whether T-cells of CsA-AI rats respond to syngeneic dendritic cells (DC). Furthermore we determined the in vitro stimulatory capacity of the presumptive antigen presenting cell (APC) in the target organs, i.e. the keratinocytes. In contrast to keratinocytes of control rats the keratinocytes of CsA-AI rats show in situ a strong reactivity with anti-MHC class II specific monoclonal antibody (mAb) and therefore might induce local T-cell activation. Results reveal that T-cells of CsA-AI rats have no increased response to syngeneic DC. This indicates that MHC class II is not the autoantigen and that the autoantigen(s) are not presented by peripheral APC of control animals. With respect to possible APC in the target organ flow cytometry showed a strong induction of MHC class II and upregulation of MHC class I on keratinocytes of CsA-AI rats. However, these cells were unable to give any stimulatory signal to T-cells of control or diseased animals, indicating that the autoantigen(s) are not presented by keratinocytes of CsA-AI rats and that the MHC induction is probably secondary to the inflammatory reaction in the skin. The nature of the autoantigen(s) therefore remains to be determined.

Major histocompatibility class II genes polymorphism in insulin dependent diabetes mellitus with or without associated thyroid autoimmunity

Insulin dependent diabetes mellitus (IDDM) is sometimes associated with extrapancreatic organ-specific autoimmune diseases, but whether this phenotype results from a peculiar genetic profile is still unclear. The allelic distribution of the major histocompatibility complex (MHC) class II genes (HLA-DRB1, DQA1, DQB1 and TAP) was analysed in 143 patients with IDDM alone by comparison with 82 IDDM patients with autoimmune thyroid disease (IDDM/AITD). The frequency of the DQB1*0301 IDDM-protective phenotype seemed to be lower in IDDM than in IDDM/AITD patients (16.8% vs 30.5% respectively, p = 0.02). By contrast, the frequency of the DRB1*04-DQB1*0302 IDDM-predisposing phenotype was higher in IDDM than in IDDM/AITD patients (91.3% vs 76.1% of DR4-positive patients respectively, p = 0.007), but these differences were not significant after correcting the p values, except in the case of the DRB1*0405-DQB1*0302 combination (21.3% vs 2.4% of DR4-positive patients, Pc = 0.05). Furthermore, all differences disappeared when patients were matched for age at IDDM-onset. Our data do not long give support for a particular role of MHC class II genes in favouring the occurrence of thyroid autoimmunity in IDDM patients, but rather suggest that some class II alleles or residues might determine the rapidity of progression to IDDM in genetically susceptible individuals. The involvement of non-MHC genes and/or environmental factors remains to be determined.

Mercury-induced autoimmunity in Brown Norway rats: kinetics of changes in RT6+ T lymphocytes correlated with IgG isotypes of circulating autoantibodies to laminin 1

Repeated exposure to mercury causes various autoimmune effects in rats of the Brown Norway (BN) strain. Previous studies from our laboratory have shown that on day 15 of HgCl2 treatment BN rats exhibit a relative decrease in RT6.2+ T cells. At the same time, they produce high levels of autoantibodies to renal antigens and experience a membranous glomerulonephropathy. In contrast, Lewis (LEW) rats are resistant to autoimmunity caused by mercury and do not demonstrate a decrease in RT6+ cells after administration of HgCl2. In the present paper we provide novel information on the correlation between changes in RT6.2+ lymph node T cells and the production of autoantibodies to laminin 1, obtained by detailed kinetic studies of HgCl2-treated BN rats. We have confirmed a decrease in the percentage of RT6.2+ lymphocytes on day 15 of mercury treatment, despite a significant increase in the number of peripheral lymphocytes. No such changes were observed in LEW rats. We have determined that on day 15 the percentage decrease in RT6+ cells is evident in both RT6.2+CD4+ and RT6.2+CD8+ T cell subsets. Kinetic studies demonstrated that significant changes in the percentage of RT6.2+ cells are first observed by day 8 and continue through days 11 and 15. We have also observed a significant percent decrease in CD4+ T lymphocytes as well as an increase in CD4-CD8- cells. The dramatic increase in the percentage of these double negative cells at the level of peripheral lymphoid tissues does not appear to be due to higher thymic output, since there was a decrease in the percentage of TCR+Thy1+ cells, a phenotype that is associated with recent thymic emigrants. Finally, we have demonstrated that 100% of HgCl2-treated BN rats had circulating antibodies that reacted with both mouse and rat laminin 1, i.e. are autoantibodies to laminin 1. These autoantibodies were predominantly of the IgG1 and IgG2a isotype, possibly as the result of a polarized autoimmune response driven by Type 2 cytokines. A kinetic investigation showed that significant levels of IgG1 and IgG2a autoantibodies to laminin 1 were first presentin the circulation by day 11. The inverse correlation between levels of RT6.2+ T lymphocytes and autoantibodies to laminin 1 suggests that mercury may induce autoimmune responses in BN rats by its effects on these immunoregulatory cells.

Administration of IL-4 prevents autoimmune diabetes but enhances pancreatic insulitis in NOD mice

The present study demonstrated that the administration of recombinant interleukin-4 (rIL-4) prevented overt diabetes in nonobese diabetic (NOD) mice whose T cells produced relatively low amounts of IL-4. However, massive insulitis was observed in rIL-4-treated NOD mice. The flow cytometric analysis of islet-infiltrating T cells revealed that the number of CD45RBlowCD4+ T cells was significantly increased by in vivo administration of rIL-4. By measuring the cytokine production of splenic T cells after stimulation, it was shown that CD45RBlowCD4+ T cells predominantly produced IL-4 and IL-10 but produced less IL-2 and interferon-gamma (IFN-gamma). A semiquantitative reverse-transcriptase polymerase chain reaction assay revealed a higher expression of IL-4 and IL-10 mRNA and an apparent decrease in IFN-gamma mRNA in the islets of NOD mice which were administered rIL-4. These results suggested that autoreactive CD45RBlowCD4+ T helper 2 (Th2)-like cells which developed following rIL-4 administration were predominant in the infiltrate of the islets, and overt diabetes was prevented. On the other hand, when splenocytes from rIL-4-treated NOD mice were transferred to irradiated NOD recipients, along with splenocytes from diabetic NOD mice, all of the recipient mice became diabetic within 8 weeks after transfer. Considered together, a supplement of rIL-4 administered to NOD mice may protect against autoimmune diabetes by facilitating the development of Th2-like autoreactive T cells in the islets.

Th1-like cytokine production profile and individual specific alterations in TCRBV-gene usage of T cells from newly diagnosed type 1 diabetes patients after stimulation with beta-cell antigens

In order to study cytokine production profile (IFN-gamma, IL-4 and TNF-alpha) and TCRBV-gene usage of peripheral autoreactive T cells from IDDM patients, we have generated antigen-specific T cell lines with either tetanus toxoid, insulinoma membranes or a single beta-cell protein, recombinant ICA69, which has been shown to be a target of both autoantibodies and T cells in IDDM. By semi-quantitative polymerase chain reaction (PCR) analysis, we have determined the composition of the T cell receptor repertoire of these T cell lines and compared this with the general peripheral repertoire. T cell responses against beta-cell antigens and tetanus toxoid (TT) were shown to be associated with IFN-gamma and TNF-alpha production, suggestive of a Th1-like phenotype of the T-cell lines. The production of IFN-gamma was significantly higher in T-cell lines generated with ISG compared to those generated with TT. The cytokine production profiles of the T-cell lines generated with ICA69 did not provide an obvious explanation for the inverse relation between cellular and humoral responses to this protein observed earlier. Upon stimulation with beta-cell antigens, outgrowth of T cells using a restricted set of TCRBV elements was observed in newly diagnosed IDDM patients. However, this skewing in TCRBV-gene expression was patient-specific rather than antigen-associated, since the T-cell repertoire that is used for the recognition of these antigens was, overall, heterogeneous.

NOD fetal thymus organ culture: an in vitro model for the development of T cells involved in IDDM

This paper introduces a model which incorporates fetal thymus organ culture (FTOC) from NOD mice to replicate thymic development of diabetogenic T cells. NOD fetal pancreas organ culture (FPOC) co-cultured with 13-16 day NOD FTOC for an additional 14-21 days produced less insulin than FPOC cultured alone. Insulin production from the FTOC of non-diabetic strains C57BL/6 and BALB/c was not inhibited by co-culture with FTOC from their syngeneic counterparts. Sections of the NOD co-cultures showed peri-islet infiltration with lymphocytes. Insulin reduction by FTOC/FP co-culture was prevented by co-culture of the NOD FT with FT from immunologically incompetent C.B-17 SCID/SCID mice. Co-culture of NOD FP with NOD FT prior to the development of T cells prevented generation of diabetogenic FTOC. Thus, early exposure of NOD T cell precursors to the thymic stromal elements of C.B-17 SCID/SCID FT or to islet antigens can negatively select for diabetogenic T cells or activate immuno-regulatory cells that can suppress diabetogenic T cell activity. The addition of blocking F(ab')2 fragments of anti-CD3epsilon monoclonal antibody to NOD FTOC/FP co-cultures prevented insulin reduction, implicating a role for TcR-mediated recognition in this "in vitro IDDM" model. The addition of activating whole anti-CD3epsilon caused the complete ablation of insulin production in FTOC/FP co-cultures from all strains tested. Transfer of unprimed syngeneic FTOC cells to prediabetic NOD mice prevented the onset of IDDM while transfer of islet-cell primed FTOC/FP cells slightly increased disease incidence. These data suggest that while diabetogenic T cells are present in the FT, they are normally suppressed, even after organ culture. However, these cells can induce the destruction of islet cells, in vitro and in vivo, if they are appropriately activated with pancreatic tissue.

Cytokines and Graves' disease

Cytokines are an extraordinarily diverse group of molecules, with pleiotropic and often overlapping effects. They are crucial to the autoimmune response, and, in particular, regulation of CD4+ and CD8+ T-cell function depends on the balance of cytokines produced during an immune response. It is also now clear that cytokines are produced by a wide array of cells, including the thyroid follicular cells (TFCs). Intrathyroidal lymphocytes produce a heterogeneous pattern of cytokines and we have summarized the likely effects of these. In Graves' disease, TFCs can themselves express immunologically important molecules as the result of cytokine stimulation and these could contribute to the perpetuation of the autoimmune process. In addition, cytokines have a number of generally inhibitory effects on thyroid hormone production which would tend to counter the stimulatory effects of thyroid-stimulating hormone receptor antibodies in Graves' disease.

Deviation of pancreas-infiltrating cells to Th2 by interleukin-12 antagonist administration inhibits autoimmune diabetes

Nonobese diabetic (NOD) mice develop spontaneous insulin-dependent diabetes mellitus (IDDM), and the pancreas-infiltrating T cells invariably show a Th1 phenotype. We demonstrated here that the interleukin (IL)-12 antagonist (p40)2 can deviate the default Th1 development of naive T cell receptor (TCR)-transgenic CD4+ cells to the Th2 pathway in vitro. Although (p40)2 does not modify the cytokine profile of polarized Th1 cells, it prevents further recruitment of CD4- cells into the Th1 subset. To study the involvement of Th1 and Th2 cells in the initiation and progression of IDDM, we targeted endogenous IL-12 by administration of (p40)2 in NOD mice. (p40)2 administration to NOD mice inhibits interferon-gamma but not IL-10 production in response to lipopolysaccharide (LPS) or to the putative autoantigen IA-2. Serum immunoglobulin isotypes determined after (p40)2 treatment indicate an increase in Th2 and a decrease in Th1 helper activity. Administration of (p40)2 from 3 weeks of age onwards, before the onset of insulitis, results in the deviation of pancreas-infiltrating CD4+ but not CD8+ cells to the Th2 phenotype as well as in the reduction of spontaneous and cyclophosphamide-accelerated IDDM. After treating NOD mice with (p40)2 from 9 weeks of age, when insulitis is well established, few Th2 and a reduced percentage of Th1 cells are found in the pancreas. This is associated with a slightly decreased incidence of spontaneous IDDM, but no protection from cyclophosphamide-accelerated IDDM. In conclusion, deviation of pancreas-infiltrating CD4+ cells to Th2 is associated with protection from IDDM. However, targeting IL-12 after the onset of insulitis, when the pancreas contains polarized Th1 cells, is not sufficient to induce an effective immune deviation able to significantly modify the course of disease.

Mechanism underlying counterregulation of autoimmune diabetes by IL-4

Diabetes in nonobese diabetic (NOD) mice is an autoimmune disease characterized by the destruction of the beta cells in the pancreas. We have previously reported that transgenic expression of interleukin-4 (IL-4) counterregulates the disease process, completely protecting NOD mice from insulitis and diabetes. Here we demonstrate the presence of autoreactivity but lack of pathogenicity of the IL-4-regulated lymphocytes. The importance of T cell diversity for the protective effect of IL-4 is demonstrated through breeding with transgenic BDC2.5 mice, which have an almost exclusively monoclonal T cell repertoire. Limitation of T cell diversity abrogated the protection by IL-4. We suggest that "immune deviation" in NOD-IL-4 mice is mediated by the pancreatic tissue itself, which causes activation of distinct, nonpathogenic T cell specificities.

DNA vaccines for the treatment of autoimmune disease

DNA vaccines represent one of the most significant developments in vaccine technology in recent years. Although, in general, studies have primarily focused on the induction of protective immune responses against infectious pathogens, the technology may prove useful for other immune-related diseases, including autoimmunity. Autoimmune disease results from a breakdown in tolerance to self antigens; however, the same fundamental immunological reactions that control immune responses to foreign antigens are also likely to operate during the course of autoimmune disease. These include the reciprocal regulation of Th cell subsets. Th1 cells appear to be involved in many organ-specific autoimmune diseases while suppression of disease is associated with cells of the Th2 phenotype. It has been possible, therefore, to suppress many of the pathological consequences of autoimmunity by manipulating the Th1/Th2 cell balance. The induction of Th2 responses by DNA immunization might therefore be expected to have a profound effect on the course of autoimmune disease. Indeed, we have demonstrated that DNA immunization can protect animals against the autoimmune central nervous system inflammatory disease, experimental autoimmune encephalomyelitis (EAE). As many other autoantigens have now been identified, the application of this technology to other autoimmune diseases warrants investigation.

Class I-restricted cross-presentation of exogenous self-antigens leads to deletion of autoreactive CD8(+) T cells

In this report, we show that cross-presentation of self-antigens can lead to the peripheral deletion of autoreactive CD8(+) T cells. We had previously shown that transfer of ovalbumin (OVA)-specific CD8(+) T cells (OT-I cells) into rat insulin promoter-membrane-bound form of OVA transgenic mice, which express the model autoantigen OVA in the proximal tubular cells of the kidneys, the beta cells of the pancreas, the thymus, and the testis of male mice, led to the activation of OT-I cells in the draining lymph nodes. This was due to class I-restricted cross-presentation of exogenous OVA on a bone marrow-derived antigen presenting cell (APC) population. Here, we show that adoptively transferred or thymically derived OT-I cells activated by cross-presentation are deleted from the peripheral pool of recirculating lymphocytes. Such deletion only required antigen recognition on a bone marrow-derived population, suggesting that cells of the professional APC class may be tolerogenic under these circumstances. Our results provide a mechanism by which the immune system can induce CD8(+) T cell tolerance to autoantigens that are expressed outside the recirculation pathway of naive T cells.

Strain variation in susceptibility to monoclonal antibody-induced transplantation tolerance

BACKGROUND

We have reproducibly induced specific tolerance to multiple minor histocompatibility antigens with nondepleting anti-CD4 and -CD8 monoclonal antibodies. The tolerance induced is effective for the lifetime of the host. We have tested this therapy in a number of mouse strain combinations to further understand the mechanisms.

METHODS

Various mouse strains were grafted with allogeneic tail skin with and without nondepleting CD4- and CD8-specific monoclonal antibody therapy. The grafts were monitored daily for signs of rejection.

RESULTS

Whereas the CBA/Ca (H2k) strain can be made tolerant to skin grafts that are mismatched at multiple minor histocompatibility antigens indefinitely, using the same protocol, long-term survival of similarly mismatched grafts on the HW80 (B6 congenic for BALB H1) mouse strain is limited to around 8 weeks. Interestingly, the B10.BR strain, which is also of the H2k haplotype, is also not readily tolerized. In addition, an F1 between the CBA/Ca and the resistant B10.BR strains is B10.BR-like in its susceptibility to tolerance induction. Susceptibility to such antibody-dependent tolerance induction is not related to immunogenicity because grafts mismatched at only a single minor antigen also do not reproducibly survive beyond 8 weeks when grafted onto HW80 mice in the presence of the antibody therapy.

CONCLUSIONS

The data strongly suggest that the B6/B10 genetic background confers a level of resistance to CD4- and CD8-specific monoclonal antibody-dependent tolerance induction.

Cytokines and the pathogenesis of myasthenia gravis

Myasthenia gravis (MG) and its animal model experimental autoimmune myasthenia gravis (EAMG) are caused by autoantibodies against nicotinic acetylcholine receptor (AChR) in skeletal muscle. The production of anti-AChR antibodies is mediated by cytokines produced by CD4+ and CD8+ T helper (Th) cells. Emerging investigations of the roles of cytokines in MG and EAMG have revealed that the Th2 cell related cytokine interleukin 4 (IL-4), an efficient growth promoter for B-cell proliferation and differentiation, is important for anti-AChR antibody production. IL-6 and IL-10 have similar effects. The Th1 cytokine IFN-gamma is important in inducing B-cell maturation and in helping anti-AChR antibody production and, thereby, for induction of clinical signs and symptoms. Results from studies of time kinetics of cytokines imply that IFN-gamma is more agile at the onset of EAMG, probably being one of the initiating factors in the induction of the disease, and IL-4 may be mainly responsible for disease progression and persistance. Even though other Th1 cytokines like IL-2, tumor necrosis factor alpha (TNF-alpha), and TNF-beta as well as the cytolytic compound perforin do not directly play a role in T-cell-mediated help for anti-AChR antibody production, they are actually involved in the development of both EAMG and MG, probably by acting in concert with other cytokines within the cytokine network. In contrast, transforming growth factor beta (TGF-beta) exerts immunosuppressive effects which include the down-regulation of both Th1 and Th2 cytokines in MG as well as EAMG. Suppressive effects are also exerted by interferon alpha (IFN-alpha). Based on elucidation of the role of cytokines in EAMG and MG, treatments that up-modulate TGF-beta or IFN-alpha and/or suppress cytokines that help B-cell proliferation could be useful to improve the clinical outcome.

Diversification of T cell responses to carboxy-terminal determinants within the 65-kD heat-shock protein is involved in regulation of autoimmune arthritis

The T cell response to the 65-kD mycobacterial heat-shock protein (Bhsp65) has been implicated in the pathogenesis of autoimmune arthritis. Adjuvant arthritis (AA) induced in the Lewis rat (RT-1(l)) by injection of Mycobacterium tuberculosis serves as an experimental model for human rheumatoid arthritis (RA). However, the immunological basis of regulation of acute AA, or of susceptibility/resistance to AA is not known. We have defined the specificity of the proliferative T cell responses to Bhsp65 during the course of AA in the Lewis rat. During the early phase of the disease (6-9 d after onset of AA), Lewis rats raised T cell responses to many determinants within Bhsp65, spread throughout the molecule. Importantly, in the late phase of the disease (8-10 wk after onset of AA), there was evidence for diversification of the T cell responses toward Bhsp65 carboxy-terminal determinants (BCTD) (namely, 417-431, 441-455, 465-479, 513-527, and 521-535). Moreover, arthritic rats in the late phase of AA also raised vigorous T cell responses to those carboxy-terminal determinants within self(rat) hsp65 (Rhsp65) that correspond in position to the above BCTD. These results suggest that the observed diversification is possibly triggered in vivo by induction of self(Rhsp65)-reactive T cells. Interestingly, another strain of rat, the Wistar Kyoto (WKY/NHsd) rat (RT-1(l)), with the same major histocompatibility complex class II molecules as the Lewis rat, was found to be resistant to AA. In WKY rats, vigorous responses to the BCTD, to which the Lewis rat responded only in the late phase of AA, were observed very early, 10 d after injection of M. tuberculosis, Strikingly, pretreatment with the peptides comprising the set of BCTD, but not its amino-terminal determinants, provided significant protection to naive Lewis rats from subsequent induction of AA. Thus, T cell responses to the BCTD are involved in regulating inflammatory arthritis in the Lewis rat and in conferring resistance to AA in the WKY rat. These results have important implications in understanding the pathogenesis of RA and in devising new immunotherapeutic strategies for this disease.

Signaling thresholds and interclonal competition in preimmune B-cell selection

The need to eliminate autoreactive B cells must be checked against the need for a diverse B-cell repertoire. Protein tyrosine phosphatases SHP1 and CD45 act antagonistically within B cells to set the threshold level of antigen-receptor engagement required for B-cell elimination. The fate of B cells binding weak autoantigens is also regulated by interclonal competition. In the presence of a normal diverse repertoire of competitor B cells, the autoantigen-binding cells are excluded from follicles in spleen and lymph nodes and undergo rapid cell death. In the absence of interclonal competition, the autoreactive cells enter the follicular microenvironment and survive. A model in which B cells compete for access to limiting follicular niches in order to survive is discussed.

Characterization of mouse Rt6.1 NAD:arginine ADP-ribosyltransferase

Rat RT6 proteins, and perhaps mouse Rt6, identify a set of immunoregulatory T lymphocytes. Rat RT6.1 (RT6.1) and rat RT6.2 (RT6. 2) are NAD glycohydrolases, which catalyze auto-ADP-ribosylation, but not ADP-ribosylation of exogenous proteins. Mouse Rt6.1 (mRt6.1) also catalyzes auto-ADP-ribosylation. The activity of mouse cytotoxic T lymphocytes is reportedly inhibited by ADP-ribosylation of surface proteins, raising the possibility that mRt6 may participate in this process. The reactions catalyzed by mRt6, would, however, need to be more diverse than those of the rat homologues and include the ADP-ribosylation of acceptors other than itself. To test this hypothesis, mRt6.1 and rat RT6.2 were synthesized in Sf9 insect cells and rat mammary adenocarcinoma (NMU) cells. mRt6.1, but not rat RT6.2, catalyzed the ADP-ribosylation of guanidino-containing compounds (e.g. agmatine). Unlike RT6.2, mRt6.1 was a weak NAD glycohydrolase. In the presence of agmatine, however, the ratio of [adenine-14C]ADP-ribosylagmatine formation from [adenine-14C]NAD to [carbonyl-14C]nicotinamide formation from [carbonyl-14C]NAD was approximately 1.0, demonstrating that mRt6.1 is primarily a transferase. ADP-ribosylarginine hydrolase, which preferentially hydrolyzes the alpha-anomer of ADP-ribosylarginine, released [U-14C]arginine from ADP-ribosyl[U-14C]arginine synthesized by mRT6.1, consistent with the conclusion that mRt6.1 catalyzes a stereospecific Sn2-like reaction. Thus, mRt6.1 is an NAD:arginine ADP-ribosyltransferase capable of catalyzing a multiple turnover, stereospecific Sn2-like reaction.