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

Immunologically ignorant autoreactive T cells, epitope spreading and repertoire limitation

The factors that may cause antigen-presenting cells to alter the pattern of protein processing and presentation to autoreactive T cells, and thereby stimulate autoimmune disease, are currently under debate. In this article, Chris Elson and colleagues suggest that cytokines associated with T helper 1 (Th1) cells alter the processing of proteins and that this effect can be counteracted by Th2-associated cytokines.

The basis of autoimmunity: Part I. Mechanisms of aberrant self-recognition

In this two-part series, Argyrios N. Theofilopoulos summarizes the current state of affairs in the field of autoimmunity. Part I integrates the collective mechanistic theories of autoimmune diseases. The most straightforward explanation to emerge with regard to organ-specific diseases is the concept that these are caused by inappropriate, yet conventional, immunological responses against self-antigens for which tolerance has never been established. A similar mechanism may be operative in systemic autoimmunity, but other abnormalities such as defects in the apoptosis machinery may also be invoked. Part II will address the genetic contributions predisposing to autoimmune syndromes.

CD4+ T cell subsets defined by isoforms of CD45 in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune condition characterized by destruction of the intrahepatic bile ducts. Autoreactive CD4+ T cells have been reported both in the peripheral circulation and in the mononuclear cell infiltrate in the affected portal tracts. In this large study we have used two- and three-colour flow cytometry to determine the phenotypes of the CD4+ T cell subsets in the peripheral blood and liver-infiltrating lymphocytes of PBC patients (n = 43), normal controls (n = 19) and patients with alcoholic cirrhosis (n = 15), according to a novel classification based on the simultaneous expression of different isoforms of CD45. In PBC patients the proportion of peripheral blood CD4+ cells possessing the CD45ROhighRA- 'memory' phenotype was significantly increased, and the CD45RO-RAhigh 'naive' population was significantly decreased, compared with the two control groups. No significant differences in peripheral blood CD4+ T cell subsets were seen between patients with pre-cirrhotic and cirrhotic PBC. A similar, but more marked, shift towards the CD45ROhighRA- 'memory' phenotype was seen in the liver-infiltrating CD4+ T cells in PBC patients compared with alcoholic cirrhotics. Cells within the CD4+ memory subpopulation were further subgrouped according to expression of CD45RB, the level of expression of which has been associated with functional differences in the memory subset. In peripheral blood no differences were seen between PBC patients and controls with respect to the proportion of CD45ROhighRBhigh and CD45ROhighRBdim memory subsets. A statistically significant difference in the distribution of these memory subsets, with an increased memory-2/memory-1 ratio was observed in the liver-infiltrating CD4+ T cells of PBC patients compared with those from alcoholic cirrhotic patients. The potential implications of this observation are discussed.

The function of the CD4 coreceptor in the development of T cells

T cells with helper activity can be found in mice that lack expression of the CD4 glycoprotein. The CD4 promoter is active in these cells; they respond to antigens presented by MHC class II molecules; they do not express CD8 and they do not depend on MHC class I for their development. By such criteria, these CD8- T cells resemble normal CD4+ helper T cells. The development of the helper lineage in CD4-null mice can be potentiated by expression of transgenes that encode either wild type CD4, or a deletion mutant of CD4 that lacks the cytoplasmic tail and therefore cannot interact with the tyrosine kinase p56lck. These observations suggest that CD4 is not absolutely required for the specification of the helper cell lineage. The role of the CD4 molecule in the development of T cells and possible mechanisms by which it achieves its functions are discussed.

Central tolerance of T cells

The immune system is constructed to tolerate self antigens but give vigorous responses to foreign antigens. How this state of self/nonself discrimination is maintained is controversial. In the case of T cells, many self antigens are transported to the thymus via the bloodstream and induce tolerance (clonal deletion) of self-reactive thymocytes in situ. Although such central tolerance in the thymus is well documented, it is often argued that full induction of tolerance requires peripheral mechanisms such as suppression or induction of anergy. This article proposes that steady-state tolerance of T cells to self components is due solely to central tolerance to circulating self antigens combined with sequestration of tissue-specific antigens. Backup mechanisms for tolerance do exist but such immunoregulation only operates when self tolerance breaks. This scheme allows the immune system to give unrestricted primary responses to foreign antigens.

Th1 and Th2 CD4+ T cells in the pathogenesis of organ-specific autoimmune diseases

CD4+ T cells play a key role in regulating immune system function. When these regulatory processes go awry, organ-specific autoimmune diseases may develop. Here, Roland Liblau, Steven Singer and Hugh McDevitt explore the thesis that a particular subset of CD4+ T cells, namely T helper 1 (Th1) cells, contributes to the pathogenesis of organ-specific autoimmune diseases, while another subset, Th2 cells, prevents them.

T cells from BB-DP rats show a unique cytokine mRNA profile associated with the IDDM1 susceptibility gene, Lyp

Diabetes prone biobreeding rats display several abnormalities in T cell numbers, T cell function and T cell surface phenotype which are associated with the onset of spontaneous disease. One of the most pronounced abnormalities in these animals is a marked T cell lymphopenia which is evident in both CD4+ and CD8+ peripheral T cell subsets. To gain a better understanding as to the nature of T cell responses in these animals, we have utilized RT-PCR to analyze the cytokine mRNA profiles of mitogen activated peripheral T cells derived from lymphopenic and non-lymphopenic animals. Our results suggest that inheritance of the lymphopenia gene, Lyp, is associated with a unique cytokine profile most similar to that previously described for mouse medullary thymocytes. In addition, cell surface staining of peripheral T cells from diabetes prone animals revealed a high frequency of Thyl+ cells, which is characteristic of both thymocytes and recent thymic emigrants. Following thymectomy, T cell responsiveness to a number of different stimuli is greatly reduced on a cell for cell basis as is the absolute number of surviving T cells. Taken collectively, our results suggest that the majority of the peripheral T cell pool in these diabetic prone rats consists of short lived, recent thymic emigrants which most likely also contain the effector cells required for initiation of diabetes.

Thymic epithelial defects and predisposition to autoimmune disease in BB rats

We report an association between thymic epithelial defects and predisposition to autoimmunity. Diabetes-prone (DP) BB rats develop spontaneous hyperglycemia and are deficient in T cell subsets expressing the RT6 alloantigen. Diabetes resistant (DR) BB rats become diabetic if depleted of RT6+ T cells. The inciting immune system defects are unknown. We made the following observations: 1) Regions of thymic cortex and medulla devoid of thymic epithelium exist in DP-BB, DR-BB, and Lewis rats, all of which are susceptible to autoimmune disorders. Such defects were absent in eight normal rat strains. 2) Thymic epithelial defects are absent at birth, but present in BB rats at 4 weeks of age. 3) The genetic predisposition to thymic epithelial defects is an autosomal dominant trait. 4) The observation of thymic defects in (DP x WF)F1 rats led to the prediction that such animals, which never develop spontaneous autoimmunity, might be susceptible to its induction. Following depletion of RT6+ T cells we observed diabetes in 91%, and thyroiditis in 43%, of treated F1 animals (n = 23). Pancreatic insulitis was uniformly present. Because thymic epithelium participates in the positive and negative selection of developing thymocytes, we propose that thymic epithelial defects may play an important role in the predisposition of BB rats to autoimmunity.

Mechanisms in CD4 antibody-mediated transplantation tolerance: kinetics of induction, antigen dependency and role of regulatory T cells

CBA/Ca mice may be made tolerant to minor histoincompatible B10.BR skin grafts by treatment with a short course of non-depleting anti-mouse CD4 and CD8 monoclonal antibodies (mAb), during the transplantation period. We wished to determine when, in relation to antibody therapy, the T cells became tolerant. This was investigated by a series of adoptive transfer experiments in which mAb-treated cells were removed from therapeutic antibody at defined times after skin grafting, and exposed to fresh antigen in the absence of further mAb treatment. We show here that T cells do not become fully tolerant until 5 weeks after skin grafting. If antibody therapy is continued for the full 5 weeks, T cell tolerance can still be established, suggesting that antibody therapy does not prevent lymphocytes from registering the presence of antigen. Once the tolerant state is established, it is difficult to break that tolerance by lymphocyte infusions from normal donors. This "resistance" is mediated by T cells of the tolerant host. We show that the maintenance of both tolerance and "resistance" requires a continuous supply of antigen. When tolerant cells were "parked" in T cell-depleted mice, tolerance and "resistance" were eventually lost by 6 months. In contrast, "parked" cells exposed to fresh antigen at any time up to 4 months remained tolerant and "resistant" indefinitely. Finally, we wished to establish whether "resistance" was peculiar to this form of peripheral tolerance, or whether it might also be present in tolerance considered to be classically central. We observed resistance to be greater in the mAb-treated peripherally tolerant group, but noted that some of the centrally tolerant animals also exhibited a level of resistance above that of T cell-ablated controls. This suggests that a tolerance mechanism whose role is only minor in central tolerance may have a major role in antibody-mediated peripheral tolerance.

IDDM: an islet or an immune disease?

Insulin-dependent diabetes develops as a consequence of the selective destruction of insulin-producing cells by an autoimmune reaction. However, the precise series of events which trigger anti-islet autoreactive T cells is still being investigated. Major issues will need to be raised before a comprehensive view of the anti-islet autoimmune reaction can be delineated. These include defining the primary site of activation of autoreactive lymphocytes and exploring hypotheses to explain the chronicity of the diabetes process. These issues all relate with the more general dilemma of the actual role of the islets of Langerhans in breaking self tolerance to beta-cell antigens. By studying non-obese diabetic mice deprived of beta cells following a single injection of a high dose of alloxan at 3 weeks of age, we recently obtained evidence that the activation of autoreactive T cells requires the presence of target islet cells in order to develop.

Neonatal injections of cyclosporin enhance autoimmune diabetes in non-obese diabetic mice

Since the modulation of the immune system at birth may influence the course of insulin-dependent (type 1) diabetes, we investigated whether neonatal injections of cyclosporin (CsA) to newborn non-obese diabetic (NOD) mice influence diabetes during later life. Two groups of 90 mice (45 female, 45 male) were injected intraperitoneally for the first 6 days of life with CsA (10 mg/kg per day) or with vehicle. In female NOD mice, the onset of diabetes was earlier and cumulative incidence was higher after neonatal treatment with CsA (P < 0.01). The incidence of diabetes was also dramatically enhanced in male NOD mice (P < 0.01), which normally display a very low disease incidence. Concomitantly, the severity of lymphocytic infiltration of the pancreatic islets was higher in female NOD mice neonatally treated by CsA (P < 0.02), and to a lesser extent in males, than in control mice. After administration of CsA to newborn NOD mice, there was a reduction (P < 0.01) of both CD4+CD8- and CD4-CD8+ thymocytes, whereas the number of double positive CD4+CD8+ thymocytes was increased. Concomitantly, Thy1-2+ cells in spleen were decreased (P < 0.01), and spleen cells expressing either CD3 molecule or alpha beta TCR complex were diminished (P < 0.01). Both CD4+ and CD8+ spleen T cells were depleted. By contrast, the low percentage of gamma delta TCR-expressing splenocytes was not modified. Numbers of MHC class 1+ or MHC class 2+ spleen cells were also depressed (P < 0.01). After neonatal injections of CsA, spleen cells showed a reduced response to concanavalin A (Con A) (P < 0.01). On the contrary, stimulation indices of splenocytes incubated with xenogeneic insulin-producing cell extracts were enhanced (P < 0.03). Proliferation indices of splenocytes to self class 2 antigens, generating suppressor cell activity, during syngeneic mixed lymphocyte reaction (SMLR) were significantly reduced (P < 0.01). Irradiated NOD mice were used as recipients for spleen cells from CsA-neonatally treated NOD mice. They displayed enhanced insulitis 2 weeks after transfer, and diabetes was successfully produced by 1 month after transfer in 50% of the recipients. By contrast, NOD mice which received control syngeneic spleen cells remained normoglycaemic, with only moderate islet infiltration which would be expected of NOD mice of this age. Thus, neonatal injections of CsA markedly enhance diabetes in both female and male NOD mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Inflammatory cells, microglia and MHC class II antigen-positive cells in the spinal cord of Lewis rats with acute and chronic relapsing experimental autoimmune encephalomyelitis

Chronic relapsing experimental autoimmune encephalomyelitis (CR-EAE) was induced in Lewis rats by inoculation with guinea pig spinal cord and adjuvants and treatment with low dose cyclosporin A (CsA). Acute EAE was induced by the same method without CsA treatment. Immunocytochemistry and flow cytometry were used to assess inflammatory cells and MHC class II (Ia) antigen expression in the central nervous system of these rats. The inflammatory infiltrate was composed mainly of CD4+ T cells and macrophages, and alpha beta T cells constituted about 65% of the CD2+ T cells. After recovery from acute EAE and during the first remission of CR-EAE, the number of T cells was significantly less than in the preceding episodes. The number of T cells was higher in the second episode of CR-EAE than in the first remission. Throughout the course of CR-EAE, the majority of the CD2+ T cells were CD45RC-. The ratio of IL-2R+ cells to CD2+ cells ranged from 10.5 to 24.0%. The ratio of CD4+ T cells to B cells was lower in the later episodes of CR-EAE than in the first episode. Ia antigen was expressed on infiltrating round cells at all stages of CR-EAE and on microglial cells (identified by dendritic morphology) with increasing intensity throughout the course of CR-EAE. With flow cytometry, the number of Ia+ cells obtained from the spinal cord rose throughout the course of CR-EAE. The number of FSClowOX1low cells, which we consider represent microglia, also increased during the course of CR-EAE.

A role for non-MHC genetic polymorphism in susceptibility to spontaneous autoimmunity

Peripheral immunological tolerance is traditionally explained by mechanisms for deletion or inactivation of autoreactive T cell clones. Using an autoimmune disease model combining transgenic mice expressing a well-defined antigen, influenza hemagglutinin (HA), on islet beta cells (Ins-HA), and a T cell receptor transgene (TCR-HNT) specific for a class II-restricted HA peptide, we demonstrate that the conventional assumptions do not apply to this in vivo situation. Double transgenic mice displayed either resistance or susceptibility to spontaneous autoimmune disease, depending on genetic contributions from either of two common inbred mouse strains, BALB/c or B10.D2. Functional studies on autoreactive CD4+ T cells from resistant mice showed that, contrary to expectations, neither clonal anergy, clonal deletion, nor receptor desensitization was induced; rather, there was a non-MHC-encoded predisposition toward differentiation to a nonpathogenic effector (Th2 versus Th1) phenotype. T cells from resistant double transgenic mice showed evidence for prior activation by antigen, suggesting that disease may be actively suppressed by autoreactive Th2 cells. These findings shed light on functional aspects of genetically determined susceptibility to autoimmunity, and should lead to new therapeutic approaches aimed at controlling the differentiation of autoreactive CD4+ effector T cells in vivo.

Evidence of CD4+ regulatory T cells in the non-obese diabetic male mouse

The NOD mouse, which shows many features of human IDDM, is extensively used to evaluate the role of T lymphocytes in the pathogenesis of autoimmune diabetes. The development of diabetes in this model appears to be controlled by a finely tuned immunoregulatory balance between autoaggressive T cells and regulatory immune phenomena, the disruption of which may result in destruction of insulin-secreting cells. The absolute requirement of sublethal irradiation to permit transfer of the disease to non-diabetic adult syngeneic mice provides indirect evidence for the presence of regulatory T cells in non-diabetic NOD mice. We have previously reported that the reconstitution of irradiated recipients by CD4+ T cells from nondiabetic female NOD mice blocks the transfer of diabetes by spleen cells from diabetic donors. We now report evidence that anti-CD4 monoclonal antibodies can substitute for irradiation in rendering adult NOD male mice susceptible to diabetes transfer by diabetogenic spleen cells. Efficient diabetes transfer can be achieved in non-irradiated adult NOD recipients provided they are thymectomized and CD4+ T-cell depleted prior to the transfer. The role of thymectomy is to limit T cell regeneration after anti-T cell monoclonal antibody challenge. Our data confirm that regulatory CD4+ T-cells, which efficiently counterbalance diabetogenic cells, are present in adult NOD male animals.

Regulatory interactions between CD45RBhigh and CD45RBlow CD4+ T cells are important for the balance between protective and pathogenic cell-mediated immunity

BALB/c mice infected with the intracellular protozoan Leishmania major mount a T helper cell 2 (Th2) response that fails to control growth of the parasite and results in the development of visceral leishmaniasis. Separation of CD4+ T cells into CD45RBhigh and CD45RBlow subsets showed that the L. major-specific Th2 cells were contained within the CD45RBlow population as these cells produced high levels of antigen-specific interleukin 4 (IL-4) in vitro and transferred a nonhealing response to L. major-infected C.B-17 scid mice. In contrast, the CD45RBhighCD4+ population contained L. major-reactive cells that produced interferon gamma (IFN-gamma) in vitro and transferred a healing Th1 response to L. major-infected C.B-17 scid mice. Transfer of the Th1 response by the CD45RBhigh population was inhibited by the CD45RBlow population by a mechanism that was dependent on IL-4. These data indicate that L. major-specific Th1 cells do develop in BALB/c mice, but their functional expression is actively inhibited by production of IL-4 by Th2 cells. In this response, the suppressed Th1 cells can be phenotypically distinguished from the suppressive Th2 cells by the level of expression of CD45RB. Although the CD45RBhigh population mediated a protective response to L. major, C.B-17 scid mice restored with this population developed a severe inflammatory response in the colon that was independent of L. major infection, and was prevented by cotransfer of the CD45RBlow population. The colitis appeared to be due to a dysregulated Th1 response as anti-IFN-gamma, but not anti-IL-4, prevented it. Taken together, the data show that the CD4+ T cell population identified by high level expression of the CD45RB antigen contains cells that mediate both protective and pathogenic Th1 responses and that the reciprocal CD45RBlow population can suppress both of these responses. Whether suppression of cell-mediated immunity is beneficial or not depends on the nature of the stimulus, being deleterious during L. major infection but crucial for control of potentially pathogenic inflammatory responses developing in the gut.

Dominant determinants in hen eggwhite lysozyme correspond to the cryptic determinants within its self-homologue, mouse lysozyme: implications in shaping of the T cell repertoire and autoimmunity

We have studied the mouse lysozyme (ML) peptide-specific T cell repertoire in mice of five different major histocompatibility complex (MHC) class II haplotypes. 14 ML peptides were tested in a lymph node T cell proliferation assay. Upon immunization of diverse mouse strains with native ML, there was no response to any of the ML peptides tested. However, nine peptides were immunogenic, although there was no consistent pattern of reactivity toward any peptide among these strains. Thus, an autoreactive T cell repertoire directed against cryptic self(ML)-determinants exists, and it is different in mice of different MHC haplotypes. Moreover, our results demonstrate that crypticity is MHC associated and not merely a structural attribute of the determinant. On comparison of the pattern of response of various peptides of ML and that of its foreign homologue, hen eggwhite lysozyme (HEL) in H-2k, H-2b, and H-2d strains of mice, a striking correlation was evident. The stretches of amino acid sequences of determinants within HEL that were dominant in each of these three strains, almost exactly overlapped in position with those of the cryptic ML determinants against which self-reactivity was demonstrated in the same strain. These results demonstrate that the dominance-crypticity relationship between HEL and ML resulting from differential processing of these two proteins is critical in determining the response to HEL rather than the degree of sequence difference between them. These observations have important implications in the shaping of the T cell repertoire for foreign proteins and in the pathogenesis of autoimmunity.

T-cell subsets in autoimmunity

Although differential cytokine production has been best characterized in CD4+ T cells, it is becoming clear that CD8+ T cells may also be heterogeneous at the level of cytokine production, and that this determines whether they exhibit inflammatory- or suppressor-type properties. Compelling evidence has accumulated in the past few years that cytokines such as interleukin-4, interleukin-10 and transforming growth factor-beta may serve as regulators of cell-mediated immunopathologies by inhibiting the development or effector function of inflammatory T cells that produce cytokines such as interferon-gamma or lymphotoxin.

T-cell autoimmunity in type 1 diabetes mellitus

Insulin dependent diabetes mellitus is a T-cell mediated autoimmune disease. Several beta-cell antigens, mostly non-tissue-specific, have been implicated in the disease process. The antigens and the autoimmune T cells exist in healthy individuals, as do many of the genes required for the development of diabetes. The question, then, is why and how exposure to undefined environmental agents activates an existing autoimmune potential and directs it to damage the beta cells.

Failure of a protective major histocompatibility complex class II molecule to delete autoreactive T cells in autoimmune diabetes

The association of major histocompatibility complex genes with autoimmune diseases is firmly established, but the mechanisms by which these genes confer resistance or susceptibility remain controversial. The controversy extends to the nonobese diabetic (NOD) mouse that develops disease similar to human insulin-dependent diabetes mellitus. The transgenic incorporation of certain class II major histocompatibility complex genes protects NOD mice from diabetes, and clonal deletion or functional silencing of autoreactive T cells has been proposed as the mechanism by which these molecules provide protection. We show that neither thymic deletion nor anergy of autoreactive T cells occurs in NOD mice transgenic for I-Ak. Autoreactive T cells are present, functional, and can transfer diabetes to appropriate NOD-recipient mice.

Monoclonal antibodies for the induction of transplantation tolerance

Non-lytic antibodies to CD4 and certain other T cell adhesion receptors can guide the immune system to become tolerant to foreign antigens, and to regain tolerance in autoimmunity. Tolerance is maintained lifelong through the action of regulatory T cells that in turn can influence naive T cells to acquire the same regulatory properties. A fuller understanding of the molecular basis of infectious tolerance could lead to the design of better immunosuppressive protocols.

Infection of peripancreatic lymph nodes but not islets precedes Kilham rat virus-induced diabetes in BB/Wor rats

A parvovirus serologically identified as Kilham rat virus (KRV) reproducibly induces acute type I diabetes in diabetes-resistant BB/Wor rats. The tissue tropism of KRV was investigated by in situ hybridization with a digoxigenin-labelled plasmid DNA probe containing approximately 1.6 kb of the genome of the UMass isolate of KRV. Partial sequencing of the KRV probe revealed high levels of homology to the sequence of minute virus of mice (89%) and to the sequence of H1 (99%), a parvovirus capable of infecting rats and humans. Of the 444 bases sequenced, 440 were shared by H1. KRV mRNA and DNA were readily detected in lymphoid tissues 5 days postinfection but were seldom seen in the pancreas. High levels of viral nucleic acids were observed in the thymus, spleen, and peripancreatic and cervical lymph nodes. The low levels of infection observed in the pancreas involved essentially only endothelial and interstitial cells. Beta cells of the pancreas were not infected with KRV. These findings suggest that widespread infection of peripancreatic and other lymphoid tissues but not pancreatic beta cells by KRV triggers autoimmune diabetes by perturbing the immune system of genetically predisposed BB/Wor rats.

Following a diabetogenic T cell from genesis through pathogenesis

Nonobese diabetic (NOD) mice spontaneously develop a disease very similar to type 1 diabetes in humans. We have generated a transgenic mouse strain carrying the rearranged T cell receptor genes from a diabetogenic T cell clone derived from a NOD mouse. Self-reactive T cells expressing the transgene-encoded specificity are not tolerized in these animals, resulting in rampant insulitis and eventually diabetes. Features of the disease process emphasize two so-called check-points, recognized previously in the NOD and human diseases but easily misinterpreted. Although NOD mice are protected from insulitis and diabetes by expression of the E molecule encoded in the major histocompatibility complex, the transgenics are not, permitting us to exclude some possible mechanisms of protection.

Interleukin 4 reverses T cell proliferative unresponsiveness and prevents the onset of diabetes in nonobese diabetic mice

Beginning at the time of insulitis (7 wk of age), CD4+ and CD8+ mature thymocytes from nonobese diabetic (NOD) mice exhibit a proliferative unresponsiveness in vitro after T cell receptor (TCR) crosslinking. This unresponsiveness does not result from either insulitis or thymic involution and is long lasting, i.e., persists until diabetes onset (24 wk of age). We previously proposed that it represents a form of thymic T cell anergy that predisposes to diabetes onset. This hypothesis was tested in the present study by further investigating the mechanism responsible for NOD thymic T cell proliferative unresponsiveness and determining whether reversal of this unresponsiveness protects NOD mice from diabetes. Interleukin 4 (IL-4) secretion by thymocytes from > 7-wk-old NOD mice was virtually undetectable after treatment with either anti-TCR alpha/beta, anti-CD3, or Concanavalin A (Con A) compared with those by thymocytes from age- and sex-matched control BALB/c mice stimulated under identical conditions. NOD thymocytes stimulated by anti-TCR alpha/beta or anti-CD3 secreted less IL-2 than did similarly activated BALB/c thymocytes. However, since equivalent levels of IL-3 were secreted by Con A-activated NOD and BALB/c thymocytes, the unresponsiveness of NOD thymic T cells does not appear to be dependent on reduced IL-2 secretion. The surface density and dissociation constant of the high affinity IL-2 receptor of Con A-activated thymocytes from both strains are also similar. The patterns of unresponsiveness and lymphokine secretion seen in anti-TCR/CD3-activated NOD thymic T cells were also observed in activated NOD peripheral spleen T cells. Exogenous recombinant (r)IL-2 only partially reverses NOD thymocyte proliferative unresponsiveness to anti-CD3, and this is mediated by the inability of IL-2 to stimulate a complete IL-4 secretion response. In contrast, exogenous IL-4 reverses the unresponsiveness of both NOD thymic and peripheral T cells completely, and this is associated with the complete restoration of an IL-2 secretion response. Furthermore, the in vivo administration of rIL-4 to prediabetic NOD mice protects them from diabetes. Thus, the ability of rIL-4 to reverse completely the NOD thymic and peripheral T cell proliferative defect in vitro and protect against diabetes in vivo provides further support for a causal relationship between this T cell proliferative unresponsiveness and susceptibility to diabetes in NOD mice.

The use of monoclonal antibodies to achieve immunological tolerance

Monoclonal antibodies are potentially useful immunosuppressive agents. Short courses of CD4/CD8 monoclonal antibody can be used to guide the immune system of experimental animals to accept organ grafts and to arrest autoimmunity. This reprogramming is accompanied by potent T-cell dependent, 'infectious' regulatory mechanisms. A goal for therapeutic immunosuppression should be to understand and harness these innate immunoregulatory mechanisms.

The use of monoclonal antibodies to achieve immunological tolerance

Monoclonal antibodies are potentially useful immunosuppressive agents. Short course of CD4/CD8 monoclonal antibody can be used to guide the immune system of experimental animals to accept organ grafts and to arrest autoimmunity. This reprogramming, reviewed by Herman Waldmann and Stephen Cobbold, is accompanied by potent T-cell dependent, 'infectious' regulatory mechanisms. A goal for therapeutic immunosuppression should be to understand and harness these innate immunoregulatory mechanisms.

Susceptibility and resistance to cyclosporin A-induced autoimmunity in rats

Lethally irradiated Lewis (LEW) rats, reconstituted with syngeneic bone marrow and next given Cyclosporin A (CyA) for several weeks, develop disease (Cyclosporin A-induced autoimmunity; CyA-AI) after withdrawal of CyA. This disease resembles in terms of dermal changes the acute dermatitis and chronic scleroderma also seen in graft-versus-host disease (GVHD). In this study we report the relative resistance of the Brown Norway (BN) rat strain to the induction of CyA-AI. In contrast to LEW rats, in which CyA-AI was originally described, BN rats showed no acute dermatitis or scleroderma-like skin pathology in spite of comparable changes in the thymus and a maturation arrest of CD4+ T cells. The difference was also demonstrated functionally for whereas in LEW rats delayed-type hypersensitivity (DTH) reactions could not be elicited during CyA-AI, these were within normal limits in BN rats subjected to the same protocol; NK activity on the other hand was unaffected in both strains. The observation that BN rats developed very mild late disease as evidenced by a slight though significant weight loss suggests that the BN strain is susceptible to the disease but that lesser effector cell generation or, alternatively, stronger suppressor cell responses may prevent dermal disease. These observations may contribute to the elucidation of the mechanisms involved in this experimental autoimmune disease.