How many genes code for organ-specific autoimmunity?

Circulating cytokines and complements in chronic heart failure

Elevated levels of cytokines and complements have been reported in patients with advanced heart failure, but the exact clinical significance remains unclear. Therefore, assessments correlated with hemodynamic and clinical variables may provide important insight into the actions of cytokines and complements in chronic heart failure. The authors evaluated the clinical significance of cytokines and complements. The study included 60 subjects (50 men, 10 women); 34 had idiopathic dilated cardiomyopathy (DCM) and 26 had ischemic heart disease (IHD). Tumor necrosis factor alpha and interleukin-2 receptor concentrations in chronic heart failure were greater than in control subjects (20.0 +/- 0.4 vs 18.0 +/- 0.5 pg/mL, p<0.05 and 817.23 +/- 63.50 vs 642.75 +/- 27.31 pg/mL, p<0.05, respectively). There was no significant difference between DCM and IHD patients in circulating levels of the cytokines and the components complements (p=NS). Additionally, although functional classes III and IV heart failure patients showed a tendency to increase the levels of the cytokines and the component complements, these differences were not statistically significant (p=NS). Similarly, correlation analysis showed that the levels of the circulating cytokines and the component complements had independent value for mortality. These results suggest that humoral and cellular immunity abnormalities may play an important role in the pathogenesis of heart failure and dilated cardiomyopathy.

Glucocorticoid resistance and the immune function in the immunodeficiency syndrome

Glucocorticoids, the final product of HPA axis, and their receptors (GRs) on mononuclear cells are crucial mediators in the endocrine-immune interaction. An alteration in GRs involving a lower receptor affinity (Kd) for glucocorticoids has been found in a group of advanced AIDS patients, who developed Addisonian symptoms (weakness, weight loss, hypotension, hyponatremia, and intense mucocutaneous melanosis) in spite of hypercortisolism and normal or slightly elevated values of ACTH (AIDS-GR). In these patients, data for the suppression test showed decreased cortisol and ACTH suppression in response to exogenous dexamethasone. The inhibitory effect of dexamethasone on radiolabeled-thymidine incorporation in mononuclear cells from these patients was also reduced. Monocytes of AIDS-GR patients had a receptor Kd of 10.5 +/- 4.2 nmol/l that was higher than that of other AIDS patients (AIDS-C) (2.9 +/- 0.8 nmol/l) and normal subjects (2.0 +/- 0.8 nmol/l: p < 0.01). Correlations were found between plasmatic IFN-alpha and receptor Kd on monocytes of AIDS-GR (r = 0.77). Poly (i)-poly (c)-induced IFN-alpha production by monocytes was inhibited by glucocorticoids in the AIDS-C group and controls (approx. 80% in both groups): The effect was reversed by the receptor antagonist RU-486. By contrast, glucocorticoid did not inhibit IFN-alpha production in AIDS-GR group. In conclusion, levels of plasmatic IFN-alpha, a cytokine with antiviral properties, may be increased several times, and dexamethasone fails to inhibit monocytes' IFN-alpha production only in AIDS with cortisol resistance, a disturbance that confirms an important immunoregulatory role of glucocorticoids in HIV disease.

The thyrotropin receptor

This chapter has outlined the complex process required for thyroid growth and function. Both events are regulated by TSHR via a multiplicity of signals, with the aid of and requirement for a multiplicity of hormones that regulate the TSHR via receptor cross-talk: insulin, IGF-I, adrenergic receptors, and purinergic receptors. Cross-talk appears to regulate G-protein interactions or activities induced by TSH as well as TSHR gene expression. The TSHR structure and its mechanism of signal transduction is being rapidly unraveled in several laboratories, since the recent cloning of the receptor. In addition, the epitopes for autoantibodies against the receptor that can subvert the normal regulated synthesis and secretion of thyroid hormones, causing hyper- or hypofunction, have been defined. Studies of regulation of the TSHR minimal promotor have uncovered a better understanding of the mechanisms by which TSH regulates both growth and function of the thyroid cell. A key novel component of this phenomenon involves TSH AMP positive and negative regulation of the TSHR. Negative transcriptional regulation is a common feature of MHC class I genes in the thyroid. Subversion of negative regulation or too little negative regulation is suggested to result in autoimmune disease. Methimazole and iodide at autoregulatory levels may be important in reversing this process and returning thyroid function to normal. Their action appears to involve factors that react with the IREs on both the TSHR and the TG promoter. Too much negative regulation, as in the case of ras transformation, results in abnormal growth without function. TTF-1 is implicated as a critical autoregulatory component in both positive and negative regulation of the TSHR and appears to be the link between TSH, the TSHR, TSHR-mediated signals, TG and TPO biosynthesis, and thyroid hormone formation. Differentially regulated expression of the TSHR and TG by cAMP and insulin depend on differences in the specificity of the TTF-1 site, that is, the lack of Pax-8 interactions with the TSHR, and the IRE sites. Single-strand binding proteins will become important in determining how TSHR transcription is controlled mechanistically.

Increased circulating cytokines in patients with myocarditis and cardiomyopathy

OBJECTIVES

To elucidate the potential role of cytokines in the pathogenesis of cardiomyopathy and myocarditis.

BACKGROUND

Experimental studies show that certain cytokines depress myocardial contractility and that tumour necrosis factor-alpha plays an important part in the pathogenesis of myocardial injury in animal models of viral and autoimmune myocarditis.

METHODS

Plasma interleukin 1-alpha, interleukin 1-beta, interleukin-2, interleukin-6, tumour necrosis factor-alpha, tumour necrosis factor-beta, granulocyte-macrophage colony stimulating factor, granulocyte colony stimulating factor, macrophage colony stimulating factor, interferon-alpha and interferon-gamma were measured in 13 patients with acute myocarditis, 23 patients with dilated cardiomyopathy, 51 patients with hypertrophic cardiomyopathy, nine patients with acute myocardial infarction, 18 patients with angina pectoris, 12 patients with essential hypertension and 17 healthy controls.

RESULTS

Increased concentrations of cytokines were not detected in the controls. In patients with acute myocarditis, interleukin 1-alpha was detected in 23% (mean (SD) 25 (11) pg/ml), tumour necrosis factor-alpha in 46% (61 (31) pg/ml), and macrophage colony stimulating factor was 2.5 (1.8) ng/ml (normal 1.9 (0.4)). In patients with dilated cardiomyopathy, tumour necrosis factor-alpha was detected in 35% (402 (555) pg/ml). In patients with hypertrophic cardiomyopathy, interleukin-2 was detectable in 14% (2318 (4738) pg/ml) and tumour necrosis factor-alpha ws detected in 20% (992 (1517) pg/ml). The concentration of macrophage colony stimulating factor was raised in patients with acute myocardial infarction. Granulocyte colony stimulating factor was often increased in myocarditis, cardiomyopathies, acute myocardial infarction, and angina pectoris--suggesting activation of macrophages and/or endothelial cells--but this increase was not specific to these diseases. Increased concentrations of cytokines were not found in patients with essential hypertension.

CONCLUSION

These results suggest that cytokines may play a part in the pathogenesis of myocardial injury in myocarditis and cardiomyopathies and that further studies to explore the potential pathogenetic role of cytokines in myocardial diseases may be warranted.

The role of the immunoendocrine interaction via the hypothalamo-pituitary-adrenal axis in autoimmune disease Emphasis on the obese strain chicken model

The key to the molecular basis of the pathogenesis of autoimmune disease (AID) certainly lies in the identification of genes coding for the altered immune response and those responsible for the susceptibility of the target organ to the autoimmune attack. The elucidation of nonessential modulatory factors is, however, also of great importance, because it is via these routes that an effective AID therapy is practical at the present time. Hormones in general, and those affecting the hypothalamo-pituitary-adrenal (HPA) axis in particular, are among the best candidates for more rational new therapeutic approaches. Studies of immune-endocrine communication in animal models with spontaneously occurring organ-specific or systemic autoimmune diseases are ideal for this kind of investigation, since immunologic studies commencing prior to onset of the AID in question can be performed.

Molecular basis for the autoreactivity against thyroid stimulating hormone receptor

The present report identifies an important immunogenic region of the TSH receptor and determinants on the TSH receptor for the two types of autoantibodies seen in hyperthyroid Graves' disease and hypothyroid idiopathic myxedema, TSAbs and TSBAbs, respectively. The immunogenic domain with no important functional determinants, is contained within residues 303-382 and involves residues 352-366 in particular. There are determinants flanking the immunogenic domain on the C-terminal portion of the receptor which are the TSBAb and high affinity TSH binding sites: residues 295-306, 387-395, and tyrosine 385. Determinants on the N-terminal portion of the external domain, centered on residues 38-45, are TSAb interactions linked to low affinity TSH binding important for signal generation: threonine 40 and residues 30-33, 34-37, 42-45, 52-56, and 58-61. These determinants are conserved in human and rat receptors, are not present in gonadotropin receptors, and are each related to separate actions of TSH: binding vs. signal generation. They can, therefore, account for organ specific autoimmunity and the different disease expression effected by TSBAbs vs TSAbs, i.e. hypo- vs. hyperthyroidism, respectively. It is proposed that, in the thyroid, hormonal (TSH, insulin, hydrocortisone, IGF-I) suppression of class I genes might be one means of preserving self-tolerance in the face of the hormone action to increase the expression of tissue specific genes such as thyroglobulin and thyroid peroxidase. Inappropriately high class I expression in the thyroid, i.e. if induced by interferon, viruses, or some as yet unknown agent, would contribute to the generation of autoimmune disease. Thus, it would result in increased antigen presentation to the immune system, particularly those autoantigens increased by TSH and its cAMP signal such as thyroglobulin or thyroid peroxidase, or whose turnover is increased by TSH and its cAMP signal, such as the TSH receptor. In the case of the latter, peptide 352-366, known to be near a protease sensitive site on the receptor [41,49], would now act as a potent self-antigen and induce the formation of receptor autoantibodies. It is further proposed that methimazole and high doses of iodide are therapeutically effective agents in thyroid autoimmune disease because they, in part, decrease MHC class I gene expression. Speculation is presented which suggests that elimination of negative regulation of MHC class I and the TSH receptor is an important factor in the development of autoimmune thyroid disease.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of interleukin 2 in the development of autoimmune thyroiditis

Interleukin 2 (IL-2) is a lymphokine that may disrupt immunological self-tolerance. While being incapable of interfering with intrathymic or peripheral clonal deletion, IL-2 may overcome functional antigen unresponsiveness in anergic T lymphocytes. Anergy of T helper cells of the inflammatory phenotype implies selective silencing of the transcription of the IL-2 gene and thus precludes autocrine IL-2/IL-2 receptor (IL-2R) mediated growth, as well as delivery of help to other T cells or B lymphocytes. Thus, IL-2 serves as a servomodulator regulating post-deletional self-tolerance. IL-2-producing and IL-2-receptive cells are present in a variety of autoimmune lesions, including spontaneous autoimmune thyroiditis developing in the Obese strain (OS) of chickens, in Hashimoto's struma lymphomatosa, and in Graves' disease. Whereas the OS is characterized by a hyperinducibility of the IL-2/IL-2R system that predisposes to the development of severe thyroid infiltration, the state of the IL-2/IL-R system in circulating lymphocytes of patients developing thyroid autoimmunity, or at risk of doing so, remains to be defined. The most frequent autoimmune side-effect of IL-2 treatment concerns the thyroid gland. IL-2 induces a lymphoid thyroiditis leading to primary hypothyroidism, especially in those patients that have pre-treatment antithyroid autoantibodies. The hypothesis is extrapolated that IL-2 induces autoimmune disease in those patients that bear undeleted thyroid-specific T cells, and in which the lack of manifest thyroiditis relies upon peripheral, post-deletional tolerance.

Cytokines and autoimmune disease

A wide array of cytokines are locally present in autoimmune lesions where they are produced by inflammatory cells or by the target cell of the autoimmune attack. The presence of cytokines at the site of autoaggression reflects ongoing inflammatory and activation processes. These mediators exert proinflammatory effects, contribute to the activation and stimulation of the effector function of T or B lymphocytes, directly participate in target cell destruction, and mediate accompanying local reactions, including fibrotic processes. The release of cytokines into the circulation may explain certain systemic reactions, including fever or changes in the profile of plasma proteins. Many, especially systemic, autoimmune diseases are accompanied by a dysregulation of lymphokine secretion at the level of circulating leukocytes or cells situated outside of the local inflammatory event, thus reflecting regulatory disorders that may either have a genetic or an acquired basis. Decreased production of lymphokines in vitro in response to nonspecific stimuli may be accompanied by an elevated spontaneous release in vivo resulting in an increase of circulating cytokine levels (interleukin 2, tumor necrosis factor-alpha). Secretion of interleukin 1, interleukin 2, and tumor necrosis factors-alpha or -beta, in part, is determined by genetic factors and it is possible that a particular secretor phenotype may predispose to the development of autoimmune lesions. Probably due to their pleiotropic nature, systemic administration of cytokines such as interleukin 1, interleukin 2, tumor necrosis factor, and interferon-gamma may exert either accelerating or suppressive effects on autoimmune diseases. Conversely, agents that block the function of the lymphokine interleukin 2 exert an unequivocal autoimmune disease-inhibiting effect.

Analysis of the immune-encodrine feedback loop in the avian system and its alteration in chickens with spontaneous autoimmune thyroiditis

In both mammals and chickens, immunization with exogenous antigens results in a surge of serum glucocorticoid hormone levels concomitant with the antibody response. This effect is mediated by glucocorticoid-increasing factors (GIF) produced by cells of the immune system. In the avian system, GIF appear to act via the hypothalamo-pituitary axis and not directly on the adrenal gland. Interleukin 1 is the main active substance responsible for GIF activity, as shown by molecular sieve and immunoaffinity chromatography studies. In contrast to data from mammals, we found no evidence that interleukin 2 elevates chicken corticosterone. Obese strain chickens with spontaneous Hashimoto-like autoimmune thyroiditis are deficient in their in vivo GIF response. Because no differences were found between autoimmune and healthy chickens in the corticosterone response of the adrenal gland after ACTH administration, and since autoimmune animals are able to react normally to immobilization stress, it is assumed that this deficiency is due to a specific defect rather than a general disturbance in the endocrine system.