HLA-D/DR expression on epithelial cells: the finger on the trigger?

Naked DNA in cells: An inducer of major histocompatibility complex molecules to evoke autoimmune responses?

The major histocompatibility complex (MHC) is the exclusive chaperone that presents intracellular antigens, either self or foreign to T cells. Interestingly, aberrant expression of MHC molecules has been reported in various autoimmune target tissues such as thyroid follicular cells in Grave’s disease. Herein, we review the discovery of an unexpected effect of cytosolic double-stranded DNA (dsDNA), despite its origins, to induce antigen processing and presenting genes, including MHC molecules, in non-immune cells. Moreover, we highlight several recent studies that suggest cell injury endows thyroid epithelial cells with a phenotype of mature antigen presenting cells by inducing multiple antigen processing and presenting genes via releasing genomic DNA fragments into the cytosol. We discuss the possibility that such cytosolic dsDNA, in naked form without binding to histone proteins, might be involved in the development of cell damage-triggered autoimmune responses. We also discuss the possible molecular mechanism by which cytosolic dsDNA can induce MHC molecules. It is reasonable to speculate that cytosolic dsDNA-induced MHC class I is partially due to an autocrine/paracrine effect of type I interferon (IFN). While the mechanism of cytosolic dsDNA-induced MHC class II expression appears, at least partially, distinct from that mediated by IFN-γ. Further in-depth are required to clarify this picture.

Graves' disease: a host defense mechanism gone awry

In this report we summarize evidence to support a model for the development of Graves' disease. The model suggests that Graves' disease is initiated by an insult to the thyrocyte in an individual with a normal immune system. The insult, infectious or otherwise, causes double strand DNA or RNA to enter the cytoplasm of the cell. This causes abnormal expression of major histocompatibility (MHC) class I as a dominant feature, but also aberrant expression of MHC class II, as well as changes in genes or gene products needed for the thyrocyte to become an antigen presenting cell (APC). These include increased expression of proteasome processing proteins (LMP2), transporters of antigen peptides (TAP), invariant chain (Ii), HLA-DM, and the co-stimulatory molecule, B7, as well as STAT and NF-kappaB activation. A critical factor in these changes is the loss of normal negative regulation of MHC class I, class II, and thyrotropin receptor (TSHR) gene expression, which is necessary to maintain self-tolerance during the normal changes in gene expression involved in hormonally-increased growth and function of the cell. Self-tolerance to the TSHR is maintained in normals because there is a population of CD8- cells which normally suppresses a population of CD4+ cells that can interact with the TSHR if thyrocytes become APCs. This is a host self-defense mechanism that we hypothesize leads to autoimmune disease in persons, for example, with a specific viral infection, a genetic predisposition, or even, possibly, a TSHR polymorphism. The model is suggested to be important to explain the development of other autoimmune diseases including systemic lupus or diabetes.

A novel mouse model of Graves' disease: implications for a role of aberrant MHC class II expression in its pathogenesis

Mice immunized with fibroblasts expressing an MHC class II molecule and human thyrotropin receptor (TSHR), but not either alone, develop major features characteristic of Graves' disease (GD), such as thyroid-stimulating autoantibodies directed against TSHR, increased serum thyroid hormone levels, and enlarged thyroid glands. The results indicate the need for the simultaneous expression of a class II molecule and the TSHR on the surface of the fibroblasts to develop stimulating anti-TSHR antibodies and full-blown GD in our model. A T cell line established from a mouse with hyperthyroidism proliferates in response to fibroblasts expressing a class II molecule and TSHR, but not to the fibroblasts expressing only TSHR, indicating that the class II molecules on the fibroblasts present TSHR-derived peptide(s) to T cells. These results strongly suggest that the acquisition of antigen-presenting ability by thyrocytes can lead to the induction or progression of GD. We identified a T cell epitope of TSHR by the proliferative response of spleen cells from mice immunized with fibroblasts expressing a class II molecule and TSHR to 80 overlapping peptides spanning the extracellular domain of human TSHR. The identification of a major T cell epitope provides an important clue to a novel therapy of GD.

Transforming growth factor-beta1 down-regulation of major histocompatibility complex class I in thyrocytes: coordinate regulation of two separate elements by thyroid-specific as well as ubiquitous transcription factors

Transforming growth factor (TGF)-beta1-decreased major histocompatibility complex (MHC) class I gene expression in thyrocytes is transcriptional; it involves trans factors and cis elements important for hormone- as well as iodide-regulated thyroid growth and function. Thus, in rat FRTL-5 thyrocytes, TGF-beta1 regulates two elements within -203 bp of the transcription start site of the MHC class I 5'-flanking region: Enhancer A, -180 to -170 bp, and a downstream regulatory element (DRE), -127 to -90 bp, that contains a cAMP response element (CRE)-like sequence. TGF-beta1 reduces the interaction of a NF-kappaB p50/fra-2 heterodimer (MOD-1) with Enhancer A while increasing its interaction with a NF-kappaB p50/p65 heterodimer. Both reduced MOD-1 and increased p50/p65 suppresses class I expression. Decreased MOD-1 and increased p50/p65 have been separately associated with the ability of autoregulatory (high) concentrations of iodide to suppress thyrocyte growth and function, as well as MHC class I expression. TGF-beta1 has two effects on the downstream regulatory element (DRE). It increases DRE binding of a ubiquitously expressed Y-box protein, termed TSEP-1 (TSHR suppressor element binding protein-1) in rat thyroid cells; TSEP-1 has been shown separately to be an important suppressor of the TSH receptor (TSHR) in addition to MHC class I and class II expression. It also decreases the binding of a thyroid-specific trans factor, thyroid transcription factor-1 (TTF-1), to the DRE, reflecting the ability of TGF-beta1 to decrease TTF-1 RNA levels. TGF-beta1-decreased TTF-1 expression accounts in part for TGF-beta1-decreased thyroid growth and function, since decreased TTF-1 has been shown to decrease thyroglobulin, thyroperoxidase, sodium iodide symporter, and TSHR gene expression, coincident with decreased MHC class I. Finally, we show that TGF-beta1 increases c-jun RNA levels and induces the formation of new complexes involving c-jun, fra-2, ATF-1, and c-fos, which react with Enhancer A and the DRE. TGF-beta1 effects on c-jun may be a pivotal fulcrum in the hitherto unrecognized coordinate regulation of Enhancer A and the DRE.

Activation of target-tissue immune-recognition molecules by double-stranded polynucleotides

Abnormal expression of major histocompatibility complex (MHC) class I and class II in various tissues is associated with autoimmune disease. Autoimmune responses can be triggered by viral infections or tissue injuries. We show that the ability of a virus or a tissue injury to increase MHC gene expression is duplicated by any fragment of double-stranded (ds) DNA or dsRNA introduced into the cytoplasm of nonimmune cells. Activation is sequence-independent, is induced by ds polynucleotides as small as 25 bp in length, and is not duplicated by single-stranded polynucleotides. In addition to causing abnormal MHC expression, the ds nucleic acids increase the expression of genes necessary for antigen processing and presentation: proteasome proteins (e.g., LMP2), transporters of antigen peptides; invariant chain, HLA-DM, and the costimulatory molecule B7.1. The mechanism is different from and additive to that of gamma-interferon (gammaIFN), i.e., ds polynucleotides increase class I much more than class II, whereas gammaIFN increases class II more than class I. The ds nucleic acids also induce or activate Stat1, Stat3, mitogen-activated protein kinase, NF-kappaB, the class II transactivator, RFX5, and the IFN regulatory factor 1 differently from gammaIFN. CpG residues are not responsible for this effect, and the action of the ds polynucleotides could be shown in a variety of cell types in addition to thyrocytes. We suggest that this phenomenon is a plausible mechanism that might explain how viral infection of tissues or tissue injury triggers autoimmune disease; it is potentially relevant to host immune responses induced during gene therapy.

Thyrocyte class I and class II upregulation is a secondary phenomenon and does not contribute to the pathogenesis of autoimmune thyroid disease

It has been proposed elsewhere that thyrocyte (TEC) class I expression plays a central role in the pathogenesis of autoimmune thyroid disease (AITD). We have studied thyroid xenografts from patients with Graves' disease (GD) and normal (paranodular) (N) tissues in nude and severe combined immunodeficient (SCID) mice. TEC class I and II expression are markedly increased in GD, as compared with N thyroids. When these tissues are transplanted to nude mice in which the immune environment is deleted from the thyroid grafts, TEC class I and class II expression decline to low levels; interferon-gamma (IFN-gamma) but not interferon-alpha (IFN-alpha) will then upregulate TEC class I and class II expression in these N and GD nude xenografts. In SCID mouse xenografts, GD tissue shows higher TEC class I and II expression compared with N. In these SCID mice, both IFN-alpha and IFN-gamma will stimulate TEC class I and II expression further in both GD and N. However, only IFN-alpha increases thyroid antibody (TAb) production from GD SCID grafts, whereas IFN-gamma causes a rise in GD TEC class I and II expression, but no significant increase in TAb. Moreover, in N SCID grafts, despite a rise in TEC class I and II expression induced by both IFNs, no TAb could be detected. Because an immune environment is necessary for TEC class I and II upregulated expression, we conclude that such upregulation is a secondary phenomenon. Because there was dissociation between the stimulation of TEC class I and II expression versus the production of TAb, then at least under these experimental conditions, there is no support for a role for TEC class I and class II upregulation in the pathogenesis of AITD.

Hypotheses on the role of cytokines in peptic ulcer disease

Helicobacter pylori is the cause of chronic type B gastritis and occurs in almost all patients with duodenal ulcers. Infection with H. pylori is characterized by an increased production of several inflammatory cytokines. Increasing evidence suggests a central role of these cytokines in the pathogenesis of H. pylori-associated gastritis and peptic ulcer disease. Cytokines may be crucial in the recruitment and activation of inflammatory cells and in stimulation of gastrin release. In addition to their proinflammatory properties, cytokines may also inhibit the ulcer occurrence by stimulation of prostaglandins and somatostatin release and by direct impairment of acid secretion. The balance of these factors may determine the clinical outcome of H. pylori infection.

Regulation of major histocompatibility class II gene expression in FRTL-5 thyrocytes: opposite effects of interferon and methimazole

Aberrant expression of major histocompatibility complex (MHC) class II antigens is associated with autoimmune thyroid disease; aberrant expression duplicating the autoimmune state can be induced by interferon-gamma (IFNgamma). We have studied IFNgamma-induced human leukocyte antigen (HLA)-DR alpha gene expression in rat FRTL-5 thyroid cells to identify the elements and factors important for aberrant expression. Using an HLA-DR alpha 5'-flanking region construct from -176 to +45 bp coupled to the chloramphenicol acetyltransferase reporter gene, we show that there is no basal class II gene expression in FRTL-5 thyroid cells, that IFNgamma can induce expression, and, as is the case for antigen-presenting cells from the immune system, that IFNgamma-induced expression requires several highly conserved elements on the 5'-flanking region, which, from 5' to 3', are the S, X1, X2, and Y boxes. Methimazole (MMI), a drug used to treat patients with Graves' disease and experimental thyroiditis in rats or mice, can suppress the IFNgamma-induced increase in HLA-DR alpha gene expression as a function of time and concentration; MMI simultaneously decreases IFNgamma-induced endogenous antigen presentation by the cell. Using gel shift assays and the HLA-DR alpha 5'-flanking region from -176 or -137 to +45 bp as radiolabeled probes, we observed the formation of a major protein-DNA complex with extracts from FRTL-5 cells untreated with IFNgamma, termed the basal or constitutive complex, and formation of an additional complex with a slightly faster mobility in extracts from cells treated with IFNgamma. MMI treatment of cells prevents IFNgamma from increasing the formation of this faster migrating complex. Formation of both complexes is specific, as evidenced in competition studies with unlabeled fragments between -137 and -38 bp from the start of transcription; nevertheless, they can be distinguished in such studies. Thus, high concentrations of double stranded oligonucleotides containing the sequence of the Y box, but not S, X1, or X2 box sequences, can prevent formation of the IFNgamma-increased faster migrating complex, but not the basal complex. Both complexes involve multiple proteins and can be distinguished by differences in their protein composition. Thus, using specific antisera, we show that two cAMP response element-binding proteins, activating transcription factor-1 and/or -2, are dominant proteins in the upper or basal complex. The upper or basal complex also includes c-Fos, Fra-2, Ets-2, and Oct-1. A dominant protein that distinguishes the IFNgamma-increased lower complex is CREB-binding protein (CBP), a coactivator of cAMP response element-binding proteins. We, therefore, show that aberrant expression of MHC class II in thyrocytes, induced by IFNgamma, is associated with the induction or increased formation of a novel protein-DNA complex and that its formation as well as aberrant class II expression are suppressed by MMI, a drug used to treat human and experimental autoimmune thyroid disease. Its component proteins differ from those in a major, basal, or constitutive protein-DNA complex formed with the class II 5'-flanking region in cells that are not treated with IFNgamma and that do not express the class II gene.

Iodide suppression of major histocompatibility class I gene expression in thyroid cells involves enhancer A and the transcription factor NF-kappa B

High concentrations of iodide can induce transient, clinical improvement in patients with autoimmune Graves' disease. Previous work has related this iodide action to the autoregulatory effect of iodide on the growth and function of the thyroid; more recently, we additionally related this to the ability of iodide to suppress major histocompatibility (MHC) class I RNA levels and antigen expression on thyrocytes. In this report, we describe a transcriptional mechanism involved in iodide suppression of class I gene expression, which is potentially relevant to the autoregulatory action of iodide. Transfection experiments in FRTL-5 cells show that iodide decreases class I promoter activity and that this effect can be ascribed to the ability of iodide to modulate the formation of two specific protein/DNA complexes with enhancer A, -180 to -170 bp, of the class 1 5'-flanking region. Thus, iodide decreases the formation of Mod-1, an enhancer A complex involving the p50 subunit of NF-kappa B and a c-fos family member, fra-2, which was previously shown to be important in the suppression of class I levels by hydrocortisone. Unlike hydrocortisone, iodide also increases the formation of a complex with enhancer A, which we show, in antibody shift experiments, is a heterodimer of the p50 and p65 subunits of NF-kappa B. The changes in these complexes are not duplicated by chloride and are related to the action of iodide on class I RNA levels by the following observations. First, FRTL-5 thyroid cells with an aged phenotype coincidentally lose the ability of iodide to decrease MHC class I RNA levels and to induce changes in either complex. Second, the effect of iodide on class I RNA levels and on enhancer A complex formation with Mod-1 and the p50/p65 heterodimer is inhibited by agents that block the inositol phosphate, Ca++, phospholipase A2, arachidonate signal transduction pathway: acetylsalicylate, indomethacin, and 5,8,11,14-eicosatetraynoic acid. Interestingly, iodide can also decrease formation of the Mod-1 complex and increase formation of the complex with the p50/p65 subunits of NF-kappa B when the NF-kappa B enhancer sequence from the Ig kappa light chain, rather than enhancer A, is used as probe; and both actions mimic the action of a phorbol ester. This suggests that iodide may regulate complex formation with NF-kappa B regulatory elements on multiple genes associated with growth and function, providing a potential mechanism relating the autoregulatory action of iodide on thyroid cells and its action on class I gene expression.

Major histocompatibility class II HLA-DR alpha gene expression in thyrocytes: counter regulation by the class II transactivator and the thyroid Y box protein

Aberrant expression of major histocompatibility complex (MHC) class II proteins on thyrocytes, which is associated with autoimmune thyroid disease, is mimicked by gamma-interferon (gamma-IFN). To define elements and factors that regulate class II gene expression in thyrocytes and that might be involved in aberrant expression, we have studied gamma-IFN-induced HLA-DR alpha gene expression in rat FRTL-5 thyroid cells. The present report shows that class II expression in FRTL-5 thyrocytes is positively regulated by the class II transactivator (CIITA), and that CIITA mimics the action of gamma-IFN. Thus, as is the case for gamma-IFN, several distinct and highly conserved elements on the 5'-flanking region of the HLA-DR alpha gene, the S, X1, X2, and Y boxes between -137 to -65 bp, are required for class II gene expression induced by pCIITA transfection in FRTL-5 thyroid cells. CIITA and gamma-IFN do not cause additive increases in HLA-DR alpha gene expression in FRTL-5 cells, consistent with the possibility that CIITA is an intermediate factor in the gamma-IFN pathway to increased class II gene expression. Additionally, gamma-IFN treatment of FRTL-5 cells induces an endogenous CIITA transcript; pCIITA transfection mimics the ability of gamma-IFN treatment of FRTL-5 thyroid cells to increase the formation of a specific and novel protein/DNA complex containing CBP, a coactivator of CRE binding proteins important for cAMP-induced gene expression; and the action of both gamma-IFN and CIITA to increase class II gene expression and increase complex formation is reduced by cotransfection of a thyroid Y box protein, which suppresses MHC class I gene expression in FRTL-5 thyroid cells and is a homolog of human YB-1, which suppresses MHC class II expression in human glioma cells. We conclude that CIITA and TSH receptor suppressor element binding protein-1 are components of the gamma-IFN-regulated transduction system which, respectively, increase or decrease class II gene expression in thyrocytes and may, therefore, be involved in aberrant class II expression associated with autoimmune thyroid disease.

Patients treated with interferon-alpha, interferon-beta, and interleukin-2 have a different thyroid autoantibody pattern than patients suffering from endogenous autoimmune thyroid disease

Cytokines are believed to mediate the induction and perpetuation of autoimmune thyroid disease (ATD) in humans. However, this concept is mainly based on in vitro findings and to date, concrete in vivo evidence is still lacking. This prompted us to compare serum thyroid parameters of patients treated with cytokines with patients suffering from ATD. The cytokine group (n = 61) consisted of patients suffering from chronic hepatitis (n = 27) and from hemato-oncological diseases (n = 34). Patients were treated with interferon-alpha (IFN-alpha) or IFN-beta, either alone (n = 31) or in combination with interleukin-2 (IL-2) (n = 15) or with antineoplastic agents (n = 15). The ATD group (n = 105) consisted of 51 patients with Graves' disease, 26 with euthyroid ATD, 18 with Hashimoto's disease, and 10 with atrophic thyroiditis. Only 6 of 61 patients (10%) from the cytokine-treated group had thyroid peroxidase antibody (TPOAb) titers equal to or greater than 100 U/mL, whereas 82 of 87 patients (94%) suffering from ATD had TPOAb titers equal to or greater than 100 U/mL (p = 0.0001). In contrast, the percentage of patients who had thyroglobulin antibody (TgAb) serum titers equal to or greater than 100 U/mL were identical in both groups: 25 of 61 patients (41%) treated with cytokines versus 40 of 87 patients (46%) suffering from ATD (p = 0.789). Thus, patients with ATD had significantly higher TPOAb titers (p = 0.0001) whereas TgAb titers were not significantly different compared with patients from the cytokine group. The substantial difference in autoantibody response raises the possibility that thyroid abnormalities associated with ATD reflect genetic susceptibility and/or an independent stimulus or incident aside from cytokine dysfunction and that cytokines may play a secondary, rather than primary role in disease expression.

Regulation of major histocompatibility complex class I gene expression in thyroid cells. Role of the cAMP response element-like sequence

The major histocompatibility complex (MHC) class I gene cAMP response element (CRE)-like site, -107 to -100 base pairs, is a critical component of a previously unrecognized silencer, -127 to -90 bp, important for thyrotropin (TSH)/cAMP-mediated repression in thyrocytes. TSH/cAMP induced-silencer activity is associated with the formation of novel complexes with the 38-base pair silencer, whose appearance requires the CRE and involves ubiquitous and thyroid-specific proteins as follows: the CRE-binding protein, a Y-box protein termed thyrotropin receptor (TSHR) suppressor element protein-1 (TSEP-1); thyroid transcription factor-1 (TTF-1); and Pax-8. TTF-1 is an enhancer of class I promoter activity; Pax-8 and TSEP-1 are suppressors. TSH/cAMP decreases TTF-1 complex formation with the silencer, thereby decreasing maximal class I expression; TSH/cAMP enhance TSEP-1 and Pax-8 complex formation in association with their repressive actions. Oligonucleotides that bind TSEP-1, not Pax-8, prevent formation of the TSH/cAMP-induced complexes associated with TSH-induced class I suppression, i.e. TSEP-1 appears to be the dominant repressor factor associated with TSH/cAMP-decreased class I activity and formation of the novel complexes. TSEP-1, TTF-1, and/or Pax-8 are involved in TSH/cAMP-induced negative regulation of the TSH receptor gene in thyrocytes, suppression of MHC class II, and up-regulation of thyroglobulin. TSH/cAMP coordinate regulation of common transcription factors may, therefore, be the basis for self-tolerance and the absence of autoimmunity in the face of TSHR-mediated increases in gene products that are important for thyroid growth and function but are able to act as autoantigens.

Induction of Graves-like disease in mice by immunization with fibroblasts transfected with the thyrotropin receptor and a class II molecule

Graves disease is an autoimmune thyroid disease characterized by the presence of antibodies against the thyrotropin receptor (TSHR), which stimulate the thyroid to cause hyperthyroidism and/or goiter. By immunizing mice with fibroblasts transfected with both the human TSHR and a major histocompatibility complex class II molecule, but not by either alone, we have induced immune hyperthyroidism that has the major humoral and histological features of Graves disease: stimulating TSHR antibodies, thyrotropin binding inhibiting immunoglobulins, which are different from the stimulating TSHR antibodies, increased thyroid hormone levels, thyroid enlargement, thyrocyte hypercellularity, and thyrocyte intrusion into the follicular lumen. The results suggest that the aberrant expression of major histocompatibility complex class II molecules on cells that express a native form of the TSHR can result in the induction of functional anti-TSHR antibodies that stimulate the thyroid. They additionally suggest that the acquisition of antigen-presenting ability on a target cell containing the TSHR can activate T and B cells normally present in an animal and induce a disease with the major features of autoimmune Graves.

Hormonal modulation of major histocompatibility complex class I gene expression involves an enhancer A-binding complex consisting of Fra-2 and the p50 subunit of NF-kappa B

Hydrocortisone decreases major histocompatibility complex (MHC) class I gene expression in rat thyroid cells and counteracts increases induced by interferons. Using FRTL-5 cells transfected with class I promoter-reporter gene chimeras, we show that hydrocortisone action is transcriptional and mediated by an element located between 180 and 170 base pairs upstream of the start of transcription. Gel shift assays reveal that hydrocortisone causes the decrease of a specific protein-DNA complex; this same complex, referred to as Mod-1, is increased by interferon. Oligonucleotide competition assays reveal that the Mod-1 complex is associated with enhancer A of the class I gene, -180 to -170 base pairs (5'-GGGGAGTCCCC-3'), immediately upstream of the interferon response element. Antibodies to fra-2, a fos family member, and to the p50, but not the p65, subunit of NF-kappa B supershift the Mod-1 complex. We suggest that hydrocortisone decreases MHC class I gene expression by reducing the formation of Mod-1, which contains both p50 and fra-2; interferon reverses the hydrocortisone effect and increases Mod-1 formation. These observations are relevant to the molecular basis of hydrocortisone therapy in autoimmune thyroid disease and to the actions of interferon to exacerbate or induce autoimmune disease.

Evidence for urothelial cell activation in interstitial cystitis

Bladder biopsy samples from 17 interstitial cystitis patients and 20 controls were evaluated for urothelial cell activation using a panel of monoclonal antibodies to HLA-DR, intercellular adhesion molecule 1, interleukin 1 alpha and tumor necrosis factor alpha. Urothelial cells in the majority (13 of 16, 81%) of the biopsies from patients with interstitial cystitis showed increased expression of HLA-DR, while fewer samples were positive for intercellular adhesion molecule 1 (3 of 16, 19%), interleukin 1 alpha (2 of 17, 12%) or tumor necrosis factor alpha (1 of 15, 7%). No urothelial cell expression of intercellular adhesion molecule 1, interleukin 1 alpha or tumor necrosis factor alpha was detected in the controls, and only 1 of 20 control samples contained HLA-DR positive urothelial cells. These results suggest that an unusual type of cellular activation is present in interstitial cystitis. In vitro studies with cultured normal urothelial cells indicated that cells activated with gamma interferon and tumor necrosis factor alpha expressed intercellular adhesion molecule 1 and HLA-DR, although increases in intercellular adhesion molecule 1 expression occurred earlier. Urothelial cells in interstitial cystitis patients may be defective in ability to express intercellular adhesion molecule 1. Alternatively, the differential expression of HLA-DR and intercellular adhesion molecule 1 in interstitial cystitis specimens may represent a functional subset of interstitial cystitis or reflect different stages of the disease. Urothelial cell activation in interstitial cystitis may result in aberrant immune responses and immune activation within the bladder. Because HLA-DR can be detected in paraffin-embedded tissues, evaluation of urothelial cell HLA-DR expression, although not specific for interstitial cystitis, may become a useful tool in the pathological evaluation of biopsy tissues from patients with this disease.

Epithelial expression of HLA, secretory component (poly-Ig receptor), and adhesion molecules in the human alimentary tract

Epithelial HLA class II is differentially expressed (DR >> DP) only after birth in salivary glands and small intestinal mucosa, in contrast to class I determinants and secretory component (SC) which appear early in gestation. However, there is a brisk postnatal increase in SC expression along with the class II induction, suggesting stimulation by cytokines from activated immune cells. T lymphocytes remain quite scanty in postnatal salivary glands, and the striking SC and class II expression might reflect a synergistic effect of IFN-gamma and TFN-alpha on immature epithelial cells. Enhanced epithelial expression of both SC and class II in salivary glands from sudden infant death victims could be the effect of immunostimulation caused by an infectious agent. Strikingly upregulated SC and epithelial class II expression (DR > DP > DQ) is seen in various inflammatory lesions such as obstructive sialadenitis, Sjögren's syndrome, chronic gastritis, and celiac disease. IFN-gamma and TNF-alpha are most likely involved as the expression patterns can be reproduced with these cytokines in vitro on colonic epithelial cell lines. However, these molecules of the Ig supergene family do not show a selective response in epithelia of inflammatory lesions because increased expression is also seen for lysozyme, lactoferrin and some other proteins. ICAM-1 can be upregulated on epithelial cells by various cytokines in vitro although the situation remains uncertain in mucosal inflammation. The expression pattern in IBD is complicated by dysplastic epithelial changes leading to reduced SC levels which may thus, in turn, jeopardize the poly-Ig transport mechanism. Epithelial class II molecules appear to have antigen-presenting properties, but the immunopathologic role of their increased expression in inflammatory disease in terms of induction of autoimmunity and/or abrogation of oral tolerance is a matter of continuing dispute.

Hormonal regulation of major histocompatibility complex class I genes in rat thyroid FRTL-5 cells: thyroid-stimulating hormone induces a cAMP-mediated decrease in class I expression

Thyrocytes normally express major histocompatibility complex (MHC) class I, but not class II, cell surface antigens. A rat thyrocyte cell line, FRTL-5, also expresses MHC class I antigens, in addition to a variety of thyroid-specific genes. Treatment of FRTL-5 thyrocytes with physiological concentrations of thyroid-stimulating hormone (TSH) has been shown to induce increased expressed of thyroglobulin and thyroid peroxidase but to simultaneously decrease expression of the TSH receptor. The reduction in TSH receptor expression by TSH is cAMP mediated. In the present study, it is demonstrated that, in thyrocytes treated with TSH, MHC class I expression decreases concomitant with the decrease in TSH receptor expression. This decreased expression is evidenced by reduced cell surface levels of MHC class I antigens, by reduced steady-state RNA levels, and by reduced transcription of the class I genes. TSH-mediated reduction of MHC class I gene transcription in FRTL-5 cells was mapped to a region within 135 base pairs of the promoter.

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)

MHC antigen expression in human oral squamous carcinoma cell lines

This study quantified the constitutive and interferon-gamma (IFN-gamma) stimulated expression of MHC class I (HLA-ABC and beta 2 microglobulin) and class II antigens (HLA-DR, -DP, -DQ) on normal and malignant oral keratinocytes using radioimmunoassay and immunocytochemical techniques. Normal keratinocytes and three of four malignant cell lines (H103, H157, H314) expressed MHC class I antigens constitutively; IFN-gamma increased MHC class I expression with significant changes in normals, H157 and H314. Normal keratinocytes expressed significantly more constitutive MHC class I antigens than H103 and H157 and significantly more IFN-gamma stimulated MHC class I antigens than H103, H157 and H314. MHC class II antigens predominantly were not expressed constitutively on normals, H103 and H157 but, in H314, HLA-DR, -DP and -DQ antigens were demonstrated on 35, 11 and 5 per cent of cells, respectively, and resulted in a non-coordinated pattern of expression (HLA-DR greater than -DP = -DQ). IFN-gamma induced HLA-DR on normals, H103 and H157, whilst HLA-DP and -DQ remained undetectable. In H314, IFN-gamma enhanced HLA-DR, -DP and -DQ (significant increase of HLA-DQ) but the interrelationship between these antigens was maintained (HLA-DR greater than -DP = -DQ). Normal keratinocytes expressed significantly more IFN-gamma stimulated HLA-DR than H103 and H157 but significantly less HLA-DR than H314 under similar experimental conditions. One oral malignant cell line (H191) did not express MHC class I and MHC class II antigens either constitutively or in response to IFN-gamma. The results demonstrate aberrant patterns of MHC expression (absence, enhanced, diminished) in the different malignant oral keratinocyte cell lines.

Evidence for accessory cell function by class II MHC antigen-expressing airway epithelial cells

Expression of major histocompatibility complex (MHC) class II antigens is a requirement for accessory cell function in antigen presentation. Recent reports have demonstrated the presence of class II antigens on human bronchial epithelial cells. In the present study, immunohistochemical staining revealed HLA-DR on human airway epithelial cells obtained from two different mucosal sites (lobar bronchus and nasal turbinates). To determine whether airway epithelial cells bear functional class II molecules that allow for their cognate interaction with T lymphocytes, cells isolated from these sites were used in mixed lymphocyte cultures (MLR), as an in vitro model of accessory cell function. Freshly isolated cells (11 bronchi/3 turbinates) stimulated allogeneic T lymphocytes (stimulation index [S.I.] = 9.3 [mean]; P less than 0.001 compared to T cells alone). In order to assess the potential role of contaminating conventional accessory cells, bronchial epithelial cell isolates were first preincubated in a serum-free, growth factor-supplemented medium that functionally eliminates potential non-epithelial stimulators prior to MLR culture. Conventional accessory cell-depleted epithelial cells were still capable of stimulating allogenic T lymphocytes in 18 of 23 MLR cultures (S.I. = 5.5 [mean]; P less than 0.0005 compared to T cells alone). The addition of an anti-class II monoclonal antibody (VG2.2) at the onset of culture completely inhibited the MLR response (n = 10). No shift in the CD4+/CD8+ ratio was detected between lymphocytes harvested from airway epithelial cell MLR (1.42 +/- 1.29) and the ratio from T lymphocytes cultured alone (1.3 +/- 0.75), suggesting that both CD4+ and CD8+ T lymphocytes were proliferating in response to stimulation from alloepitopes recognized on airway epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation between T cell number and epithelial HLA class II expression quantified by image analysis in normal and inflamed human gastric mucosa

Epithelial expression of HLA class II determinants and the number of lamina propria and intraepithelial T cells were quantified in gastric body mucosa by means of paired immunofluorescence staining which was subjected to computerised image analysis. In normal mucosa, epithelial HLA-DR expression was virtually absent. A significantly increased expression was seen in simple chronic gastritis, most extensively in the isthmus zone, where a positive reaction was seen in 34% of the epithelial area when the gastritis was of low degree and in 85% when it was of moderate severity. The most extensive HLA-DR expression was found in moderate 'stump gastritis' 28 to 32 years after Billroth II resections. In these patients the epithelial area in the foveolar and isthmus zones showed 83% and 92% positive responses, respectively. The HLA subregion products were expressed in a differential manner (DR greater than DP greater than DQ). The number of both intraepithelial and lamina propria T cells increased significantly with increasing severity of gastritis, and the fraction of putative memory T cells was also raised. Correlation analyses showed a positive relation between the epithelial expression of HLA-DR and the intraepithelial as well as the lamina propria density of T cell. These results suggest a biological link between T cells, aberrant HLA-DR expression, and gastritis, although the pathogenic importance of this relation is unknown. Enhanced epithelial presentation of autoantigens or luminal antigens, or both leading to increased activation of T cells is one possible explanation.

Class II HLA-DR antigens on non-autoimmune human thyroid cells stimulate autologous T cells with high suppressor activity

Human autoimmune thyroid cells "spontaneously" express MHC-class II antigens. These antigens have been assumed to trigger thyroid-specific helper T cell clones, leading in turn to the expansion of thyroid autoantibody-secreting B cells. Thyroid cells derived from non-autoimmune subjects do not express MHC-class antigens, but these can be readily induced with gamma-interferon. We have addressed the issue of whether it is sufficient for normal thyroid cells to bear class II antigens in order to trigger autologous T cells. We found that non-autoimmune thyrocytes expressing DR antigens fail to stimulate autologous resting T cells. However, proliferative activity and interleukin-2 secretion were observed when fresh T cells were first triggered by autologous non-T cells and then incubated with thyrocytes. More CD8 than CD4 cells proliferated in the T:thyrocyte cultures, but CD4 cells were necessary for the proliferation and interleukin-2 secretion. Addition of antibodies to thyroglobulin or to DR antigens inhibited T cell proliferation and interleukin-2 secretion, thus pointing to T cell recognition of both thyroid-specific and DR antigens. Evaluation of the function of the thyroid stimulated T cells revealed very potent suppressor but negligible helper and cytotoxic activities. It would seem, therefore, that DR-restricted T cell activation by autologous antigen on non-autoimmune thyroid cells does occur, but since it results in enhanced suppression, its nature seems protective, thus leading to maintenance of immunological self-tolerance.

Effects of anti-I-A and anti-I-E monoclonal antibodies on the induction and expression of experimental autoimmune thyroiditis in mice

Susceptibility to experimental autoimmune thyroiditis (EAT) in mice is linked to the I-A subregion of the major histocompatibility complex (MHC). The present study was undertaken to assess the effectiveness of anti-I-Ak monoclonal antibody (MAb) 10-2.16 in preventing or arresting the development of EAT. Spleen cells from CBA/J or (CBA/J x Balb/c) F1 mice given 10-2.16 prior to sensitization with mouse thyroglobulin (MTg) and adjuvant could not transfer EAT to normal recipients, and cells from these mice did not proliferate in vitro to MTg. Donor CBA/J mice given 10-2.16 before immunization and recipients of cells from such mice produced little MTg-specific IgG1 or IgG2b antibody but did produce nearly as much IgG2a as controls. The effects of in vivo treatment with 10-2.16 appear to be due to elimination of Ia + cells rather than to modulation of Ia or induction of suppressor T cells. When 10-2.16 was added to in vitro cultures it also prevented the proliferation and activation of sensitized CBA/J or F1 effector cell precursors. Other mAb specific for MHC class II gene products, but not associated with disease susceptibility, expressed by CBA/J (I-Ek) or F1 (I-Ad) mice (14-4-4S or MK-D6 respectively), also prevented in vivo sensitization, but did not block in vitro activation. Anti-I-Ak was also effective in preventing EAT if multiple injections of mAb were given to recipients of sensitized EAT effector cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Epithelial dendritic cells in pathological human oral tissues

Epithelial dendritic cells (EDC) were examined in human oral tissues with non-specific keratosis, lichen planus and squamous cell carcinoma. Acetone-fixed frozen sections were stained using an indirect immunoperoxidase technique and monoclonal antibodies to the human CD1 thymocyte (OKT6) and HLA-DR antigens. Significantly more T6+ and DR+ EDC were present in lichen planus tissues than normal controls, tissues with non-specific keratosis and the epithelial overlying/adjacent to squamous cell carcinomas, the latter tissues having comparable numbers of both T6+ and DR+ EDC. By contrast, significantly fewer T6+ EDC and significantly more DR+ cells were present in the invasive epithelium of squamous cell carcinomas than the overlying/adjacent epithelium of carcinomas, the non-specific keratosis group and the normal tissues. 23-60% of pathological tissues had either focal or general DR+ reactivity in keratinocytes, but there was no correlation between the density of T6+ or DR+ EDC and the keratinocyte DR status of the tissues. The results suggest that immunological enhancement occurs in lichen planus and possibly immunological impairment may characterize invasive squamous cell carcinoma.

The relationship between epithelial Ia expression and the inflammatory cell infiltrate during experimental oral carcinogenesis

The development of oral epithelial expression of Ia antigens and its relationship to the presence of IL-2r+ (CD25+) cells was investigated in rats treated with the water soluble carcinogen 4-nitroquinoline-N-oxide (4NQO). Acetone fixed frozen sections of the palate and tongue were stained using an indirect immunoperoxidase technique and monoclonal antibodies to rat Ia (I-A & I-E) and IL-2 receptor. After 4 weeks 4NQO treatment all rats expressed oral epithelial Ia but thereafter (2-9 months) expression was present in only 20-40% of animals. Epithelial expression of Ia by histologically normal, dysplastic and neoplastic epithelium was always associated with the presence of an underlying inflammatory cell infiltrate containing CD25+ cells. Overall there were significantly more CD25+ cells in tissue specimens containing Ia+ epithelium compared with Ia- epithelium. Furthermore, during the first 4 weeks of carcinogen treatment, a significant positive correlation was found between the CD25+ cell density and occurrence of focal epithelial Ia expression. These results, together with analysis of the T cell, NK cell, macrophage and B cell content of the infiltrates induced by 4NQO, suggest that the CD25+ cells represent activated T cells. Thus, our results in this experimental model are consistent with the idea that epithelial expression of Ia is the result of production of IFN-gamma by locally activated T cells.