Characterization of the in vitro murine T-cell proliferative responses to murine and human thyroglobulins in thyroiditis-susceptible and -resistant mice

A Novel Mouse Model of Autoimmune Thyroiditis Induced by Immunization with Adenovirus Containing Full-Length Thyroglobulin cDNA: Implications to Genetic Studies of Thyroid Autoimmunity

Background: Thyroglobulin (TG) is a key autoantigen in autoimmune thyroid diseases (AITD). Several single nucleotide polymorphisms (SNPs) in the TG locus were shown to be strongly associated with disease susceptibility in both humans and mice, and autoimmune response to TG is the earliest event in the development of thyroid autoimmunity in mice. The classical model of experimental autoimmune thyroiditis (EAT) is induced by immunizing mice with TG protein together with an adjuvant to break down immune tolerance. The classical EAT model has limited utility in genetic studies of TG since it does not allow testing the effects of TG sequence variants on the development of autoimmune thyroiditis. In this study, we have immunized CBA-J mice, an EAT-susceptible strain, with an adenovirus vector encoding the full-length human TG (hTG) to generate a model of EAT in which the TG sequence can be manipulated to test AITD-associated TG SNPs. Methods: We immunized CBA-J mice with hTG-expressing adenovirus following the well-recognized experimental autoimmune Graves' disease protocol that also uses an adenovirus vector to deliver the immunogen. Results: After hTG adenovirus immunizations, mice developed higher T cell proliferative and cytokine responses to hTG and TG2098 (a major T cell epitope in AITD) and higher titers of TG and thyroperoxidase autoantibodies compared with mice immunized with control LacZ-expressing adenovirus. The mice, however, did not develop thyroidal lymphocytic infiltration and hypothyroidism. Conclusions: Our data describe a novel murine model of autoimmune thyroiditis that does not require the use of adjuvants to break down tolerance and that will allow investigators to test the effects of hTG variants in the pathoetiology of Hashimoto's thyroiditis.

A novel pathogenic peptide of thyroglobulin (2208-2227) induces autoreactive T-cell and B-cell responses in both high and low responder mouse strains

Experimental autoimmune thyroiditis (EAT) is commonly induced by thyroglobulin (Tg) or Tg peptides in mice genetically susceptible to thyroiditis. In the present study, we investigated the immunogenic and pathogenic potential of a novel 20mer human Tg peptide, p2208 (amino acids 2208-2227), in mouse strains classified as low (LR) or high (HR) responders in EAT. The peptide was selected for its content in overlapping binding motifs for MHC class II products, associated with either resistance (A(b)), or susceptibility (A(s), E(k)) to EAT. We therefore immunized LR BALB/c (H-2(d)) and C57BL/6 (H-2(b)) strains, as well as HR CBA/J (H-2(k)) and SJL/J (H-2(s)) mice with 100 nmol of p2208 in adjuvant and collected their sera, lymph nodes and thyroid glands for further analysis. The p2208 peptide was found to contain B-cell and cryptic T-cell epitope(s) in two of the four strains examined, one LR and one HR. Specifically, it elicited direct EAT in C57BL/6 mice (two of seven mice, infiltration index 1-3), as well as in SJL/J mice (two of six mice, infiltration index 1-2). Such an EAT model could provide insights into the immunoregulatory cascades taking place in resistant hosts.

cDNA immunization of mice with human thyroglobulin generates both humoral and T cell responses: a novel model of thyroid autoimmunity

Thyroglobulin (Tg) represents one of the largest known self-antigens involved in autoimmunity. Numerous studies have implicated it in triggering and perpetuating the autoimmune response in autoimmune thyroid diseases (AITD). Indeed, traditional models of autoimmune thyroid disease, experimental autoimmune thyroiditis (EAT), are generated by immunizing mice with thyroglobulin protein in conjunction with an adjuvant, or by high repeated doses of Tg alone, without adjuvant. These extant models are limited in their experimental flexibility, i.e. the ability to make modifications to the Tg used in immunizations. In this study, we have immunized mice with a plasmid cDNA encoding the full-length human Tg (hTG) protein, in order to generate a model of Hashimoto's thyroiditis which is closer to the human disease and does not require adjuvants to breakdown tolerance. Human thyroglobulin cDNA was injected and subsequently electroporated into skeletal muscle using a square wave generator. Following hTg cDNA immunizations, the mice developed both B and T cell responses to Tg, albeit with no evidence of lymphocytic infiltration of the thyroid. This novel model will afford investigators the means to test various hypotheses which were unavailable with the previous EAT models, specifically the effects of hTg sequence variations on the induction of thyroiditis.

Experimental autoimmune thyroiditis in the mouse

Experimental autoimmune thyroiditis (EAT) in mice is an excellent model for Hashimoto's thyroiditis (HT). It is induced with thyroglobulin (Tg), a known thyroid autoantigen that is common to both mouse and human and for which several conserved, thyroiditogenic epitopes have been identified. This unit describes induction and evaluation of EAT using thyroid histology and in vitro proliferative response assays. An ELISA is presented to detect the level of antibody to mouse thyroglobulin (MTg). To induce EAT, either bacterial lipopolysaccharide (LPS) or supplemented complete Freund's adjuvant (CFA) can be used as adjuvant. A support protocol for preparing MTg is included. The T cell proliferation assay can be used to examine the antigenicity of synthetic peptides derived from MTg or heterologous Tg. EAT can be adoptively transferred utilizing cells that have been expanded in vitro, as described. A protocol is provided for inducing tolerance using deaggregated MTg; induction of tolerance requires larger amounts of MTg but efficiently suppresses EAT development. Also included is a protocol to demonstrate the role of regulatory T cells in mediating tolerance. A protocol to delineate HLA association with HT is illustrated using HLA class II transgenic mice.

Pathogenicity of a human thyroglobulin peptide (2340-2359) in mice with high or low genetic susceptibility to thyroiditis

We have previously identified a 20-mer peptide of human thyroglobulin (hTg), p2340 (aa2340-2359), which induced experimental autoimmune thyroiditis (EAT) in AKR/J (H-2(k)) and HLA-DR3 transgenic mice. In this study, we investigated the thyroiditogenic potential of p2340 in 'high responder' CBA/J (H-2(k)) and SJL/J (H-2(s)) or 'low responder' C57BL/6 (H-2(b)) and BALB/c (H-2(d)) mice. Mice were immunized subcutaneously with 100 nmol of p2340 in complete Freund's adjuvant (CFA) and both the proliferative capacity of their lymph node cells in the presence of p2340 or intact Tg and the production of peptide-specific antibodies were investigated. The p2340 peptide was found to contain B-cell and non-dominant T-cell epitope(s) in all strains tested. Moreover, it elicited EAT in CBA/J (2/6, infiltration index (I.I.) 1) and SJL/J (5/5, I.I. 1-3) mice after direct challenge and in BALB/c (4/7, I.I. 1) and C57BL/6 (1/5, I.I. 1) after adoptive transfer of p2340-primed lymph node cells. P2340 is the first Tg peptide found to be pathogenic in low as well as high responder mouse strains and thus will allow us to investigate mechanisms of EAT induction in a genetically resistant host.

The CD40, CTLA-4, thyroglobulin, TSH receptor, and PTPN22 gene quintet and its contribution to thyroid autoimmunity: back to the future

Autoimmune thyroid diseases (AITD) are common autoimmune diseases, affecting up to 5% of the general population. Thyroid-directed autoimmunity is manifested in two classical autoimmune conditions, Hashimoto's thyroiditis, resulting in hypothyroidism and Graves' disease resulting in hyperthyroidism. Autoimmune thyroid diseases arise due to an interplay between environmental and genetic factors. In the past decade significant progress has been made in our understanding of the genetic contribution to the etiology of AITD. Indeed, several AITD susceptibility genes have been identified. Some of these susceptibility genes are specific to either Graves' disease or Hashimoto's thyroiditis, while others confer susceptibility to both conditions. Both immunoregulatory genes and thyroid specific genes contribute to the pathogenesis of AITD. The time is now ripe to examine the mechanistic basis for the contribution of genetic factors to the etiology of AITD. In this review, we will focus on the contribution of non-MHC II genes.

By-stander activation in autoimmune thyroiditis: Studies on experimental autoimmune thyroiditis in the GFP+ fluorescent mouse

We have taken advantage of GFP+ fluorescent protein (GFP) tagged lymphocytes to examine by-stander activity in experimental autoimmune thyroiditis in the mouse. To generate GFP-positive EAT-susceptible CBA/J mice (H-2k) (GFP-CBA/J mice), we backcrossed CBA/J (H-2k) with heterozygous GFP+ transgenic mice (C57Bl/6; H-2b). I-Ak and GFP expression on peripheral lymphocytes was used to select the resulting progeny up to the N7 generation. Mixed lymphocyte reactions using spleen cells from N7 GFP-CBA/J mice showed negative responses to spleen cells from CBA/J confirming the inbreeding and with marked reactivity to cells from C57BL/6. Immunization with human thyroglobulin (hTg) in GFP-CBA/J mice induced thyroiditis in 50% of the animals and high titers of Tg antibodies in all the animals. In addition, priming of GFP+ spleen cells in vitro with hTg induced a marked proliferative response (mean stimulation index = 24.7), These proliferating spleen cells were then transferred to CBA/J recipients. Fourteen days after transferring 30 x 10(6) Tg-primed GFP+ spleen cells into irradiated (500 rad) normal syngeneic hosts, a GFP+ lymphocytic infiltration was seen within their thyroid glands along with a GFP- lymphocytic infiltration arising from the host. This suggested that the hTg-specific transferred cells had initiated by-stander activation of naive host lymphocytes. This model of bystander cell detection confirmed that such an effect occurs in EAT and adds weight to the importance of this phenomenon in the initiation of autoimmune thyroid disease.

Thyroglobulin as an autoantigen: what can we learn about immunopathogenicity from the correlation of antigenic properties with protein structure?

Autoantibodies against human thyroglobulin are a hallmark of autoimmune thyroid disease in humans, and are often found in normal subjects. Their pathogenic significance is debated. Several B-cell epitope-bearing peptides have been identified in thyroglobulin. They are generally located away from the cysteine-rich regions of tandem sequence repetition. It is possible that our current epitopic map is incomplete because of the difficulty that proteolytic and recombinant approaches have in restituting conformational epitopes based upon proper pairing between numerous cysteinyl residues. Furthermore, the homology of cysteine-rich repeats with a motif occurring in several proteins, endowed with antiprotease activity, suggests that these regions may normally escape processing and presentation to the immune system, and brings attention to the mechanisms, such as oxidative cleavage, by which such cryptic epitopes may be exposed. A number of T-cell epitope-bearing peptides, endowed with thyroiditogenic power in susceptible mice, were also identified. None of them was dominant, as none was able to prime in vivo lymph node cells that would proliferate or transfer autoimmune thyroiditis to syngeneic hosts, upon stimulation with intact thyroglobulin in vitro. More than half of them are located within the acetylcholinesterase-homologous domain of thyroglobulin, and overlap B-cell epitopes associated with autoimmune thyroid disease, while the others are located within cysteine-rich repeats. The immunopathogenic, non-dominant character of these epitopes also favours the view that the development of autoimmune thyroid disease may involve the unmasking of cryptic epitopes, whose exposure may cause the breaking of peripheral tolerance to thyroglobulin. Further research in this direction seems warranted.

Non-MHC driven exacerbation of experimental thyroiditis in the postpartum period

Many human autoimmune diseases, including those of the thyroid gland, are affected by immune changes during pregnancy and the postpartum period. To investigate this influence, we have developed an animal model of pregnancy thyroiditis by using thyroglobulin (Tg)-induced experimental autoimmune thyroiditis (EAT). We now report a study of the post-partum period in mice with EAT. At 5 weeks postpartum, which was 9 weeks after the completion of a Tg immunization regime, the mean thyroiditis grade was significantly increased in the postpartum group from 0.23 to 0.43 (p<0.05) and the thyroiditis Index, which reflected both the frequency and severity of thyroiditis, was similarly increased compared to controls (29.0 vs 9.0). When Tg immunized CBA/J (H-2k) female mice were mated with BALB/c (H-2d) males, there was a similar increase in the severity of thyroiditis in the postpartum period as seen with CBA/J males suggesting that allogeneic factors were not able to further this postpartum exacerbation. Spleen cell IL-4 secretion was enhanced in the postpartum but only in the presence of thyroiditis indicating enhanced activity of Th2 immune responses. There were no differences in IFN-gamma secretion, titers of anti-Tg, CD8+ & CD4+ T cells and T cell chemokine receptor (CCR5, CCR3) expression between non-pregnant control mice with thyroiditis and postpartum thyroiditis. In summary, we found that the severity of EAT during the postpartum was significantly greater than in non-pregnant control mice and was associated with enhanced Th2 immune responses. The allogenicity of the pregnancy had no influence on these findings. The lack of allogenic impact was in contrast to earlier observations in pregnancy itself where an exacerbation of thyroiditis was male strain-dependent and involved primarily Th1 responses. This indicated that the postpartum exacerbation of autoimmune thyroid disease was not a simple response to fetal antigens but secondary to unique postpartum factors.

HLA-DR and HLA-DQ polymorphism in human thyroglobulin-induced autoimmune thyroiditis: DR3 and DQ8 transgenic mice are susceptible

In contrast to H2-based susceptibility to experimental autoimmune thyroiditis (EAT) induced with thyroglobulin (Tg), human leukocyte antigen (HLA) association with Hashimoto's thyroiditis, the human counterpart, is less clear, and determining association is further complicated by DR/DQ linkage disequilibrium. Previously, we addressed the controversial implication of HLA-DR genes by introducing HLA-DRA/DRB1*0301 (DR3) transgene into endogenous class II negative H2Ab(0) mice. EAT induction with either human (h) or mouse (m) Tg demonstrated the permissiveness of DR3 molecules for shared Tg epitopes. Here, we examined the participation of HLA-DQ genes by introducing DQA1*0301/DQB1*0302 (DQ8) transgene into class II negative Ab(0) or class I and II negative beta(2)m((-/-)) Ab(0) mice. About 50% and 80% of HLA-DQ8(+) Ab(0) and beta(2)m(-) Ab(0) mice, respectively, developed moderate EAT after hTg immunization, but only minimal response to mTg. The hTg presentation to hTg-primed cells was blocked by anti-DQ mAb in vitro. By contrast, HLA-DRB1*1502 (DR2) and *0401 (DR4) transgenes contributed little to hTg induction. Similarly, DQA1*0103/DQB1*0601 or DQA1*0103/DQB1*0602 (DQ6) transgenic Ab(0) mice were unresponsive to hTg induction and carried no detectable influence in DQ8/DQ6 double transgenic mice. Thus, both HLA-DR and -DQ polymorphism exists for hTg in autoimmune thyroiditis. The use of defined single or double transgenic mice obviates the complications seen in polygenic human studies.

Intrathyroidal fetal microchimerism in pregnancy and postpartum

To investigate a possible relationship between fetal microchimerism and autoimmune thyroiditis, we looked for the presence of fetal cells in the maternal blood and thyroid gland in murine experimental autoimmune thyroiditis (EAT). We used a quantitative PCR-ELISA for products of the SRY locus on the Y chromosome to detect fetal male cells during pregnancy and the postpartum period with a sensitivity of approximately 1 male cell/10(5) female cells. Within the thyroid glands, 12 of 26 (46%) Tg-immunized pregnant mice were SRY positive (range, 1-1700 cells), whereas, in contrast, few SRY transcripts were detected in control thyroids from nonimmunized pregnant mice (P < 0.05). At 5 wk postpartum, although SRY was still detected in the thyroids of 12 of 40 (30%) Tg-immunized mice, the number of male cells was markedly decreased (range, 1-30), and by 10 wk postpartum SRY had disappeared. Using allogeneic male mice heterozygous for green fluorescent protein expression, green fluorescent fetal cells were detected in the blood and bone marrow of pregnant mice. However, green cells were only found in thyroid glands from Tg-immunized pregnant mice that had green fluorescent protein-transgenic green fetuses and not in control nonimmunized pregnant mice. Cytologically, the fetal cells appeared to be of variable origin. Using antibody-mediated affinity purification of thyroid digests we showed this cell population to include fetal cells of T cell and dendritic cell lineage. Hence, fetal cells of immune origin were shown to accumulate within the thyroid glands of mice with EAT during pregnancy and the early postpartum. These data indicated that the inflamed thyroid gland was capable of accumulating fetal cells, including T cells and dendritic cells. Such active immune cells may have a profound regulatory influence on autoimmune thyroiditis in pregnancy and the postpartum period.

IL-12 prevents tolerance induction with mouse thyroglobulin by priming pathogenic T cells in experimental autoimmune thyroiditis: role of IFN-gamma and the costimulatory molecules CD40l and CD28

Deaggregated mouse thyroglobulin (dMTg) induces tolerance to experimental autoimmune thyroiditis (EAT), a Th1-cell-mediated disease. To test whether IL-12, a potent activator of Th1 cells, can overcome tolerance induction, different doses of IL-12 were given to CBA/J mice during the critical interval of 2--3 days after dMTg administration. After challenge with MTg/LPS, dMTg/IL-12-pretreated mice showed more extensive thyroiditis than immunized controls, but comparable levels of anti-MTg and T cell proliferation. Without challenge, few MTg antibodies were produced. In contrast, pretreatment with dMTg/poly A:U or dMTg/IL-1, two other T cell activators which also interfere with tolerance induction, induced antibodies before challenge, but not more severe thyroiditis. Mice pretreated with IL-12 without dMTg developed thyroiditis comparable to immunized controls, but less severe thyroiditis than dMTg/IL-12-pretreated mice. Clearly, IL-12 not only blocked tolerance induction, but also primed antigen-specific T cells during the tolerogenic period of dMTg pretreatment, resulting in stronger thyroiditis than immunization only. Neither treatment with anti-IFN-gamma nor the use of IFN-gamma knockout mice altered the capacity of IL-12 to prevent tolerance induction. However, both anti-CD28 and anti-CD40L antibodies diminished the priming effect by dMTg/IL-12. The mechanisms of IL-12 action include priming of MTg-specific T cells and the involvement of T cell costimulatory molecules.

Pregnancy and murine thyroiditis: thyroglobulin immunization leads to fetal loss in specific allogeneic pregnancies

Thyroid autoantibodies are risk factors in human pregnancy. To investigate the influence of autoimmune thyroiditis on pregnancy, we have studied the impact of murine experimental autoimmune thyroiditis (EAT) on pregnancy outcome by using thyroglobulin (Tg) immunized CBA/J (H2(k)) female mice. When Tg immunized mice were mated with BALB/c (H2(d)) males, only 57% (47/83) of pregnant mice maintained their conceptions compared with >85% of other strain combinations (P < 0.05). We also found that MHC class II antigens were expressed on placental cells from Tg immunized pregnant mice but not in control normal pregnancies. Furthermore, the frequency and severity of thyroiditis, assessed by histological analyses, was also increased in Tg immunized mice mated with the BALB/c strain compared with syngeneic pregnancies (P < 0.05). In these pregnant mice mated with BALB/c, interleukin-4 secretion by mitogen-stimulated spleen cells was significantly suppressed and interferon-gamma secretion by mixed lymphocyte reactions with BALB/c cells was significantly increased. These data demonstrated enhanced Th1 cell proliferation and fetal loss in CBA/J X BALB/c pregnancies. We concluded, therefore, that pregnancy loss was increased in experimental autoimmune thyroiditis in a manner that was dependent on paternal antigens. These observations have broad implications for understanding the immunology of pregnancy.

Noninvolvement of IL-4 and IL-10 in tolerance induction to experimental autoimmune thyroiditis

The mechanisms of tolerance induced with deaggregated mouse thyroglobulin (dMTg) in experimental autoimmune thyroiditis (EAT) is not yet well defined. As shown previously, the induction and maintenance of tolerance require CD4+ T cells exerting active regulatory function to prevent EAT induction. To examine whether Th2 cells are responsible for resistance we injected anti-IL-4 and anti-IL-10, separately or together, into CBA (H2k) mice at the time of MTg pretreatment to study the role of IL-4 and IL-10 in tolerance induction. Our results show that tolerance can be well established without involving IL-4 or IL-10. To determine whether IL-4 was involved in tolerance induction in another EAT-susceptible strain, IL-4 knockout mice on B10.Q background were similarly pretreated with dMTg and immunized. These IL-4 knockout mice exhibited very good tolerance. The lack of response to EAT induction was not due to IL-4 deficiency, since immunized IL-4 knock-out control mice developed severe EAT. Moreover, resistance was strong in IL-4 knock-out mice also given anti-IL-10. The data in both susceptible strains show that IL-4 and IL-10 play a small role in induced resistance to EAT.

Flexibility of the thyroiditogenic T cell repertoire for murine autoimmune thyroiditis in CD8-deficient (beta2m -/-) and T cell receptor Vbeta(c) congenic mice

In murine experimental autoimmune thyroiditis (EAT), previous studies have revealed a highly adaptable thyroiditogenic T cell repertoire which involves both CD4+ and CD8+ T cells in the susceptible H2k strain. To further test this flexibility, congenic B10.K mice lacking CD8+ T cells (B2m -/-) or harboring 70% T cell receptor (TCR) Vbeta gene deletions (Vbeta(c)) were immunized with mouse thyroglobulin (MTg) and evaluated for EAT 28 days later. All B2m -/- mice developed moderate antibodies to MTg, and thyroidal inflammation was comparable to B10.K mice, averaging 35-40%. Spleen cells (SC) from MTg-immunized mice were then injected into syngeneic recipients after stimulation in vitro with MTg or with conserved, thyroxine (T4)- or thyronine (T0)- containing 12mer peptides, hT4(5), hT0(2553), or hT4(2553), derived from the primary hormonogenic sites at position 5 or 2553 of human Tg. As previously shown in another H2k strain (CBA/J), all three peptides activated MTg-primed SC to transfer EAT in B10.K mice. hT4(5) and hT4(2553) were further tested in B10.K-Vbeta(c) and beta2m- B10.K mice. Both peptides expanded thyroiditogenic T cells in either strain, resulting in severe thyroiditis in syngeneic recipients. That EAT can develop in the absence of CD8+ T cells or in the presence of a severely restricted TCR repertoire underscores the remarkable flexibility of the thyroiditogenic T cell profile in the susceptible k haplotype.

Induction of oral tolerance in human autoimmune thyroid disease

Our laboratory has reported suppression of experimental autoimmune thyroiditis in mice by oral feeding with antigen. Based on these data, we considered it possible that oral feeding of animal thyroglobulin (TG) might induce tolerance to antigen in human autoimmune thyroid disease (AITD). Thirteen patients receiving thyroid hormone replacement with synthetic thyroxine (T4) (five patients with Graves' disease, treated with radioiodine 4 to 11 years ago and eight patients with Hashimoto's thyroiditis) were randomly assigned to a test group (switched to replacement with desiccated thyroid from porcine thyroids) and a control group (maintained on synthetic T4). Humoral and cellular immunologic parameters were evaluated in addition to clinical parameters before and every 3 months after the onset of study for a year. At the onset of study, there was no difference in clinical parameters, or humoral and cellular immunity to thyroid autoantigens, except a finding that one thyroid peroxidase (TPO) peptide (100 approximately 119) appeared to stimulate peripheral blood mononuclear cells (PBMC) during in vitro microproliferation assay more in the test group than control group (p = 0.051 by t test). Additionally, almost all of TPO and thyrotropin receptor extracellular domain (TSHR) peptides were slightly more stimulatory to PBMC from the test group than the control group, although this was not statistically significant. After treatment, all variables were analyzed at each time point between groups (t test), and also were analyzed over time in each group (analysis of variance, ANOVA). Among the clinical parameters, thyrotropin (TSH) levels were unchanged and equal. Total serum T4 levels (p < 0.05 at 6 and 12 months after treatment) and free thyroxine indices (FT4I) (p < 0.05 at all time points after treatment) were lower in the test group than the control group. This is an expected result of treatment with desiccated thyroid. We found no change over time nor any difference between groups at time points for titers of antibodies to thyroid autoantigens, ie, human TG, human TPO, and recombinant human TSHR from Escherichia coli. However, cellular immunity, measured by in vitro microproliferation of PBMC to peptides of TPO or TSHR, showed significant differences between groups. At 12 months, stimulatory indices (SI) of PBMC to six peptides, containing the indicated amino acids (764 approximately 95, 100 approximately 119, 110 approximately 129, 261 approximately 275, 441 approximately 448, 708 approximately 727) of 10 TPO peptides, and one peptide (145 approximately 163) of 14 TSHR peptides were lower in the test group than control group (p < 0.05). SI of PBMC to phytohemagglutinin, purified protein derivative from mycobacteria, and tetanus toxoid were not different between groups nor changed over time in any group. In conclusion, treating patients with AITD with an antigen related to the autoantigen TG did not produce changes in humoral immunity parameters, while cellular immunity to certain peptides were apparently suppressed. While the results are both surprising and intriguing, we need more evidence to justify the use of autoantigen as a form of immunospecific therapy in patients with AITD.

Thyroglobulin peptides of specific primary hormonogenic sites can generate cytotoxic T cells and serve as target autoantigens in experimental autoimmune thyroiditis

Previously we demonstrated that thyroxine (T4)-containing, 12-mer peptides from positions 5 (1-12) and 2553 (2549-2560), as well as thyronine (T0)-substituted 2553 peptide, derived from human (H) thyroglobulin (Tg) are capable of activating T cells that infiltrate the thyroid (thyroiditogenic). In contrast, peptides T4(2567) and T0(2567) (2559-2570) are not. To determine if these thyroiditogenic peptides, T4(5), T4(2553), and T0(2553), activated cytotoxic T cells (Tc) and served as target autoantigens when loaded onto indicator cells (BW5147 lymphoma, H2k), lymph node cells from CBA mice immunized with mouse (M) Tg were cultured in vitro with MTg, HTg, or Tg peptide. After MTg or HTg activation, Tc were detected for both MTg- and HTg-loaded target cells in an 18-h, 51Cr-release assay at an effector:target cell ratio of 50:1. These Tc also killed target cells labeled with T4(5), T4(2553), or T0(2553), but not the control peptide T4(2567). When MTg-primed lymphocytes were cultured with T4(5), T4(2553), or T0(2553), specific Tc were also generated against target cells labeled with the respective peptide. The data suggest that one of the thyroiditogenic properties of these peptides previously shown by adoptive transfer of thyroiditis is related to the generation of Tc. In addition, these conserved autoepitopes of Tg also serve as target antigens for Tc.

Suppression of murine thyroiditis via blockade of the CD40-CD40L interaction

The CD40 ligand (gp39) is transiently expressed on activated CD4+ T cells and mediates cognate helper function by interacting with CD40 on B cells. Increasing evidence suggests, however, critical involvement of gp39 not only in antibody-mediated responses but also in the development of effector T cells. Here, we have investigated the effect of in vivo gp39 blockade on the induction of murine experimental autoimmune thyroiditis (EAT), a T-cell-mediated disease. Over a 5-week period, EAT was induced in SJL mice with thyroglobulin (Tg) and adjuvant. Concomitantly, mice received intraperitoneal (i.p.) injections of MR1, a gp39-specific hamster monoclonal antibody (mAb), at 4-day intervals. Control mice were challenged with Tg but received equivalent doses of hamster immunoglobulin (HIg). It was observed that the control mice developed severe thyroiditis whereas the MR1-treated mice exhibited very low levels of infiltration that were mostly focal in nature. Blockade of gp39 was effective since the Tg-specific IgG titres were low or undetectable in all MR1-treated animals compared with the controls. In addition, upon restimulation with Tg in vitro, lymph node cells (LNC) from Tg-primed, MR1-treated mice proliferated less strongly and secreted significantly lower amounts of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma) than LNC from untreated or HIg-treated controls. These results strongly suggest that in vivo blockade of gp39 suppresses EAT by inhibiting the priming of inflammatory Tg-specific T-helper type 1 cells.

Searching for pathogenic epitopes in thyroglobulin: parameters and caveats

Last year marked the 40th anniversary of the discovery that thyroglobulin (Tg) is a major autoantigen in autoimmune thyroiditis. The Tg molecule presents unique challenges for epitope mapping owing to its large size and extensive iodination. Consequently, pathogenic determinants have only recently been identified. Here, George Carayanniotis and Varada Rao summarize the approaches used to determine pathogenic Tg T-cell epitopes and discuss caveats in this unusual quest.

Contrasting immunopathogenic properties of highly homologous peptides from rat and human thyroglobulin

The current lack of amino acid sequence data for mouse thyroglobulin (Tg) necessitates mapping of pathogenic T-cell epitopes on heterologous Tg in mouse experimental autoimmune thyroiditis (EAT). A prevailing assumption has been that epitopes sharing a high degree of amino acid homology among heterologous Tg are likely to exhibit the same immunopathogenic properties in the same host. In this report, we have examined this concept while working with the 18-mer rat(r)Tg(2695-13) peptide that was previously shown to elicit 'A'-restricted T cells and EAT in SJL mice. A major immunopathogenic T-cell epitope was localized within the 12-mer rTg(2695-06). It was found that the human 12-mer homologue that carries two Ser substitutions at Glu2703 and Thr2704 exhibited contrasting properties: it failed to activate Th1 cells in lymphokine and proliferation assays; it did not cross-react with rTg(2695-06) at the T-cell level; and it induced only focal thyroiditis following adoptive transfer of specific lymph node cells. These data highlight the caveat involved in extrapolating results of pathogenic T-cell epitope mapping across heterologous Tgs, even when such epitopes share a high degree of amino acid homology.

HLA-DRB1 polymorphism determines susceptibility to autoimmune thyroiditis in transgenic mice: definitive association with HLA-DRB1*0301 (DR3) gene

Familial clustering of autoimmune thyroid diseases has led to studies of their association with human major histocompatibility complex (MHC) class II genes. One such gene implicated in Hashimoto's thyroiditis (HT) is HLA-DR3, but the association is weak and is contradicted by other reports. On the other hand, murine experimental autoimmune thyroiditis (EAT), a model for HT, presents a clear linkage with MHC class II. Moreover, it is inducible with thyroglobulin (Tg), the common autoantigen in either species. Immunization of HLA-DRB1* 0301 (DR3) transgenic mice with mouse or human Tg resulted in severe thyroiditis. In contrast, transgenic mice expressing the HLA-DRB1*1502 (DR2) gene were resistant to EAT. Our studies show that HLA-DRB1 polymorphism determines susceptibility to autoimmune thyroiditis and implicate Tg as an important autoantigen.

Depletion of CD4+ and CD8+ cells eliminates immunologic memory of thyroiditogenicity in murine experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT) develops in genetically susceptible mice after immunization with mouse thyroglobulin (MTg), and is mediated by T cells, both CD4+ and CD8+, infiltrating the thyroid. Previous work showed that depletion of CD4+, but not CD8+, cells with rat monoclonal antibodies (mAbs) interfered with EAT induction. To test if concomitant CD4+ cell depletion and immunization led to EAT resistance, mice were reimmunized at an interval of 15 or 43 days after injection of CD4 mAbs. No resistance had been established; disease severity and anti-MTg titers were comparable to mice with primary immunization. Previous work also showed that treatment during advancing EAT with only CD4 mAbs on days 21, 25 led to long-lasting, reduced severity in EAT, whereas administration of CD8 mAbs alone reduced the smaller CD8+ subset only. However, therapy with both mAbs was most efficacious; > 50% of thyroids were purged of all cellular infiltrate after only two doses. Moreover, T cells emerging subsequent to depletion were not retained in the thyroid, despite ongoing antibody production. To test if nondepleting CD4 and CD8 mAbs were similarly effective for therapy, mAbs of the IgG2a isotype were administered during advancing EAT. No effect on thyroidal infiltration was observed, indicating that modulation of the CD4 and CD8 antigen without depletion was insufficient for efficacious therapy. To determine if combined therapy with depleting mAbs reestablished self tolerance, treated mice were reimmunized on days 70, 77, when T cell recovery was nearly complete. Thyroiditis was comparable to controls given primary immunization, despite high antibody levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression in murine experimental autoimmune thyroiditis: in vivo inhibition of CD4+ T cell-mediated resistance by a nondepleting rat CD4 monoclonal antibody

Genetically susceptible mice become resistant to experimental autoimmune thyroiditis (EAT) induction with mouse thyroglobulin (MTg) and lipopolysaccharide after pretreatment with deaggregated MTg (dMTg). Recent work showed this suppression to be mediated by CD4+ suppressor T cells (Ts). To study Ts action in vivo, we used a rat IgG2a monoclonal antibody (mAb), YTS 177.9, which modulates CD4 antigen in vivo without depleting CD4+ cells. Initial studies showed that after two 1-mg doses of mAb 7 days apart, extensive CD4 antigen modulation of peripheral blood leukocytes occurred within 4 days. Mice given CD4 mAb 24 hr before dMTg (2 doses, 7 days apart) were resistant to EAT induction when immunized with MTg and LPS 20 days later. Also, anti-rat IgG2a titers were reduced following challenge with heat-aggregated rat IgG2a compared to controls. Subsequent analysis of serum in CD4 mAb-treated animals revealed that mAb was present in the circulation for 14 days. Moreover, mice given CD4 mAb and dMTg, then challenged after only 10 days, when CD4 mAb was still circulating, developed a significantly higher incidence of thyroid damage than controls. These findings suggest that modulation of CD4 antigen does not interfere with Ts activation, but the presence of CD4 mAb, at the time of autoantigenic challenge, can interfere with tolerance to EAT induction. Thus, the direct relationship between the presence of CD4 mAb and inhibition of EAT suppression implicates a role for CD4 molecules in the mediation of suppression.

Synergism between mouse thyroglobulin- and vaccination-induced suppressor mechanisms in murine experimental autoimmune thyroiditis

Previous studies have shown that genetically susceptible mice can be rendered resistant to the induction of experimental autoimmune thyroiditis (EAT) by pretreatment with deaggregated mouse thyroglobulin (dMTg). This resistance is mediated by CD4+ suppressor T cells (Ts) which suppress the afferent/inductive phase of EAT. Recent work has also shown that resistance to EAT can be achieved by vaccination with irradiated spleen cells previously primed in vivo with MTg and cultured in vitro with MTg (gamma SC). The gamma SC-induced resistance also inhibits the afferent phase of EAT but is mediated by both CD4+ and CD8+ Ts. To determine if dMTg- and gamma SC-induced suppression can cooperate to prevent EAT, we pretreated mice with suboptimal doses of dMTg and gamma SC before challenge with MTg and adjuvant. Mice receiving dMTg or gamma SC only showed suppressed in vitro response to MTg, but the development of thyroid lesions was unaltered. However, mice given one or two subtolerogenic doses of dMTg followed by gamma SC not only showed suppressed in vitro response to MTg, but also little or no thyroiditis, indicating cooperation between these two mechanisms. The cooperation was not reciprocal since reversing the order, giving gamma SC first followed by dMTg, was not effective in suppressing EAT. Thus, suppressor mechanisms activated by pretreatment with dMTg and gamma SC can act synergistically to suppress EAT induction; the two mechanisms may cooperate in vivo to maintain self-tolerance provided that MTg-specific CD4+ Ts are initially activated.

The frequency of LPS-responsive B cells to autologous and heterologous thyroglobulin

The frequency of precursors within the mouse splenic B cell pool, reactive with mouse thyroglobulin (mTg) was estimated using a limiting dilution assay system. The mean frequency was found to be 1/3900 B cells. The results provide a minimal estimate of the frequency of mTg-reactive B cells. The frequency of mTg-reactive B cells was not influenced by the MHC locus, as both high- and low-responder strains showed similar frequencies. While the frequency of B cells reactive to human Tg was found to be similar to that reactive to mTg, only 20% of the mTg-reactive clones also cross-react with human Tg. Similarly, only 30% of huTg reactive clones were found to react with mTg. Therefore, a large proportion of Tg-reactive antibodies are restricted to self-determinants and not determinants to conserved regions of the Tg molecule.

Immunogenetic aspects of human thyroglobulin-reactive T cell lines and hybridomas

The in vitro proliferative response to T cells primed with human thyroglobulin (Tg) was compared in 11 independent haplotypes on B10 background. B10.K and B10.S mice were the most responsive, whereas, with the exception of B10.PL (H-2u), all other B10 congenics were intermediate responders. The two best responders to in vitro challenge with human Tg, of the k and s haplotype, are the same as those showing H-2-linked susceptibility to induction of experimental autoimmune thyroiditis (EAT) with mouse Tg. Since shared epitopes on human and mouse Tgs have been shown to be thyroiditogenic by adoptive transfer studies in CBA (H2k) mice, the findings indicate that shared epitopes may be studied in appropriate (i.e. EAT-susceptible) strains of mice. Therefore, we proceeded to develop methods to produce T-cell lines and hybridomas to human Tg in B10.K and B10.S mice, test their cross-reactivity to heterologous Tgs and their Ia restriction patterns. By using antigen-presenting cells from recombinant strains, we identified restriction elements encoded by the I-A subregion alone and a combinatorial molecule from the I-A/I-E subregions.

Suppression in experimental autoimmune thyroiditis: the role of unique and shared determinants on mouse thyroglobulin in self-tolerance

Previous studies have shown that T cells from mice genetically susceptible to experimental autoimmune thyroiditis (EAT) recognize determinants shared between mouse thyroglobulin (Tg) and heterologous Tgs. Some shared determinants are thyroiditogenic; lymphocytes from mice immunized with mouse Tg (MTg) or human Tg (HTg) and reciprocally restimulated in vitro with either Tg can transfer EAT. Studies on the mechanisms of self-tolerance have shown that pretreatment with soluble MTg suppresses in vitro proliferation to MTg and EAT induction with MTg. To determine the role of share epitopes in maintaining tolerance, mice were pretreated with soluble HTg and immunized with HTg or MTg and adjuvant. Cells from HTg-pretreated. HTg-immunized mice showed suppressed in vitro proliferative response to HTg. Following MTg immunization, the cells showed suppressed in vitro response to MTg. However, in contrast to MTg pretreatment, the subsequent development of EAT in vivo was unaltered in severity following HTg pretreatment. Thus, determinants shared between HTg and MTg can induce suppression of in vitro responses to HTg and MTg, but not inhibit the onset of thyroiditis, suggesting that T cells recognizing MTg-unique epitopes expanded to mediate thyroiditis. We conclude that recognition of both unique epitopes expanded to mediate thyroiditis. We conclude that recognition of both unique and shared epitopes on MTg are essential for the overall maintenance of self-tolerance.

Experimental murine thyroiditis induced by porcine thyroid peroxidase and its transfer by the antigen-specific T cell line

Thyroid peroxidase purified from porcine thyroid (pTPO) was found to induce an experimental murine thyroiditis with genetic restriction which was very different from that induced by mouse thyroglobulin (mTg). C57BL/6 and C57BL/10 (both H-2b) were good responders for thyroiditis, whereas A/J (H-2a), BALB/c (H-2d), DBA/2 (H-2d), CBA (H-2k), C3H/He (H-2k), and SJL/J (H-2s) were poor responders. Genetic analyses using congenic or recombinant strains revealed the following results: The H-2-linked gene (probably the I-A subregion) had a weak association with the induction of thyroiditis, and at least one non-H-2-linked gene controlled the development of thyroid lesions; antibody production to pTPO, porcine thyroglobulin (pTg) and mTg did not correlate with the incidence of thyroiditis in any strain. None of the murine thyroid microsome-specific antibodies tested by the indirect immunofluorescent technique was detected. The T cell line specific for pTPO was successfully transferred to produce thyroid lesions in C57BL/6 mice. Thyroiditis appeared 3 days after the transfer of T cell blasts, and a low concentration of anti-pTPO antibodies was detected concurrently. Thyroid lesions remained up to 48 days with almost the same extent of thyroiditis, but anti-pTPO antibodies gradually increased. In the vaccination experiments using either 0.645 C/kg (2500 rad)-irradiated or 0.3% glutaraldehyde-fixed T cell blasts, the induction of thyroid lesions by transfer was strongly suppressed. Glutaraldehyde fixation was more effective than X-irradiation in preventing thyroiditis after the transfer of T cell blasts. Vaccination also suppressed significantly the development of thyroid lesions after pTPO administration.

In situ analysis of T cell subset composition in experimental autoimmune thyroiditis after adoptive transfer of activated spleen cells

T cells from genetically susceptible mice developing experimental autoimmune thyroiditis (EAT) proliferate in response to restimulation with mouse thyroglobulin (MTg) in vitro. The in vitro-activated cells adoptively transfer EAT as well as differentiate into cells cytotoxic for syngeneic thyroid monolayers. To examine the kinetics of T cell subset infiltration and distribution in situ after adoptive transfer, we applied the avidin-biotin-peroxidase labeling technique to thyroid sections, utilizing rat monoclonal antibodies followed by a biotinylated rabbit anti-rat antibody. Female CBA donor mice were immunized with MTg and lipopolysaccharide. Their spleen cells were obtained 7 days later, cultured with MTg, and transferred into recipient mice. The thyroids were removed on Days 7, 10, and 14 after transfer and serially sectioned. The early phase of transferred EAT showed a higher percentage of L3T4+ cells compared to Lyt-2+ cells, yielding a ratio of 2.3 and total T cells of about 35%. By Day 10, both T cell subsets had increased to a total of about 56%. However, the relative increase was greater in the Lyt-2+ subset; the nearly doubled percentage was statistically significant, resulting in a downward shift in the subset ratio to 1.7. Little change in the in situ distribution was seen on Day 14. The percentages of F4/80+ (macrophage) population in lesions examined on Days 10 and 14 were fairly constant and B cell involvement was minimal. These findings illustrate the pathogenic role of both T cell subsets in adoptively transferred EAT and the time-dependent changes in their relative proportions leading to thyroid gland destruction.

Depletion of L3T4+ and Lyt-2+ cells by rat monoclonal antibodies alters the development of adoptively transferred experimental autoimmune thyroiditis

To delineate the contribution of L3T4+ and Lyt-2+ cells in the pathogenesis of experimental autoimmune thyroiditis (EAT), synergistic pairs of monoclonal antibodies (mAb) to the T cell subsets were used in conjunction with the adoptive transfer of mouse thyroglobulin (MTg)-activated cells from immunized mice. Initial experiments verified the important role of L3T4+ cells in the transfer of EAT. Subsequent experiments pointed to the relative contribution of both L3T4+ and Lyt-2+ cells, depending on the stage and extent of disease development. Treatment during disease with L3T4, but not Lyt-2, mAb alone significantly reduced thyroiditis. However, in situ analysis of the cellular infiltrate in thyroid sections revealed that, after treatment with mAb, the appropriate subset was eliminated without altering the amount of the other subset in the remaining lesion. In addition, treatment during severe thyroiditis following the transfer of MTg-activated lymph node cells showed that Lyt-2 mAb alone also reduced thyroid infiltration. When the recipients were pretreated with either pair of mAb before transfer, disease development was only moderately affected. We conclude that (i) donor L3T4+ cells are the primary cells responsible for the initial transfer and development of thyroiditis; and (ii) previous in vitro cytotoxicity data, plus current monoclonal antibody treatment of disease and in situ analysis, further implicate a role for Lyt-2+ cells in EAT pathogenesis.

Immunization of experimental animals with dihydrolipoamide acetyltransferase, as a purified recombinant polypeptide, generates mitochondrial antibodies but not primary biliary cirrhosis

The availability of recombinant mitochondrial autoantigens may permit the experimental study of the pathophysiology of primary biliary cirrhosis. Previously, we demonstrated that high-titer antibodies to the 74 kD mitochondrial autoantigen dihydrolipoamide acetyltransferase could be generated when BALB/c mice were immunized with purified recombinant protein. Based on these data, we attempted an 8-month study to induce antibodies and liver dysfunction by immunizing AKR/J, C3H/J and CBA/HeJ mice as well as rats, guinea pigs, rabbits and rhesus monkeys with purified recombinant human dihydrolipoamide acetyltransferase. Antibodies to dihydrolipoamide acetyltransferase were readily induced and detected in all species of experimental animals with species and strain differences in the titer of the responses. Of particular interest, rabbits and guinea pigs produced antibodies which were specifically reactive with the functional site of dihydrolipoamide acetyltransferase, whereas the other strains and species produced antibodies to other epitopes on the molecule. Finally, similar to data on humans with primary biliary cirrhosis, the pyruvate dehydrogenase enzyme pathway was inhibited in the presence of immunized animal sera. These data imply that features other than simply an antibody response to mitochondrial enzymes are required for the development of primary biliary cirrhosis. Further studies will be necessary to determine the mechanisms by which mitochondrial proteins elicit an immune response.

The initiation and early development of autoimmune diseases

Our understanding of autoimmunity has changed considerably over the past years as a consequence of the demonstration that self-reactive B cells and T cells are not necessarily deleted from the immunological vocabulary. The critical event in initiating (or avoiding) autoimmune responses is presentation to T cells of the self-peptide-MHC antigen complex. Based on the premise that quantitative aspects are of paramount importance, we suggest that T-cell activity, MHC expression, and self-peptide binding determine the initiation of autoimmune responses.

Autoimmune thyroid disease: immunological, pathological, and clinical aspects

Autoimmune thyroiditis, most notably Hashimoto's thyroiditis, appears to be increasing in prevalence and is now more easily detected by sensitive laboratory tests and more invasive procedures such as fine needle aspiration. During the last decade, marked progress has been made in the understanding of these diseases. There is a greater awareness of the interaction between the humoral and cell-mediated arms of the immune system in autoimmune thyroiditis. Recent studies implicate a subpopulation of suppressor T lymphocytes which have an antigen-specific defect, resulting in their suboptimal interaction with the helper T lymphocytes and subsequent autoimmune manifestations. There is some evidence that thyroid epithelial cells which inappropriately express HLA-DR may enhance presentation of thyroid antigens to the immune system, possibly significant in the initiation or enhancement of the autoimmune response. The presence of various antithyroid autoantibodies allows the use of laboratory assays to confirm the clinical diagnosis and predict the results of treatment. There appears to be predisposing genetic factors in the development of autoimmune thyroiditis, with some geographical and racial differences. Environmental factors, most notably dietary intake of iodine, have also been implicated in the pathogenesis of Hashimoto's thyroiditis. Several animal models have been developed addressing such issues. Ongoing studies in the areas of postpartum thyroiditis and childhood thyroiditis are helpful in clarifying their relationship with Hashimoto's thyroiditis. Graves' disease and postpartum thyroiditis are being investigated as possible causes of postpartum depression. The association of Hashimoto's thyroiditis and carcinoma of the thyroid gland is still controversial, but its relationship with malignant lymphoma is now well accepted. Thus, although the pathogenesis of autoimmune thyroiditis remains elusive, there has been significant refinement of the clinical diagnosis, and immunological abnormalities of specific intrathyroidal lymphocytes have been identified. Hopefully, these new areas of knowledge will assist in the treatment of these diseases and in the prevention of the development of malignant lymphomas of the thyroid gland.

The cellular basis for the Ia restriction in murine experimental autoimmune thyroiditis

Susceptibility to experimental autoimmune thyroiditis (EAT) in the mouse is linked to the I-A subregion of the major histocompatibility complex. EAT can be induced in susceptible strains of mice by immunization with mouse thyroglobulin (MTg) and adjuvant. We have described a cell transfer system wherein spleen cells from EAT-susceptible CBA/J mice primed in vivo with MTg and lipopolysaccharide (LPS) can be activated in vitro with MTg to transfer EAT to naive syngeneic recipients. This cell transfer system was used to elucidate the cellular basis for the I-A restriction in EAT. While the cell active in transferring EAT was Thy 1+ I-A-, depletion of I-A+ cells from the in vitro culture prevented the activation of EAT effector T cells. MTg-pulsed mitomycin C-treated naive syngeneic spleen cells as antigen-presenting cells (APCs) could replace the I-A+ cells in vitro. Allogeneic (Balb/c) APCs were ineffective. Using APCs from several recombinant inbred strains of mice, it was shown that C3H/HEN and B10.A(4R) APCs were effective in activating MTg/LPS-primed CBA/J spleen cells to transfer EAT while B10.A(5R) APCs were ineffective. This maps the H-2 restriction to the K or I-A subregions. Addition of polyclonal anti-Iak or monoclonal anti-I-Ak or anti-L3T4 during in vitro activation inhibited both the generation of EAT effector cells and the proliferative response to MTg. Irrelevant anti-Ia reagents, monoclonal anti-I-Ek, and monoclonal anti-I-Jk were ineffective. Thus the I-A restriction in murine EAT appears to result from an I-A restricted interaction between Ia+ APCs and Ia- EAT effector T cells.

Inhibition of experimental autoimmune thyroiditis in mice by anti-I-A antibodies

Experimental autoimmune thyroiditis is induced in mice by immunization with thyroglobulin emulsified in Freund's complete adjuvant. The disease is characterized both by thyroid infiltration with mononuclear cells and by circulating thyroglobulin antibodies. The magnitude of the thyroid infiltration and the titer of thyroglobulin antibodies are controlled by genes in the I-A subregion of the major histocompatibility complex (H-2). We investigated the in vivo effect of monoclonal anti-Ia antibodies on experimental autoimmune thyroiditis in susceptible mice. Antibodies were given around the time of immunization, later after immunization, and to mice with established disease. Monoclonal antibody produced by the hybridoma line 10-3.6 (anti-I-Ak, s, u, v, z, f) completely prevented both production of thyroglobulin antibodies and thyroid infiltrates, when given shortly before or at the time of antigen administration. This effect was dose-dependent and this monoclonal antibody decreased the severity of the disease when given after the antigen challenge but did not fully suppress established thyroiditis. The same antibody markedly decreased the number of B lymphocytes in the spleen and decreased the thyroglobulin-induced spleen cell proliferation when either given in vivo or added in vitro to cell cultures. Antibodies produced by the hybridoma line 11.2.12 (anti-I-Ak) did not show an inhibitory effect on the disease. These experiments suggest that in this model of murine thyroiditis anti-Ia antibodies act on antigen-presenting cells. Furthermore, only one monoclonal antibody, anti-Ia, suppressed the immune response to thyroglobulin, suggesting a possible role for the isotype and specificity of anti-Ia antibody.

Resistance to experimental autoimmune thyroiditis induced by physiologic manipulation of thyroglobulin level

The role of circulatory mouse thyroglobulin (MTg) level in activating mechanisms suppressive to induction of experimental autoimmune thyroiditis (EAT) was studied by two regimens to strengthen normal maintenance of self-tolerance in genetically susceptible mice. One was to administer graded doses of exogenous MTg either 7 days apart or daily for 10 days and then challenge the animals with MTg + LPS. The other was to infuse TSH via an osmotic pump for 7 days. The steady TSH infusion for 7 days resulted in an increase in MTg level peaking on Day 3. Such kinetics of MTg concentration in response to TSH coincided with enhanced resistance to EAT induction. After an initial rapid clearance rate of t1/2 of 3 hr, tolerogenic doses of exogenous MTg sustained similar levels for 2-3 days. In contrast, subtolerogenic doses declined to baseline levels in 2 days or less. Clearance can be best explained by a two-compartment model for distribution with an initial alpha phase (t1/2 about 3 hr), followed by a beta phase (t1/2 about 10 hr). We conclude that, for the prevention of EAT induction in the presence of potent adjuvants (CFA or LPS), a threshold, but above baseline, level of either exogenous or endogenous MTg, represented by the beta phase, is required for a critical period (greater than 2-3 days) to activate suppressor mechanisms over and above homeostatic regulation. Whether MTg concentration raised by TSH (TRH) administration activates suppressor T cells as observed after the injection of a tolerogenic dose of MTg remains to be determined.

Effects of the adjuvants SGP and Quil A on the induction of experimental autoimmune thyroiditis in mice

In the present study, two adjuvants, SGP and Quil A, were assessed for their ability to induce experimental autoimmune thyroiditis (EAT) in mice. SGP (a synthetic copolymer of starch, acrylamide, and sodium acrylate) and Quil A (a plant saponin) were compared with lipopolysaccharide (LPS) and complete Freund's adjuvant (CFA) given together with mouse thyroglobulin (MTg) for their ability to induce EAT in CBA/J mice. Immunization with MTg and LPS, MTg and CFA, or MTg with SGP was effective in inducing anti-MTg antibodies and histologic EAT, while MTg with Quil A was ineffective in inducing either anti-MTg antibodies or EAT. MTg with LPS was able to prime mice for the development of an in vitro spleen cell proliferative response to MTg while MTg with SGP or with Quil A was unable to prime spleen cells to proliferate detectably in response to MTg. MTg with LPS given in vivo primes CBA/J spleen cells for further activation by in vitro culture with MTg to transfer EAT to naive CBA/J recipients. MTg with SGP was also effective in priming CBA/J spleen cells for in vitro activation and transfer of EAT while MTg with Quil A was ineffective. The effective adjuvant activity of SGP and its lack of toxicity relative to LPS should make it a useful agent for further studies in murine models of EAT.

The role of cellular proliferation in the induction of experimental autoimmune thyroiditis (EAT) in mice

Experimental autoimmune thyroiditis (EAT) can be induced in susceptible strains of mice by injection of mouse thyroglobulin (MTg) and adjuvant. Lymphocytes from immunized mice develop a proliferative response to MTg which generally correlates with the development of EAT. We utilize a cell transfer system wherein spleen cells from CBA/J mice primed with MTg and lipopolysaccharide (LPS) in vivo are activated by culture with MTg in vitro to transfer EAT to naive recipients. In vivo priming of CBA/J mice is required to develop an antigen specific proliferative response to MTg. This response is optimal between 48 and 90 hr of culture at an MTg concentration of 125-250 micrograms/ml. The correlation between proliferation and transfer of EAT is not absolute as primed Balb/c X CBA/J F1 and AKR lymphocytes do not proliferate detectably in response to MTg but can be activated to transfer EAT; primed Balb/c lymphocytes neither proliferate nor transfer EAT. Proliferation per se is not sufficient to activate cells to transfer EAT as culture with nonspecific mitogens is not effective in activating primed CBA/J spleen cells to transfer EAT. However, lymphoblasts generated during in vitro culture of primed CBA/J spleen cells with MTg are responsible for transfer of EAT; small lymphocytes are ineffective. We conclude that antigen specific proliferation in response to MTg is essential in activating lymphocytes in vitro to transfer EAT.

Activation of cytotoxic T cells and effector cells in experimental autoimmune thyroiditis by shared determinants of mouse and human thyroglobulins

Previous studies have shown that T cells from genetically susceptible mice developing experimental autoimmune thyroiditis (EAT) proliferate in response to restimulation with mouse thyroglobulin (MTg) in vitro and differentiate into cells cytotoxic for syngeneic thyroid monolayers. To examine further the effector cells involved in pathogenesis and the determinants on MTg responsible for their activation, spleen cells (SC) and lymph node cells (LNC) from mice immunized with MTg or human (H) Tg, and adjuvant (complete Freund's adjuvant (CFA) or lipopolysaccharide (LPS] were cultured in vitro with MTg or HTg. Control cultures were incubated with concanavalin A (Con A) or purified protein derivative (PPD). The in vitro-activated cells which proliferated in response to MTg, HTg, or Con A adoptively transferred thyroiditis to normal recipients, whereas cells transferred directly without in vitro culture were very ineffective. The capacity to transfer EAT was abrogated by irradiation (1500 R), and SC from CFA-immunized control mice which responded in vitro to PPD stimulation did not transfer thyroiditis. The serum titers of MTg autoantibodies were uniformly low and were not correlated with severity of disease. The localization of EAT-effector (precursor) cells depended upon the site of immunization; they were found in the spleens after inguinal (subcutaneous) or systemic (intravenous) immunizations, but were present in the popliteal lymph nodes after hind footpad injections. Both homologous MTg and heterologous HTg functioned as in vivo sensitizing antigen and in vitro activating antigen for each other; such cultured cells transferred thyroiditis in vivo and became cytotoxic for thyroid monolayers in vitro. These findings show that shared determinants are autoantigenic and thyroiditogenic, and support the hypothesis that EAT-effector cells responsible for initiating thyroid damage include cytotoxic cells.