A critical role for TRAIL in resolution of granulomatous experimental autoimmune thyroiditis

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin (MTG)-sensitized splenocytes activated in vitro with MTG and IL-12. Thyroid lesions reach maximal severity 20 days after cell transfer, and usually resolve or progress to fibrosis by day 60 depending on the extent of thyroid damage at day 20. Our previous studies indicated that neutralization of TNF-alpha or FasL had no effect on G-EAT induction, but neutralization of TNF-alpha promoted, while neutralization of FasL inhibited, G-EAT resolution. TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily. This study was undertaken to define the role of endogenous TRAIL in G-EAT development and/or resolution. Neutralization of endogenous TRAIL had little effect on G-EAT induction, but significantly inhibited G-EAT resolution and increased thyroid fibrosis. This correlated with higher expression of pro-inflammatory cytokines and preferential expression of the pro-apoptotic molecule TRAIL, and anti-apoptotic molecules FLIP and Bcl-xL on inflammatory cells in thyroids of anti-TRAIL-treated recipients. The results suggest that endogenous TRAIL is not required for G-EAT development in recipients, but is critical for G-EAT resolution. Endogenous TRAIL might promote resolution, at least in part, through modulation of the balance between pro- and anti-inflammatory cytokines, and the expression pattern of pro- and anti-apoptotic molecules of thyroid epithelial cells (TECs) and inflammatory cells.

Role of TGFbeta in development of spontaneous autoimmune thyroiditis in NOD.H-2h4 mice

Nearly 100% of NOD.H-2h4 mice develop spontaneous autoimmune thyroiditis (SAT) and produce anti-mouse thyroglobulin autoantibodies when they receive 0.05% NaI in their drinking water beginning at 8 wk of age. Our previous studies showed that TGFbeta1 mRNA was constitutively expressed in thyroids and spleens of normal NOD.H-2h4 mice but not other strains of mice. To determine whether TGFbeta might have a role in SAT, mice were given anti-TGFbeta mAb at various times during development of SAT. Anti-TGFbeta markedly inhibited development of SAT and production of anti-mouse thyroglobulin IgG1 autoantibodies. Anti-TGFbeta was most effective in inhibiting SAT when given during the time thyroid lesions were developing, i.e., starting 4 wk after administration of NaI water. The active form of the TGFbeta1 protein was present in thyroids of mice with SAT but not in normal NOD.H-2h4 thyroids. However, thyrocytes of normal NOD.H-2h4 thyroids did express latent TGFbeta1. TGFbeta1 protein expression in the thyroid correlated with SAT severity scores, and administration of anti-TGFbeta inhibited TGFbeta1 protein expression in both the thyroid and spleen. TGFbeta1 was produced primarily by inflammatory cells and was primarily localized in areas of the thyroid containing clusters of CD4(+) T and B cells. Depletion of CD8(+) T cells had no effect on TGFbeta1 protein expression. Activation of splenic T cells was apparently not inhibited by anti-TGFbeta, because up-regulation of mRNA for cytokines and other T cell activation markers was similar for control and anti-TGFbeta-treated mice. TGFbeta1 may function by promoting migration to, or retention of, inflammatory cells in the thyroid.

Expression and regulation of Fas and Fas ligand on thyrocytes and infiltrating cells during induction and resolution of granulomatous experimental autoimmune thyroiditis

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by mouse thyroglobulin-sensitized spleen cells activated in vitro with mouse thyroglobulin, anti-IL-2R, and IL-12. G-EAT lesions reach maximal severity 19-21 days after cell transfer, and lesions almost completely resolve by day 35. Depletion of CD8+ cells delays resolution and reduces Fas ligand (FasL) mRNA expression in thyroids. This study was undertaken to analyze Fas and FasL protein expression in the thyroid during induction and resolution of G-EAT and to determine whether CD8+ cells might regulate Fas or FasL expression in the thyroid. Fas and FasL expression was analyzed by immunohistochemical staining or in situ hybridization in thyroids of mice with or without depletion of CD8+ cells. Fas and FasL proteins were not detectable in normal thyroids, but expression of both proteins increased during development of G-EAT. Fas was expressed primarily by inflammatory cells; some enlarged thyrocytes were also Fas+. Thyrocytes had intense FasL immunoreactvity, and many CD8+ cells were also FasL positive. Depletion of CD8+ cells resulted in decreased FasL expression by thyrocytes and inflammatory cells, but had no effect on Fas expression. TUNEL assay detected many apoptotic inflammatory cells in proximity to thyrocytes. CD8-depleted thyroids had ongoing inflammation with fewer apoptotic infiltrating cells at day 35. Administration of a neutralizing anti-FasL mAb had no apparent effects on development of G-EAT, but anti-FasL was as effective as anti-CD8 in preventing G-EAT resolution. These results suggested that CD8+ T cells and thyrocytes may kill inflammatory cells through the Fas pathway, contributing to G-EAT resolution.

Transforming growth factor-beta has contrasting effects in the presence or absence of exogenous interleukin-12 on the in vitro activation of cells that transfer experimental autoimmune thyroiditis

Mouse thyroglobulin (MuTg)-sensitized spleen cells activated in vitro with MuTg induce experimental autoimmune thyroiditis (EAT) in recipient mice with a thyroid infiltrate consisting primarily of lymphocytes. A more severe and histologically distinct granulomatous form of EAT (G-EAT) is induced when donor cells are activated with MuTg together with anti-interferon-gamma (IFN-gamma), anti-interleukin-2 receptor (IL-2R) monoclonal antibody (mAb), and IL-12. Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that can both suppress and exacerbate autoimmune diseases and often has inhibitory effects on lymphocytes. To determine if TGF-beta could modulate the in vitro activation of effector cells for G-EAT, TGF-beta was added to cultures of MuTg-sensitized donor spleen cells together with MuTg. Cells activated in the presence of 2 ng/ml TGF-beta induced moderately severe G-EAT in recipient mice. G-EAT induced by cells activated in the presence of TGF-beta was histologically similar but less severe than the G-EAT induced by cells activated in the presence of IL-12. IL-12 and TGF-beta modulate the activation of G-EAT effector cells by distinct mechanisms, as cells activated by TGF-beta could induce G-EAT in the presence of anti-IL-12, and TGF-beta inhibited the effects of IL-12 on EAT effector cells. TGF-beta exerted its activity during the first 24 h of the 72-h culture, whereas IL-12 functioned primarily during the final 24 h of culture. These results indicate that thyroid lesions with granulomatous histopathology can be induced by both IL-12-dependent and IL-12-independent mechanisms, and TGF-beta can exert both positive and negative effects on the effector cells for G-EAT.

Induction of experimental autoimmune thyroiditis in IL-12-/- mice

Granulomatous experimental autoimmune thyroiditis (G-EAT) is induced by transfer of mouse thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTg and anti-IL-2R or MTg and IL-12. Previous work suggested that IL-12 was required in vitro for development of G-EAT. To determine whether IL-12 was also required during the induction and/or effector phases, DBA/1 mice with a disrupted IL-12-P40 gene (IL-12(-/-)) were used for EAT induction. Cells from MTg-sensitized IL12(-/-) donors activated in vitro by MTg or MTg and anti-IL2R induced severe EAT in recipient mice. Compared with effector cells from IL-12(+/+) donors, effector cells from IL-12(-/-) donors induced thyroid lesions dominated by lymphocytes with minimal granulomatous changes. Thyroids of recipients of IL-12(-/-) cells expressed less IFN-gamma mRNA and more TGF-beta, IL-4, and IL-10 compared with recipients of IL-12(+/+) cells. When IL-12 was added during in vitro activation, cells from both IL-12(-/-) and IL-12(+/+) donors induced severe G-EAT, and expression of all cytokines except IL-12 was comparable in thyroids of both IL-12(+/+) and IL-12(-/-) recipients. Transfer of cells from IL-12(+/+) or IL-12(-/-) donors into IL-12(+/+) or IL-12(-/-) recipients indicated that IL-12 expressed in thyroids was derived from recipients. Thus, endogenous IL-12 is not absolutely essential for the sensitization and activation of EAT effector cells to induce severe EAT, although it is required in vitro to promote activation of cells to induce severe granulomatous histopathology.

Adoptive transfer murine model of granulomatous experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT) is a chronic inflammatory autoimmune disease that can be induced in genetically susceptible animals by immunization with mouse thyroglobulin (MTg) in an appropriate adjuvant or by the adoptive transfer of MTg-sensitized donor spleen cells, activated in vitro with MTg, into naive recipients. In the adoptive transfer model used in our laboratory, donor cells activated with MTg alone induce a relatively mild chronic lymphocytic form of EAT (L-EAT), in which the thyroid infiltrate consists primarily of mononuclear cells, and the thyroid inflammation persists for several months. When the same donor cells are activated with MTg together with anti-IL-2R and/or IL-12, a more severe and histologically distinct granulomatous form of EAT is induced in recipient mice. In addition to having distinct histopathologic features, granulomatous EAT (G-EAT) differs from L-EAT in that granulomatous thyroid lesions are not chronic. After reaching maximal severity 21 days after cell transfer, G-EAT thyroid lesions either resolve or the thyroids become atrophic and fibrotic by day 35. In this review, the histopathologic features of G-EAT and L-EAT are described, and our studies with the adoptive transfer G-EAT model which have focused on the mechanisms involved in induction of G-EAT in mice, and the evolution of G-EAT lesions to resolution of inflammation or fibrosis, are reviewed.

Characteristics of inflammatory cells in spontaneous autoimmune thyroiditis of NOD.H-2h4 mice

Thyroid lesions develop in most NOD.H-2h4 mice 6 weeks after they are given 0.05% NaI in drinking water. B cells are required for spontaneous autoimmune thyroiditis (SAT) development, and anti-thyroglobulin autoantibody levels correlate with SAT severity. Immunohistochemical staining of thyroids obtained 2-10 weeks after administration of NaI water suggested that CD4+ T cells initially infiltrated the thryoid, followed by CD8+ T cells and B cells. Intrathyroidal CD4+ T cells are more numerous than CD8+ T cells. CD4+ T cells and B cells form aggregates in the thyroid, while CD8+ T cells are scattered throughout the thyroid. Intrathyroidal germinal centre-like structures could be observed in thyroid lesions with 2-3+ SAT and intrathyroidal B cells co-expressed OX40L. By RT-PCR, intrathyroidal expression of OX40L, OX40, CD40L, IL-2R, CTLA-4 and Igbeta mRNA correlated closely with the SAT severity score. These molecules were not expressed in normal thyroids. In the spleen, OX40L-positive cells were detected at 2 weeks and increased 4-6 weeks after NaI water. OX40, OX40L, CD40L, IL-2R and B7-1 as well as IFN-gamma and IL-4 mRNA were minimally expressed in normal spleens, usually began to be expressed at 2 weeks and increased to maximal level 4-8 weeks after NaI water. These results suggest that in NOD.H-2h4 mice, the OX40L, OX40, CD40L and B7 molecules, which increase in the spleen and thyroid of these mice after receiving NaI water, may play a role in SAT development, implying that one or more of these molecules might be good targets for the prevention or treatment of SAT.

Early requirement for B cells for development of spontaneous autoimmune thyroiditis in NOD.H-2h4 mice

B cells are known to play an important role in the pathogenesis of several autoimmune diseases. NOD.H-2h4 mice develop spontaneous autoimmune thyroiditis (SAT) and anti-mouse thyroglobulin (MTg) autoantibodies, the levels of which correlate closely with the severity of thyroid lesions. NOD.H-2h4 mice genetically deficient in B cells (NOD.Kmu(null)) or rendered B cell-deficient by treatment from birth with anti-IgM develop minimal SAT. B cells were required some time in the first 4-6 wk after birth, because NOD.Kmu(null) or NOD.H-2h4 mice did not develop SAT when they were reconstituted with B cells as adults. The requirement for B cells was apparently not solely to produce anti-MTg autoantibodies, because passive transfer of anti-MTg Ab did not enable B cell-deficient mice to develop SAT, and mice given B cells as adults produced autoantibodies but did not develop SAT. B cell-deficient mice developed SAT if their T cells developed from bone marrow precursors in the presence of B cells. Because B cells are required early in life and their function cannot be replaced by anti-MTg autoantibodies, B cells may be required for the activation or selection of autoreactive T cells. These autoreactive T cells are apparently unable to respond to Ag if B cells are absent in the first 4-6 wk after birth.

Characterization of thyroid fibrosis in a murine model of granulomatous experimental autoimmune thyroiditis

This study was initiated to identify and characterize thyroid fibrosis in a murine model of granulomatous experimental autoimmune thyroiditis (G-EAT) and determine if TGF-beta1 might be involved in fibrosis. G-EAT was induced by transfer of mouse thyroglobulin-sensitized spleen cells activated in vitro with thyroglobulin, anti-IL-2R, and IL-12. There was almost complete destruction of thyroid follicles, leading to fibrosis of the gland and reduced serum T4 levels. Fibrosis was confirmed by staining for collagen and alpha smooth-muscle actin, a marker of myofibroblasts. Kinetic studies characterized the onset and development of thyroid fibrosis. TGF-1beta was increased at mRNA and protein levels, and expression of TGF-beta1 protein paralleled G-EAT severity. Comparison of staining patterns showed that TGF-beta1 was expressed in areas of myofibroblast and collagen accumulation, implying that TGF-beta1 may play a role in fibrosis in G-EAT. Further studies demonstrated that myofibroblasts, macrophages, and thyrocytes contributed to TGF-beta1 production. This provides an excellent model to study the mechanisms of fibrosis associated with autoimmune damage.

Apoptosis of thyrocytes and effector cells during induction and resolution of granulomatous experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT) with granulomatous histopathology (G-EAT) can be induced by cells from mouse thyroglobulin (MTg)-immunized donors activated in vitro with MTg and IL-12. G-EAT lesions reach maximum severity 18-21 days after cell transfer and, if some thyroid follicles remain, lesions almost completely resolve by day 35. CD8(+) cells are required for G-EAT resolution. To begin to determine the mechanisms involved in G-EAT resolution, apoptosis in thyroids was analyzed by TUNEL staining. Apoptotic thyrocytes and inflammatory cells were present in the thyroids of both CD8(+) and CD8-depleted recipient mice at day 19-21. By day 35, apoptotic cells were rare in thyroids of mice whose lesions had resolved; the few apoptotic inflammatory cells were generally in close proximity to thyroid follicles. Thyroids of CD8-depleted mice had ongoing inflammation at day 35 and most apoptotic cells were thyroid follicular cells. The expression of Fas and Fas ligand (FasL) mRNA in thyroids was also determined by RT-PCR in both CD8(+) and CD8-depleted recipient mice. Fas was expressed in normal thyroids and its expression was relatively constant throughout the course of disease. FasL mRNA was not expressed in normal thyroids. FasL mRNA expression generally correlated with G-EAT severity, being maximal at day 21 and diminishing as lesions resolved. However, FasL mRNA expression in thyroids of CD8-depleted mice in which resolution was delayed was decreased compared to thyroids of CD8(+) mice with comparable disease severity, suggesting that FasL expressed by CD8(+) cells may play a role in G-EAT resolution.

Spontaneous autoimmune thyroiditis in NOD.H-2h4 mice

NOD.H-2h4 mice, which express I-Ak on the NOD genetic background, spontaneously develop autoimmune thyroiditis (SAT) and anti-mouse thyroglobulin (MTg) autoantibodies. The incidence of SAT is nearly 100% in mice of both sexes 6-8 weeks after administration of 0.05% NaI in the drinking water. After reaching maximum severity, inflammation is chronic over the next 3-4 months. All mice that develop thyroid lesions also produce MTg-specific IgG1 and IgG2b autoantibodies. Thyroid lesions and anti-MTg autoantibodies did not develop in CBA/J (H-2(k)) or NOD.SWR(H-2(q)) mice after administration of NaI water. Both CD4(+)and CD8(+)T cells are involved in the initial development of SAT. Depletion of CD4(+), but not CD8(+), T cells after thyroid lesions have developed also markedly reduced SAT severity, indicating that CD4(+)T cells are required for both developing and maintaining SAT. Analysis of cytokine gene expression indicated that both Th1 and Th2 cytokines were expressed in thyroids of NOD.H-2h4 mice with SAT. Th1 and proinflammatory cytokines were maximally expressed 4-6 weeks after mice began receiving NaI water, while Th2 cytokine gene expression was greatest at 8-15 weeks, when lesions had reached maximal severity and were in the chronic phase. TGF-beta was highly expressed in NOD.H-2h4 thyroids, irrespective of whether the mice had received NaI water or had thyroid lesions.

CD40L is necessary for the priming of effector cells for lymphocytic and granulomatous experimental autoimmune thyroiditis

The interaction of CD40 on antigen presenting cells (APC) with CD40L on mouse thyroglobulin (MTg)-specific T cells may deliver an essential signal for the development of CD4(+) experimental autoimmune thyroiditis (EAT) effector cells and anti-MTg producing B cells. To determine the requirement for CD40-CD40L interactions in G-EAT, donor mice were injected with an anti-CD40L monoclonal antibody (mAb) on days -1, 0, and +1 relative to immunization with MTg and adjuvant. Recipients of spleen cells from MTg-primed donor mice injected with anti-CD40L did not develop EAT, while spleen cells from similarly immunized hamster Ig-treated donors transferred severe G-EAT. Although the decreased EAT severity was accompanied by increased IL-4 mRNA expression by CD4(+) T cells from anti-CD40L-treated donors, the increased IL-4 was not necessary for suppression of EAT, since anti-CD40L treatment prevented EAT in IL-4-deficient mice. Addition of MTg-primed B cells during in vitro activation of spleen cells from anti-CD40L-treated donors did not induce EAT in recipients, suggesting that anti-CD40L suppresses EAT by preventing the sensitization of EAT effector cells. Addition of anti-CD40L during in vitro activation of MTg-primed spleen cells or treatment of recipients with anti-CD40L had no effect on EAT severity, indicating that CD40-CD40L interactions are not required after EAT effector cells are primed to MTg.

B7.2 has opposing roles during the activation versus effector stages of experimental autoimmune thyroiditis

APCs provide costimulatory and down-regulatory signals to Ag-activated T cells through interactions between B7.1 and B7.2 on APCs with either CD28 or CTL Ag-4 expressed on T cells. Recipients of mouse thyroglobulin (MTg)-primed spleen cells activated in the presence of anti-B7.2 had decreased experimental autoimmune thyroiditis (EAT) severity compared with recipients of cells cultured with control rat Ig or anti-B7.1. Blocking B7.2 during in vivo priming also suppressed the ability of MTg-primed spleen cells to transfer EAT, implicating a role for B7.2 for priming and in vitro activation of EAT effector cells. In contrast, administration of anti-B7.2 or anti-B7.2 Fab to recipients of MTg-activated spleen cells increased the severity of EAT compared with recipients receiving control Ig. Thyroids from anti-B7.2-treated recipients had increased expression of IL-4 mRNA compared with thyroids from rat Ig-treated controls. Both B7.1 and B7.2 molecules were expressed in the thyroids of mice with EAT, although B7.2 was more prevalent than B7.1. Administration of both anti-B7.1 and anti-B7.2 to recipient mice suppressed the development of EAT, while anti-B7.1 treatment alone had no effect on EAT severity. The suppression of EAT was not observed when anti-B7.1 and anti-B7.2 treatment was delayed until 7 days after cell transfer, suggesting a requirement for B7 in the initiation of EAT in recipient mice. These results suggest that costimulation is required during the effector phase of EAT and that B7.2 may have opposing roles in the activation versus effector stages of autoreactive T cells.

The kinetics of cytokine gene expression in the thyroids of mice developing granulomatous experimental autoimmune thyroiditis

To study the potential roles of cytokines in development and resolution of granulomatous experimental autoimmune thyroiditis (EAT), the kinetics of in vivo expression of cytokine genes in thyroid infiltrates was analysed using reverse transcriptase-PCR (RT-PCR). Both Th1 (IL-2 and IFN-gamma) and Th2 (IL-4 and IL-10) cytokines as well as TGF-betaTNF-alphaIL-12 and IL-1beta were detected in thyroids during both the initial phase and peak of granulomatous EAT. Maximal expression of cytokine genes generally occurred 11-14 days after cell transfer, prior to maximal EAT severity, which occurred 19-21 days after cell transfer. The relative ratios of Th1:Th2 cytokines and mouse thyroglobulin-(MTg)-specific IgG1 and IgG2a autoantibody levels were similar during both the initial phase and peak of EAT. Depletion of CD8(+) T cells did not decrease the severity of EAT but delayed resolution of lesions. Cytokine gene expression in thyroids was not decreased by anti-CD8 treatment. Together, these data indicate that both Th1 and Th2 cytokines produced by CD4(+) T cells are involved in induction and development of granulomatous EAT, and CD8-dependent resolution of granulomatous EAT is apparently not mediated by these cytokines.

IFN-gamma-deficient mice develop severe granulomatous experimental autoimmune thyroiditis with eosinophil infiltration in thyroids

To study the role of IFN-gamma in the development of granulomatous experimental autoimmune thyroiditis (EAT), DBA1 mice with a disrupted IFN-gamma gene were used for adoptive EAT induction. Effector cells from either IFN-gamma(+/+) or IFN-gamma(-/-) donor mice activated with mouse thyroglobulin and anti-IL-2R mAb induced severe granulomatous EAT. A predominant infiltration of the thyroid by eosinophils was observed in recipients of IFN-gamma(-/-) effector cells but not in recipients of IFN-gamma(+/+) cells. Compared with wild-type mice, thyroids of recipients of IFN-gamma(-/-) effector cells had decreased expression of mRNA for Th1 cytokines and inducible nitric oxide synthetase. Expression of Th2 cytokine mRNA was comparable to that of IFN-gamma(+/+) mice, and expression of eotaxin was increased in the thyroids of recipients of IFN-gamma(-/-) effector cells. Activation of cells from either IFN-gamma(+/+) or IFN-gamma(-/-) donors in the presence of IL-12 also induced severe granulomatous EAT. Eosinophil infiltration in recipients of IFN-gamma(-/-) cells was unaffected when effector cells were activated with IL-12, and thyroids expressed predominantly Th2 cytokines. The extent of fibrosis of recipient thyroids was generally greater when donor IFN-gamma(+/+) and IFN-gamma(-/-) cells were activated with IL-12. Compared with IFN-gamma(+/+) mice, IFN-gamma(-/-) mice produced lower levels of mouse thyroglobulin-specific autoantibodies after immunization with MTg and LPS. These results indicate that cells from both IFN-gamma(+/+) and IFN-gamma(-/-) donors can induce severe granulomatous EAT. However, damage of thyroid follicles by IFN-gamma(-/-) and that by IFN-gamma(+/+) cells appear to involve different mediators of inflammation.

Interleukin-12 promotes activation of effector cells that induce a severe destructive granulomatous form of murine experimental autoimmune thyroiditis

Granulomatous inflammatory lesions are a major histopathological feature of a wide spectrum of human infectious and autoimmune diseases. Experimental autoimmune thyroiditis (EAT) with granulomatous histopathological features can be induced by mouse thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTg and anti-interleukin-2 receptor (anti-IL-2R), anti-IL-2, or anti-interferon-gamma (anti-IFN-gamma) monoclonal antibody (MAb). These studies suggested that IFN-gamma-producing T cells requiring IL-2 for growth may negatively regulate activation of granulomatous EAT effector cells. As IL-12 promotes activation of IFN-gamma-producing Th1 cells, the present study was undertaken to determine the role of IL-12 in activation of effector cells for granulomatous EAT. MTg-sensitized cells activated in vitro with MTg, anti-IL2R MAb, and IL-12 induced severe, destructive granulomatous thyroiditis with neutrophil inflammation, fibrin deposition, and necrosis. Many glands ultimately underwent atrophy and became fibrotic; some also showed fibrinoid necrosis and a mixed inflammatory cell infiltration of blood vessel walls indicative of a necrotizing vasculitis. Induction of severe granulomatous EAT by IL-12 required MTg in vitro and was unrelated to the IL-12-induced increase in IFN-gamma production. IL-12 markedly increased IFN-gamma production but did not induce a shift to a Th1-dominant phenotype, as other Th1 and Th2 cytokines were generally unaffected and both Th1 and Th2 cytokines were expressed in recipient thyroids. Addition of IL-12 or neutralization by anti-IL-12 at various times indicated that IL-12 exerted its primary effects in the final 24 hours of the 72-hour culture and was not required in recipient mice. Cells cultured with anti-IL-12, MTg, and anti-IL2R MAb transferred mild lymphocytic EAT but little or no granulomatous EAT. Thus, IL-12 profoundly regulates the in vitro activation of effector cells that induce histologically distinct autoimmune inflammatory lesions in the thyroid.

Induction of granulomatous experimental autoimmune thyroiditis in IL-4 gene-disrupted mice

To study the role of IL-4 in development of granulomatous experimental autoimmune thyroiditis (EAT), IL-4 gene-disrupted mice expressing the EAT-susceptible H-2k haplotype were generated and used for EAT induction. Spleen cells from mouse thyroglobulin (MTg) and LPS-primed IL-4(+/+) and IL-4(-/-) donors could induce severe granulomatous EAT when spleen cells were activated with MTg and anti-IL-2R mAb in the presence of IL-12. Thyroid lesions had extensive follicular cell proliferation, large numbers of histiocytes, polymorphonuclear leukocytes, and multinucleated giant cells, in addition to lymphocytes and other mononuclear cells. Expression of IFN-gamma gene mRNA and production of IFN-gamma by effector spleen cells stimulated with MTg and IL-12 were similar for both IL-4(+/+) and IL-4(-/-) mice. Although IL-4 was undetectable in IL-4(-/-) mice, expression of mRNA for IL-5, IL-10, and IL-13 and production of IL-5 by both MTg-activated spleen cells and anti-CD3-activated CD4+ T cells were comparable for cells from IL-4(+/+) and IL-4(-/-) mice, indicating that the absence of IL-4 did not prevent production of other Th2 cytokines. Production of MTg-specific IgG1 was very low or undetectable in IL-4(-/-) mice. IL-4 gene mRNA and MTg-specific IgG1 could be detected in IL-4(+/+) or IL-4(-/-) recipients only when they received effector cells from IL-4(+/+) donor mice, indicating that IL-4- and IgG1-secreting cells are of donor origin. These results demonstrate that IL-4 is not essential for development of granulomatous EAT.

A thyroxine-containing thyroglobulin peptide induces both lymphocytic and granulomatous forms of experimental autoimmune thyroiditis

Mouse thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTg can induce two histologically distinct forms of experimental autoimmune thyroiditis (EAT). MTg-sensitized cells activated with MTg alone induce a mild chronic form of EAT in which the thyroid infiltrate consists primarily of lymphocytes and other mononuclear cells (lymphocytic EAT). The same donor cells activated with MTg and anti-IL2R mAb induce a more severe and acute form of EAT with a thyroid inflammatory lesion having granulomatous histopathological features. A thyroxine-containing (T4) peptide, corresponding to positions 2549-2560 of human Tg, was shown by others to activate spleen cells of mouse thyroglobulin (MTg)-sensitized CBA/J mice to induce lymphocytic EAT. To determine if the CD4+ effector T cells that induce granulomatous EAT can respond to the same T-cell epitope, the present study was undertaken to determine if both forms of EAT could be induced by the 2549-2560 thyroxine (T4)-containing peptide. This peptide was very effective for activation of T cells from MTg-primed CBA/J donors to induce granulomatous EAT but, in contrast to MTg, did not activate T cells from AKR/J or DBA/1 mice to induce granulomatous EAT. The T4 peptide did not apparently activate peptide-specific B cells in vivo but did activate MTg-primed B cells in vitro to produce anti-MTg autoantibody in recipient mice. These results demonstrate that a single 12-amino-acid thyroxine-containing peptide can activate T cells from CBA/J mice to induce both lymphocytic and granulomatous EAT. However, this peptide does not activate T cells from some other EAT-susceptible strains of mice, suggesting that MTg contains multiple epitopes able to activate T cells to induce granulomatous EAT.

Intravenous administration of deaggregated mouse thyroglobulin suppresses induction of experimental autoimmune thyroiditis and expression of both Th1 and Th2 cytokines

Experimental autoimmune thyroiditis (EAT) can be induced by transfer of mouse thyroglobulin (MTg) and lipopolysaccharide (LPS)-immunized, MTg-activated spleen cells into syngeneic recipients. Recipients of MTg-activated T cells develop lymphocytic EAT, whereas recipients of cells activated by MTg and anti-IL-2R antibody develop a more severe and histologically distinct granulomatous form of EAT. Intravenous administration of deaggregated MTg (dMTg) 7 days before and 5 days after the first immunization of donor mice with MTg/LPS suppresses the induction of both forms of EAT. Thyroid infiltration is significantly decreased in recipients of effector cells from tolerant donors. MTg-specific T cell proliferation is partially suppressed in tolerant mice. Both IgG1 and IgG2a subclasses of anti-MTg autoantibodies are markedly inhibited in both tolerant donor mice and in recipients of tolerant spleen cells. Expression of T cell cytokine gene transcripts (IL-2, IFN gamma, IL-4, IL-10, tumor necrosis factor-alpha and transforming growth factor-beta) are all decreased in spleen cells of donor mice given dMTg. CD8+ T cells were not required for expression of tolerance since depletion of CD8+ T cells in vivo before tolerance induction or in vitro before MTg re-stimulation did not abrogate tolerance induction. Taken together, these results suggest that i.v. administration of dMTg can induce MTg-specific tolerance in both Th1- and Th2-like EAT effector cell precursors, and therefore prevent induction of adoptively transferred EAT.

T cell receptor V beta usage in murine experimental autoimmune thyroiditis

Mouse thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTg induced experimental autoimmune thyroiditis (EAT) in which the thyroid infiltrate consists primarily of mononuclear cells (MNC) (lymphocytic EAT). MTg-sensitized spleen cells cultured with MTg together with anti-IL2R antibody induce a granulomatous form of EAT in which the thyroid is infiltrated by MNC in addition to PMNs, histiocytes, and multinucleated giant cells. CD4+ T cells are the primary effector cells for both forms of EAT. The presence of specific T cell receptor (TCR) V beta families in the thyroid infiltrate was examined by flow cytometry and reverse transcription-polymerase chain reaction (RT-PCR) amplification of mRNA. At the time of maximal disease severity, cells infiltrating the thyroid expressed primarily V beta 8, V beta 4, V beta 11, and V beta 14 as determined by flow cytometry. RT-PCR confirmed these findings and also detected several additional V beta gene families, including V beta 1, V beta 2, V beta 6, V beta 13, and V beta 15; V beta 3, V beta 10, and V beta 12 were also detected in some, but not all, experiments. There were no differences in the V beta T cell repertoires in thyroids of mice with lymphocytic vs granulomatous EAT. RT-PCR analysis of intrathyroidal MNC 11 days after cell transfer showed TCR V beta mRNA transcripts to be primarily restricted to V beta 4, V beta 11, and V beta 14, whereas the predominant thyroid-infiltrating T cell 21 days after cell transfer was V beta 8+. Depletion of V beta 8+ T cells in recipient mice did not reduce EAT severity. TCR V beta usage shifted predominantly to V beta 4+, V beta 11+, or V beta 14+ T cells of both CD4+ and CD8+ T cell subsets. These results indicate that multiple V beta TCR are expressed in thyroids of mice with EAT.

The role of alpha 4 integrin and intercellular adhesion molecule-1 (ICAM-1) in murine experimental autoimmune thyroiditis

Mouse-thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTg induce a lymphocytic form of experimental autoimmune thyroiditis (EAT) whereas activation of the same cell population with MTg in the presence of anti-interleukin 2 receptor antibody (M7/20) induces a granulomatous form of EAT. The thyroid infiltrate in both lymphocytic and granulomatous EAT includes both CD4+ and CD8+ T cells and CD4+ T cells are the primary effector cells for both forms of EAT. This investigation was undertaken to begin to define the roles of alpha 4 integrin, and intercellular adhesion molecule-1 (ICAM-1) in the migration of CD4+ and CD8+ T cells to the thyroid in EAT. The studies presented here demonstrate the expression of alpha 4 integrin and ICAM-1 on CD4+ and CD8+ T cells infiltrating the thyroid and the expression of vascular cell adhesion molecule (VCAM) and ICAM-1 on thyroid cells of mice with EAT. The effects of anti-alpha 4 and anti-ICAM mAb administration on EAT severity in recipient mice was also determined. Anti-alpha 4 administration reduced or abolished lymphocyte infiltration in the thyroid resulting in reduced severity of both lymphocytic and granulomatous EAT. In contrast, anti-ICAM mAb had little effect on EAT severity. These results suggest that these two adhesion molecules exhibit differential functional roles in the modulation of EAT disease severity and that alpha 4-VCAM interactions may be of particular importance in trafficking of effector cells to the thyroid.

Suppression of murine experimental autoimmune thyroiditis by oral administration of porcine thyroglobulin

Experimental autoimmune thyroiditis (EAT) induced by the transfer of mouse thyroglobulin (MTg)-immunized spleen cells, activated in vitro with MTg, can be suppressed by oral administration of PTg to donor mice prior to immunization. Oral administration of 1 mg PTg five times over a 10-day period before immunization with MTg-LPS resulted in reduced EAT severity in recipient mice compared with recipients of cells from saline-fed immunized donors. MTg- or PTg-specific proliferative responses were not decreased in PTg-fed donors and anti-MTg antibody was not decreased in the donor mice fed 1 mg PTg. However, anti-MTg antibody production was markedly decreased in recipients of cells from PTg-fed donors compared with recipients of control cells. IgG1, IgG2A, and IgG2B anti-MTg antibody responses were all suppressed by PTg feeding suggesting that tolerance may be induced in both Th1 and Th2 cells. The more severe and histologically distinct granulomatous form of EAT was also suppressed by feeding PTg to donor mice. Studies are underway to determine the mechanism of oral tolerance in this model.

Proliferation and autoantibody production by mouse thyroglobulin (MTg)-specific B cells activated in vitro by MTg and MTg-specific T cells

Immunization of genetically susceptible strains of mice with mouse thyroglobulin (MTg) and adjuvant results in sensitization of MTg-specific CD4+ T cells that can induce experimental autoimmune thyroiditis (EAT) after in vitro activation with MTg. These MTg specific CD4+ T cells also provide help to MTg-specific B cells which produce anti-MTg autoantibodies in vivo. This study was undertaken to develop a system with which to measure MTg-specific helper function in vitro. MTg-activated T cells were shown to provide help to MTg-primed B cells in vitro as assessed by B-cell proliferation and anti-MTg autoantibody production. These responses were MTg-specific and required MTg priming of both the T- and B-cell populations. An MTg-specific CD4+ T-cell line also induced MTg-specific B-cell proliferation and was capable of inducing IgG1, IgG2a and IgG2b synthesis in MTg- primed B cells.

Requirement for B cell-derived immunoglobulin for Th activation by the type 2 antigen polyvinylpyrrolidone

Th specific for the type 2 antigen polyvinylpyrrolidone (PVP) could not be activated in vivo or in vitro in mice rendered B cell deficient by treatment from birth with anti-IgM. The requirement for B cells was apparently not due to a requirement for B cells to function as antigen presenting cells for Th activation since T cells also were not activated when anti-IgM treated mice were reconstituted with B cells prior to priming with PVP. In addition, removal of B cells from spleens of adult of adult mice had no effect on the ability of PVP to activate Th in vitro. Potential non-specific effects of chronic anti-IgM treatment on T cell function are unlikely since T cells from anti-IgM treated mice provided help to B cells for antibody responses to horse red blood cells responded normally to T cell mitogens and had a CD4:CD8 ratio like that of untreated mice; PVP primed T cells from anti-IgM treated mice also did not actively suppress the helper activity of PVP primed T cells from normal mice. In addition, PVP-specific Th were able to be activated in mice given multiple injections of anti-IgM beginning 2 weeks after birth and in mice given MOPC 104E IgM together with anti-IgM; under these conditions B cell depletion by the anti-IgM did not occur. Thus activation of PVP-specific Th requires that B cells be present during the first few weeks after birth. Experiments in which mice were given injections of normal mice Ig together with the anti-IgM indicate that the function of B cells for Th activation in this system can be replaced by B cell-derived Ig. Thus PVP-specific Th could be activated in mice treated from birth with anti-IgM plus normal Ig despite the absence of significant numbers of B cells in the spleens of these mice.

Regulation of the induction and resolution of granulomatous experimental autoimmune thyroiditis in mice by CD8+ T cells

Mouse thyroglobulin (MTg)--sensitized spleen cells activated in vitro with MTg induce experimental autoimmune thyroiditis (EAT) in which the thyroid cellular infiltrate consists primarily of mononuclear cells (lymphocytic EAT). Cells cultured with MTg plus anti-IL2R antibody induce EAT having a granulomatous histopathology. CD4+ T cells are required to induce both forms of EAT. The potential contribution of CD8+ T cells in the pathology of lymphocytic vs granulomatous EAT was addressed using anti-CD8 mAb to deplete CD8+ T cells from donor or recipient mice. Depletion of donor CD8+ T cells had little effect on EAT severity induced by cells cultured with MTg or MTg plus anti-IL2R mAb. However, recipients of CD8-depleted cells activated with MTg induced granulomatous EAT whereas cells from untreated donors activated with MTg alone induced lymphocytic EAT. Similar results were obtained when anti-CD8 mAb was added to cultures to block activation of CD8+ T cells. Injection of anti-CD8 mAb into recipient mice slightly increased the severity of EAT induced by cells cultured with MTg or MTg and anti-IL2R mAb when EAT was assessed 19-20 days after cell transfer. Cells cultured with MTg alone induced mild granulomatous EAT in most anti-CD8-treated recipients. When thyroids of mice which had granulomatous EAT on Day 19 were examined 47 or 60 days after cell transfer, the granulomatous inflammatory response in untreated recipients had almost completely resolved. In contrast, granulomatous EAT persisted and often became more severe in anti-CD8-treated recipients. Anti-CD8 treatment did not influence lymphocytic EAT assessed late after cell transfer. These results indicate that CD8+ T cells are required for the resolution of granulomatous EAT.

Differential requirement for autoantibody-producing B cells for induction of lymphocytic versus granulomatous experimental autoimmune thyroiditis

Mouse thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTG transfer experimental autoimmune thyroiditis (EAT) in which the thyroid cellular infiltrate consists primarily of mononuclear cells (lymphocytic EAT). Addition of anti-IL2R antibody to cultures with MTg leads to activation of cells that induce granulomatous EAT, accompanied by high serum anti-MTg autoantibody responses, in recipient mice. CD4+ T cells are required to induce both forms of EAT; whether B cells and/or autoantibodies produced by MTg-sensitized B cells also contribute to disease severity or the type of thyroid histopathology is unknown. In our study, B cells and autoantibody responses produced in recipient mice were reduced either by column removal of B cells from donor spleen cells or by treatment of recipient mice with anti-I-AK mAb at the time of cell transfer. These maneuvers only slightly reduced the severity of lymphocytic EAT but markedly reduced the severity and incidence of granulomatous EAT developing in recipient mice. Delaying the initiation of anti-I-AK treatment until 6 days after cell transfer was less effective in reducing anti-MTg autoantibody responses or granulomatous EAT. These studies all suggested that anti-MTg autoantibodies were required for development of granulomatous but not lymphocytic EAT. However anti-I-AK-treated recipients receiving injections of anti-MTg antibody or having serum antibody induced by prior immunization with MTg and LPS also developed less severe granulomatous EAT than controls. These results suggest that sensitized CD4+ T cells and circulating anti-MTg autoantibody are not sufficient for development of granulomatous thyroid lesions. It is possible that antibodies having a unique function or specificity are produced in mice developing granulomatous EAT or thyroid-infiltrating B cells may directly contribute to the granulomatous inflammatory response.

Differential requirement for autoantibody-producing B cells for induction of lymphocytic versus granulomatous experimental autoimmune thyroiditis

Mouse thyroglobulin (MTg)-sensitized spleen cells activated in vitro with MTG transfer experimental autoimmune thyroiditis (EAT) in which the thyroid cellular infiltrate consists primarily of mononuclear cells (lymphocytic EAT). Addition of anti-IL2R antibody to cultures with MTg leads to activation of cells that induce granulomatous EAT, accompanied by high serum anti-MTg autoantibody responses, in recipient mice. CD4+ T cells are required to induce both forms of EAT; whether B cells and/or autoantibodies produced by MTg-sensitized B cells also contribute to disease severity or the type of thyroid histopathology is unknown. In our study, B cells and autoantibody responses produced in recipient mice were reduced either by column removal of B cells from donor spleen cells or by treatment of recipient mice with anti-I-AK mAb at the time of cell transfer. These maneuvers only slightly reduced the severity of lymphocytic EAT but markedly reduced the severity and incidence of granulomatous EAT developing in recipient mice. Delaying the initiation of anti-I-AK treatment until 6 days after cell transfer was less effective in reducing anti-MTg autoantibody responses or granulomatous EAT. These studies all suggested that anti-MTg autoantibodies were required for development of granulomatous but not lymphocytic EAT. However anti-I-AK-treated recipients receiving injections of anti-MTg antibody or having serum antibody induced by prior immunization with MTg and LPS also developed less severe granulomatous EAT than controls. These results suggest that sensitized CD4+ T cells and circulating anti-MTg autoantibody are not sufficient for development of granulomatous thyroid lesions. It is possible that antibodies having a unique function or specificity are produced in mice developing granulomatous EAT or thyroid-infiltrating B cells may directly contribute to the granulomatous inflammatory response.

Intrathyroidal cell phenotype in murine lymphocytic and granulomatous experimental autoimmune thyroiditis

In-vitro mouse thyroglobulin (MTg) activated spleen cells from immunized donor mice can induce experimental autoimmune thyroiditis (EAT) after transfer to recipient mice. The intrathyroidal cellular infiltrate consists primarily of mononuclear cells (lymphocytic EAT). Cells cultured with MTg together with anti-IL2R antibody induce EAT with a granulomatous histopathology in which the thyroid infiltrate contains mononuclear cells (MNC) in addition to PMN's histiocytes, and multinucleated giant cells. Flow cytometric analysis of intrathyroidal MNC infiltrates demonstrated that both CD4+ and CD8+ T cells infiltrate the thyroid in both lymphocytic and granulomatous EAT and that CD8+ T cells outnumber CD4+ T cells. There were usually increased numbers of PMN's in the granulomatous thyroids, but low number of Ig+ and F4/80+ cells (macrophages) in the intrathyroidal infiltrate of both disease types. IL2R and Pgp-1 were expressed on both CD4+ and CD8+ intrathyroidal T cells. The majority of CD8+ cells were ICAM+, LFA-1+, and CD45RB+ whereas only a small percentage of CD4+ intrathyroidal T cells expressed these markers. There were no major differences in intrathyroidal MNC phenotype between lymphocytic and granulomatous EAT. Depletion of CD8+ T cells in recipient mice did not reduce EAT severity and resulted in an increased percentage of intrathyroidal CD4+ T cells expressing IL2R. These results suggest that CD8+ T cells are not functioning as effector cells in lymphocytic or granulomatous EAT.

Induction of granulomatous experimental autoimmune thyroiditis in mice with in vitro activated effector T cells and anti-IFN-gamma antibody

Experimental autoimmune thyroiditis (EAT) can be induced in mice after the transfer of mouse thyroglobulin (MTg)-sensitized donor spleen cells that have been activated in vitro with MTg. CD4+ T cells are required for the transfer of EAT in this model. Because CD4+ T cells produce various lymphokines, such as IFN-gamma, that may be involved in the activation or regulation of the immune response to MTg and the development of EAT, the present study was undertaken to determine whether a neutralizing mAb to IFN-gamma could modulate the induction or expression of EAT. The anti-IFN-gamma mAb XMG-1.2 had no effect on sensitization of donor cells. However, addition of XMG-1.2 mAb during in vitro activation of MTg-primed spleen cells resulted in more severe EAT in recipient mice. The thyroid lesions in recipients of cells cultured with MTg and XMG-1.2 mAb also exhibited granulomatous changes, which differed qualitatively from the predominantly lymphocytic cell infiltrates in recipients of cells cultured with MTg alone. Recipients of MTg-activated spleen cells also developed severe granulomatous EAT when they were given injections of XMG-1.2 mAb. The effects of XMG-1.2 could be neutralized by IFN-gamma. Recipients of cells cultured in the presence of XMG-1.2 mAb had augmented autoantibody responses, although there were no apparent differences in the IgG subclass distribution of the anti-MTg autoantibody responses. These studies suggest that neutralization of endogenous IFN-gamma results in increased activity of cells capable of inducing granulomatous EAT in mice.

Induction of granulomatous experimental autoimmune thyroiditis in mice with in vitro activated effector T cells and anti-IFN-gamma antibody

Experimental autoimmune thyroiditis (EAT) can be induced in mice after the transfer of mouse thyroglobulin (MTg)-sensitized donor spleen cells that have been activated in vitro with MTg. CD4+ T cells are required for the transfer of EAT in this model. Because CD4+ T cells produce various lymphokines, such as IFN-gamma, that may be involved in the activation or regulation of the immune response to MTg and the development of EAT, the present study was undertaken to determine whether a neutralizing mAb to IFN-gamma could modulate the induction or expression of EAT. The anti-IFN-gamma mAb XMG-1.2 had no effect on sensitization of donor cells. However, addition of XMG-1.2 mAb during in vitro activation of MTg-primed spleen cells resulted in more severe EAT in recipient mice. The thyroid lesions in recipients of cells cultured with MTg and XMG-1.2 mAb also exhibited granulomatous changes, which differed qualitatively from the predominantly lymphocytic cell infiltrates in recipients of cells cultured with MTg alone. Recipients of MTg-activated spleen cells also developed severe granulomatous EAT when they were given injections of XMG-1.2 mAb. The effects of XMG-1.2 could be neutralized by IFN-gamma. Recipients of cells cultured in the presence of XMG-1.2 mAb had augmented autoantibody responses, although there were no apparent differences in the IgG subclass distribution of the anti-MTg autoantibody responses. These studies suggest that neutralization of endogenous IFN-gamma results in increased activity of cells capable of inducing granulomatous EAT in mice.

Induction of severe granulomatous experimental autoimmune thyroiditis in mice by effector cells activated in the presence of anti-interleukin 2 receptor antibody

Spleen cells from CBA/J mice immunized with mouse thyroglobulin (MTg) and the adjuvant lipopolysaccharide induce experimental autoimmune thyroiditis (EAT) after transfer to recipient mice if they are first activated in vitro with MTg. EAT induced by cells cultured with MTg is generally moderate in severity and is characterized by a thyroid infiltration consisting primarily of mononuclear cells. Addition of the anti-interleukin 2 receptor (IL-2R) monoclonal antibodies (mAbs) M7/20, 3C7, or 7D4 to spleen cell cultures with MTg resulted in a cell population capable of inducing a more severe type of EAT characterized by extensive follicular destruction, granuloma formation, and the presence of multinucleated giant cells. Recipients of cells cultured with MTg and anti-IL-2R mAb also had higher anti-MTg autoantibody responses than recipients of cells cultured with MTg alone. Activation of cells capable of transferring severe granulomatous EAT and increased anti-MTg autoantibody responses required both MTg and M7/20 in culture and required addition of M7/20 within the first 8 h of the 72-h culture period. CD4+ T cells were required for the expression of both the severe granulomatous EAT lesions and the mononuclear cell infiltrates typically observed in murine EAT. The increased anti-MTg autoantibody responses in recipients of cells cultured with MTg and anti-IL-2R mAbs were not restricted to a particular immunoglobulin G (IgG) subclass and included antibody of the IgG1, IgG2A, and IgG2B subclasses. These results suggest that a subset of CD4+ T cells capable of inducing severe granulomatous EAT and increased anti-MTg autoantibody responses is preferentially activated when cells are cultured in the presence of anti-IL-2R mAb. Anti-IL-2R mAb may either prevent activation of cells that induce classical lymphocytic EAT or prevent activation of cells that normally function to downregulate EAT effector T cell activity.

Distinct populations of antigen-presenting cells are required for activation of suppressor and contrasuppressor T cells by type III pneumococcal polysaccharide

Type III pneumococcal polysaccharide (S3) coupled to spleen cells (S3-SC) has been shown to activate S3-specific Ts and Tcs in mice. Ts activation required I-J identity between carrier SC and Ts donors whereas I-A identity was required for Tcs activation. The carrier SC therefore presumably function as APC for Ts and Tcs activation by S3 since they are apparently not represented by APC present in the Ts and Tcs donors. The properties of the APC required for activation of S3-specific Ts and Tcs were determined by coupling S3 to various spleen cell subpopulations and assessing the ability of the various S3-SC populations to activate Ts and Tcs. The results indicate that Ts and Tcs are preferentially activated when S3 is presented on distinct cell types. S3-specific Ts were activated when S3 was coupled to plastic adherent cells. These cells are nonadherent to anti-Ig and nonfunctional in cyclophosphamide (Cy)-treated mice and their function is eliminated following treatment of cells with either anti-I-A or anti-I-J and C. In contrast, S3-specific Tcs were activated when S3 was coupled to anti-Ig adherent SC which bear I-A and the B cell marker J11d. These cells are functional in Cy-treated mice and their function is resistant to treatment with anti-I-J and C. Thus presentation of S3 on distinct cell types results in the preferential activation of T cells having opposing immunoregulatory function.

Requirement for B cells for activation of contrasuppressor T cells by type III pneumococcal polysaccharide

Type III pneumococcal polysaccharide (S3) is unable to activate S3-specific contrasuppressor T cells (Tcs) in mice depleted of B cells by chronic anti-IgM treatment or in immune defective xid mice that lack the B cell subset required for anti-S3 antibody responses. The inability of S3 to activate Tcs in xid mice was shown to be due to a requirement of B cells for Tcs activation rather than to an absence of Tcs in xid mice. The B cells from normal mice that are required for Tcs activation apparently function to present the S3 Ag to Tcs. S3 physically coupled to spleen cells (S3-SC) prepared from normal BCF1 SC could activate Tcs in both xid and BCF1 mice whereas S3-SC prepared from xid SC or B cell-depleted BCF1 SC could not activate Tcs in either strain. B cell APC function was abrogated by 3000 R irradiation and by treatment of the B cells with either chloroquine or paraformaldehyde. Interestingly, B cells from mice previously immunized with S3 were unable to function in Tcs activation; preimmunization of B cell donors with an irrelevant Ag or with a T-dependent form of S3 had no effect on their ability to function as APC. These latter observations are discussed in terms of the in vivo persistence of polysaccharide Ag and their ability to induce B cell tolerance under the experimental conditions used for these experiments. The results of this study provide evidence that B cells play an important and apparently obligatory role in the activation of Tcs by S3; B cells apparently function to present Ag to Tcs, resulting in the activation of this regulatory T cell subset.

Requirement for B cells for activation of contrasuppressor T cells by type III pneumococcal polysaccharide

Type III pneumococcal polysaccharide (S3) is unable to activate S3-specific contrasuppressor T cells (Tcs) in mice depleted of B cells by chronic anti-IgM treatment or in immune defective xid mice that lack the B cell subset required for anti-S3 antibody responses. The inability of S3 to activate Tcs in xid mice was shown to be due to a requirement of B cells for Tcs activation rather than to an absence of Tcs in xid mice. The B cells from normal mice that are required for Tcs activation apparently function to present the S3 Ag to Tcs. S3 physically coupled to spleen cells (S3-SC) prepared from normal BCF1 SC could activate Tcs in both xid and BCF1 mice whereas S3-SC prepared from xid SC or B cell-depleted BCF1 SC could not activate Tcs in either strain. B cell APC function was abrogated by 3000 R irradiation and by treatment of the B cells with either chloroquine or paraformaldehyde. Interestingly, B cells from mice previously immunized with S3 were unable to function in Tcs activation; preimmunization of B cell donors with an irrelevant Ag or with a T-dependent form of S3 had no effect on their ability to function as APC. These latter observations are discussed in terms of the in vivo persistence of polysaccharide Ag and their ability to induce B cell tolerance under the experimental conditions used for these experiments. The results of this study provide evidence that B cells play an important and apparently obligatory role in the activation of Tcs by S3; B cells apparently function to present Ag to Tcs, resulting in the activation of this regulatory T cell subset.

Type 6 and 19 pneumococcal polysaccharides coupled to erythrocytes elicit pneumococcal cell wall-specific primary IgM responses and capsular polysaccharide-specific secondary IgG responses

Previous results have shown that the primary murine antibody responses to vaccine preparations of type 6 (S6; Danish type 6A) or type 19 (S19; Danish type 19F) pneumococcal capsular polysaccharides consist entirely of IgM antipneumococcal cell wall carbohydrate (PnC)-specific antibodies. No capsular polysaccharide-specific IgM antibodies were detectable by plaque-forming cell or enzyme-linked immunosorbent assay techniques. In this report, antibodies specific for S6 and S19 capsular polysaccharides were induced in secondary responses to chicken erythrocyte (CRBC) conjugates of S6 and S19. Essentially all detectable IgG produced in the secondary response was capsular polysaccharide specific and included all subclasses of IgG. In contrast, all detectable IgM produced in the primary response to S6-CRBC and S19-CRBC, and the IgM produced in the secondary response to S6-CRBC was not capsular polysaccharide specific since it reacted with PnC. Thus, there is a major change in the specificity of the primary IgM response compared to the secondary IgG response of mice immunized with S6-CRBC or S19-CRBC. Injection of PnC or any PnC-containing polysaccharide prior to immunization with S6-CRBC or S19-CRBC resulted in suppression of the primary IgM response. In contrast, only the capsular polysaccharide used in the immunizing polysaccharide-erythrocyte conjugate suppressed induction of the capsular polysaccharide-specific secondary IgG response. These results suggest that S6 and S19 capsular polysaccharide-specific IgG-producing memory B cells derive from capsular polysaccharide-specific precursors which do not produce detectable antibody after primary immunization.

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)

Production and characterization of monoclonal antibodies specific for types 6 and 19 pneumococcal capsular polysaccharides

The primary IgM and the secondary IgG antibody responses to pneumococcal capsular polysaccharides type 19 (S19) and type 6 (S6) coupled to sheep erythrocytes (S19-SRBC or S6-SRBC) differ in specificity. Although the primary IgM response appears to be totally specific for the pneumococcal cell wall carbohydrate (PnC) which is present in these polysaccharide preparations, the secondary IgG response appears to be completely specific for the immunizing capsular polysaccharide. A library of B cell hybridomas from fusions of splenocytes undergoing a primary response to an S19 preparation consisted entirely of PnC-specific hybrids. Thus, no evidence was obtained for the presence of capsular polysaccharide-specific IgM secreting B cells. IgM and IgG antibody secreting hybridomas were obtained, from fusions of splenocytes undergoing secondary S6- or S19-SRBC responses, to examine the antigen specificity of secondary antibody response of B cells at the clonal level. Many of the secondary IgM hybridomas secreted PnC-specific antibody; however, several S6-specific IgM secreting hybrids were also obtained, demonstrating a previously undetected population of B cells. All IgG secreting hybridomas obtained from S19- or S6-SRBC secondary response fusions secreted capsular polysaccharide-specific antibody, thus confirming the apparent absence of PnC-specific IgG secreting B cells in these responses. This method of immunization and challenge of mice with capsular polysaccharide coupled to erythrocytes, which results in the production of capsular polysaccharide-specific IgG responses, offers a relatively straightforward means to generate monoclonal antibodies specific for pneumococcal capsular polysaccharides.

Regulation of IgG responses by helper and suppressor T cells activated by pneumococcal capsular polysaccharides

Type 2 antigens are usually unable to prime the helper T cells (TH) required for secondary IgG antibody responses. However, previous results from this laboratory indicated that low doses of the type 2 antigen polyvinylpyrrolidone (PVP) could activate T cells which provided help to PVP-primed B cells for the production of PVP-specific IgG antibody. Therefore, it was of interest to determine if other type 2 antigens may also be able to activate TH. Low doses of S19 or S3 (subimmunogenic for a primary IgM response) activated TH capable of providing help to S19- or S3-CRBC-primed B cells for a secondary IgG response. Higher doses of these antigens (optimally immunogenic for a primary IgM response) activated suppressor T cells (TS). Removal of these TS prior to transfer of T cells to recipient mice resulted in expression of TH function. Therefore, the preferential activation of TH versus TS was dependent on the dose of antigen used for priming. TH activated by low doses of S19 expressed Thy 1 and L3T4 and were antigen specific. In contrast to the ability of low doses of PVP to prime B cells for secondary IgG responses, low doses of S3 and S19 did not prime capsular polysaccharide-specific IgG memory B cells. High doses of S3 were able to prime B cells if TS precursors were first removed by treatment of mice with cyclophosphamide (Cy), whereas high doses of S19 did not prime B cells for secondary IgG responses in either Cy-treated or control mice. These results are discussed in relation to the general observations that type 2 antigens may not activate antigen-specific TH.

Prevention and reversal of experimental autoimmune thyroiditis (EAT) in mice by administration of anti-L3T4 monoclonal antibody at different stages of disease development

Experimental autoimmune thyroiditis (EAT) can be induced in CBA/J mice following the transfer of spleen cells from mouse thyroglobulin (MTg)-sensitized donors that have been activated in vitro with MTg. Since L3T4+ T cells are required to transfer EAT in this model, the present study was undertaken to assess the effectiveness of the anti-L3T4 monoclonal antibody (mAb) GK1.5 in preventing or arresting the development of EAT. Spleen cells from mice given mAb GK1.5 prior to sensitization with MTg and adjuvant could not transfer EAT to normal recipients and cells from these mice did not proliferate in vitro to MTg. Donor mice given GK1.5 before immunization did not develop anti-MTg autoantibody and recipients of cells from such mice also produced little anti-MTg. GK1.5 could also prevent the proliferation and activation of sensitized effector cell precursors when added to in vitro cultures. When a single injection of mAb GK1.5 was given to recipients of in vitro-activated spleen cells, EAT was reduced whether the mAb was given prior to cell transfer or as late as 19 days after cell transfer. Whereas the incidence and severity of EAT was consistently reduced by injecting recipient mice with GK1.5, the same mice generally had no reduction in anti-MTg autoantibody. Since EAT is consistently induced in control recipients by 14-19 days after cell transfer, the ability of mAb GK1.5 to inhibit EAT when injected 14 or 19 days after cell transfer indicates that a single injection of the mAb GK1.5 can cause reversal of the histopathologic lesions of EAT in mice. These studies further establish the important role of L3T4+ T cells in the pathogenesis of EAT in mice and also suggest that therapy with an appropriate mAb may be an effective treatment for certain autoimmune diseases even when the therapy is initiated late in the course of the disease.

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.

Augmentation of transfer of experimental autoimmune thyroiditis (EAT) in mice by irradiation of recipients

Experimental autoimmune thyroiditis (EAT) can be adoptively transferred to normal syngeneic recipients using spleen cells from susceptible strains of mice primed in vivo with mouse thyroglobulin (MTg) and lipopolysaccharide (LPS) following in vitro activation of spleen cells by culture with MTg. Irradiation of recipient animals markedly augments the severity of thyroiditis induced in this system. Irradiation of recipients does not alter the time course of the development of thyroiditis, nor does it alter the requirement for both in vivo priming and in vitro activation of spleen cells for the development of EAT. Spleen cells from EAT-resistant strains of mice (e.g., Balb/c) do not induce EAT in irradiated recipients. Irradiated recipients develop significant levels of anti-MTg antibodies while unirradiated recipients have little detectable antibody response. The augmenting effect of irradiation can be substantially reversed by transferring naive spleen cells to recipients prior to the transfer of MTg/LPS-primed in vitro-activated spleen cells. In addition athymic CBA/Tufts nude mice develop more severe EAT than CBA/Tufts nude/+ littermates following transfer of activated CBA/J spleen cells. These data suggest that natural suppressor cells may regulate the development of EAT at the effector cell level.

In vitro activation of specific helper and suppressor T cells by the type 2 antigen polyvinylpyrrolidone (PVP)

Although type 2 antigens, such as PVP, generally do not activate specific TH, previous studies have established that low doses of PVP (0.0025 microgram) can activate TH in vivo which provide help in primed B cells for PVP-specific IgG responses. Doses of PVP that are optimally immunogenic for IgM antibody production (0.25 to 25 micrograms) preferentially activate PVP-specific TS, which suppress IgG antibody production. In the studies reported here, TH and TS that regulate PVP-specific IgG antibody responses were activated in vitro by culturing normal spleen cells for 4 days with PVP. Induction of the TH and TS is dependent upon the amount of PVP in culture: 10(-4) micrograms PVP activates TH, whereas 10(-2) micrograms PVP preferentially activates TS. TH induced in vitro express Thy-1, L3T4, and I-A determinants and help provided by these TH is similar in magnitude to that provided by TH from mice primed with 0.0025 microgram PVP in vivo. TH can also be activated in vitro if donor mice are treated with Cy before culture of their spleen cells with 10(-2) micrograms PVP. Cy pretreatment prevents TS activation, and TH are then induced in these cultures. The presence of TS does not prevent activation of TH by 10(-2) micrograms PVP, because removal of TS by treatment of T cells with anti-Lyt-2 + complement at the end of culture uncovers TH activity. This TH activity is comparable with that of TH obtained after culture with 10(-4) micrograms PVP. The ability to activate PVP-specific TH and TS in vitro should allow determination of the mechanisms involved in activation of T cells by type 2 antigens and the mechanisms by which TS and TH interact with one another.

In vitro activation of specific helper and suppressor T cells by the type 2 antigen polyvinylpyrrolidone (PVP)

Although type 2 antigens, such as PVP, generally do not activate specific TH, previous studies have established that low doses of PVP (0.0025 microgram) can activate TH in vivo which provide help in primed B cells for PVP-specific IgG responses. Doses of PVP that are optimally immunogenic for IgM antibody production (0.25 to 25 micrograms) preferentially activate PVP-specific TS, which suppress IgG antibody production. In the studies reported here, TH and TS that regulate PVP-specific IgG antibody responses were activated in vitro by culturing normal spleen cells for 4 days with PVP. Induction of the TH and TS is dependent upon the amount of PVP in culture: 10(-4) micrograms PVP activates TH, whereas 10(-2) micrograms PVP preferentially activates TS. TH induced in vitro express Thy-1, L3T4, and I-A determinants and help provided by these TH is similar in magnitude to that provided by TH from mice primed with 0.0025 microgram PVP in vivo. TH can also be activated in vitro if donor mice are treated with Cy before culture of their spleen cells with 10(-2) micrograms PVP. Cy pretreatment prevents TS activation, and TH are then induced in these cultures. The presence of TS does not prevent activation of TH by 10(-2) micrograms PVP, because removal of TS by treatment of T cells with anti-Lyt-2 + complement at the end of culture uncovers TH activity. This TH activity is comparable with that of TH obtained after culture with 10(-4) micrograms PVP. The ability to activate PVP-specific TH and TS in vitro should allow determination of the mechanisms involved in activation of T cells by type 2 antigens and the mechanisms by which TS and TH interact with one another.

Suppression of IgG memory responses by T cells activated with the type 2 antigen polyvinylpyrrolidone (PVP)

Although type 2 antigens, such as polyvinylpyrrolidone (PVP), generally do not prime for IgG memory responses or activate specific helper T cells (TH), previous studies have established that low doses of PVP (0.0025 microgram) can prime for IgG memory and induce TH in vivo. Doses of PVP that are optimally immunogenic for IgM antibody production (0.25-25 micrograms) do not prime for IgG memory responses and preferentially activate PVP-specific suppressor T cells (TS) which suppress IgG antibody production. The studies reported here further characterize PVP-specific TS and begin to investigate the mode of action of these TS. TS induced with high doses of PVP have a typical suppressor cell surface phenotype in that they are Lyt 2+, I-J+, L3T4-, I-A- T cells. PVP-specific TS are inducible in mice expressing the X-linked immune defect and are Igh restricted in their actions. These TS suppress PVP-specific IgG responses of PVP-HRBC (horse red blood cells)-primed B cells when the TH population is from low-dose PVP-primed mice but not when the TH population is from PVP-HRBC-primed mice. Thus the TS do not apparently directly suppress the B-cell responses but act indirectly to suppress IgG responses by preventing the expression of PVP-specific TH function. The TS induced by 0.25 microgram PVP also prevent the generation of PVP-specific memory B cells apparently by preventing the expression of functional TH which are required for induction of memory B cells. Elimination of TS activation by pretreatment of mice with cyclophosphamide at the time of priming with 0.25 microgram PVP results in the expression of TH function and priming of memory B cells.

Characterization of helper T cells induced by the type 2 antigen polyvinylpyrrolidone

Type 2 antigens are usually unable to prime for IgG memory responses or to activate helper T cells (TH) necessary for memory B cell generation. Previous studies from this laboratory have established that low doses (0.0025 microgram) of polyvinylpyrrolidone (PVP) or a T-dependent form of PVP, PVP-coupled horse red blood cells (PVP-HRBC) can activate PVP-specific TH. The present study was undertaken in order to determine some of the characteristics of the TH activated by PVP and to compare their properties with those of classical TH1 and of TH2 cells described in many T-dependent systems. TH activated with either 0.0025 microgram of PVP or PVP-HRBC were characterized with respect to cell surface antigens, Igh restriction and generation in mice expressing an X-linked immune defect (xid mice). PVP-specific TH are similar to TH1 cells in that they are required for the production of IgG subclasses absent in primary responses and have the Lyt-1+, L3T4+, I-J-surface phenotype. These TH may not be identical with TH1 cells, however, since they are I-A+ and Igh restricted. PVP-specific TH can be generated in xid mice which do not produce antibody in a primary anti-PVP response and do not develop a memory response to PVP, regardless of whether it is presented as a type 2 or T-dependent antigen.

Characterization of helper T cells induced by the type 2 antigen polyvinylpyrrolidone

Type 2 antigens are usually unable to prime for IgG memory responses or to activate helper T cells (TH) necessary for memory B cell generation. Previous studies from this laboratory have established that low doses (0.0025 microgram) of polyvinylpyrrolidone (PVP) or a T-dependent form of PVP, PVP-coupled horse red blood cells (PVP-HRBC) can activate PVP-specific TH. The present study was undertaken in order to determine some of the characteristics of the TH activated by PVP and to compare their properties with those of classical TH1 and of TH2 cells described in many T-dependent systems. TH activated with either 0.0025 microgram of PVP or PVP-HRBC were characterized with respect to cell surface antigens, Igh restriction and generation in mice expressing an X-linked immune defect (xid mice). PVP-specific TH are similar to TH1 cells in that they are required for the production of IgG subclasses absent in primary responses and have the Lyt-1+, L3T4+, I-J-surface phenotype. These TH may not be identical with TH1 cells, however, since they are I-A+ and Igh restricted. PVP-specific TH can be generated in xid mice which do not produce antibody in a primary anti-PVP response and do not develop a memory response to PVP, regardless of whether it is presented as a type 2 or T-dependent antigen.

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.

Characterization and activity of contrasuppressor T cells induced by type III pneumococcal polysaccharide

Optimally immunogenic amounts of type III pneumococcal polysaccharide (S3) activate a population of contrasuppressor T cells (Tcs), which have been shown to play an important role in the induction of anti-S3 antibody responses. These Tcs belong to a unique T cell subset that has the surface phenotype Lyt 1+2- L3T4- I-J+ I-A+. These Tcs are also cyclophosphamide (Cy)-sensitive and sensitive to antilymphocyte serum (ALS) and mitomycin C. Tcs have antigen-binding receptors, indicating that any interactions of Tcs with B cells or T suppressor cells (Ts) (both of which also have antigen-binding receptors) must be via an antigen bridge rather than an idiotype-anti-idiotype interaction. Tcs are also Igh restricted in their action. Contrasuppression is manifest only when the Tcs are Igh compatible with both the Ts and the responding B cells. Tcs apparently mediate their effects by releasing a soluble factor, since a soluble factor extracted from Tcs is able to abrogate the effects of S3-specific Ts.