Clin. exp. Immunol. (1990) 80, 1-3
EDITORIAL REVIEW
Thyroid peroxidase as an antigen in autoimmune thyroiditis A. P. WEETMAN Department ofMedicine, University of Cambridge Clinical School, Addenbrooke's Hospital, Cambridge, England
(Acceptedfor publication 8 February 1990)
Shortly after the seminal discovery of antibodies to thyroglobulin in Hashimoto's thyroiditis, a second group of antibodies against the thyroid was identified in these patients; unlike those against thyroglobulin, the new autoantibodies were capable of complement fixation (Trotter, Belyavin & Wadhams, 1957). Binding characteristics in cell fractionation experiments led to these being termed thyroid microsomal antibodies, but although intracytoplasmic staining of thyroid cells was found with Hashimoto's thyroiditis sera in immunofluorescence studies, there was also strong binding of the autoantibodies along the apical, microvillar border (Roitt et al., 1964). These features suggested that the autoantibodies binding to the cell surface could have pathogenic significance in mediating tissue injury, as the result of complement attack and antibody-dependent cell
sequent studies have verified that TPO accounts for virtually all of the antigenic determinants recognized by microsomal antibodies in autoimmune thyroiditis (Kotani et al., 1986; Mariotti et al.,
1987).
TPO is a haem-containing enzyme that catalyses both the iodination of tyrosine and the coupling of these iodinated tyrosines to form thyroid hormones (Taurog, 1986). As such it is central to thyroid function, and congenital absence of the enzyme results in profound thyroid failure which leads to a rare type of goitrous cretinism. The primary structures of human and porcine TPO have been deduced from cDNA clones (Kimura et al., 1987; Libert et al., 1987; Seto et al., 1987) and these show considerable homology. The human TPO gene maps to the short arm of chromosome 2 and contains both nuclear and mitochondrial gene modules. It may give rise to two proteins, differing by 6 2 kb, through alternate splicing of the gene. The two proteins appear to co-exist, giving rise to a doublet of 100107 kD on SDS-PAGE. Comparison of cDNA sequences from TPO clones and microsomal antigen clones provided conclusive proof that these were identical. There was also found to be 42% primary structural homology with the neutrophil enzyme, myeloperoxidase. TPO gene transcription and translation are both under the positive control of thyroid-stimulating hormone (TSH) (Magnusson & Rapoport, 1985; Chazenbalk, Magnusson & Rapoport, 1987). Enhanced expression of TPO by cultured thyroid cells has also been reported with a combination of lectin plus interferon-gamma (Iwatani et al., 1987); this could involve the stimulation of contaminating mononuclear cells, present in such cultures, which release other cytokines rather than a direct effect. A new generation of studies on the thyroid microsomal antigen has been initiated by these observations, giving rise to unexpected questions. It has become clear that microsomal antibodies are heterogenous. The antibodies against native TPO correspond to those detected by the standard microsomal haemagglutination test used in clinical diagnosis, but other antibodies from a proportion of patients with thyroiditis react to denatured or reduced TPO (Hamada et al., 1987). It is not known whether these define particular patient subsets. At least six B cell epitopes have been identified, including one or both of the catalytic sites involved in peroxidation (Kohno et al., 1986; Doble et al., 1988), but it is unclear whether antibodies against these sites contribute to hypothyroidism by blocking hormone synthesis in vivo. TPO autoantibodies from most patients with thyroiditis cross-react with myeloperoxidase in reduced or denatured form (Banga et al., 1989); it remains to be established
cytotoxicity. The antigenic identity of the intracellular microsomes and the thyroid cell surface antigen was suggested by the close correlation of microsomal antibody activity determined by haemagglutination and the presence of surface-reactive antibodies detected by indirect immunofluorescence using cultured thyroid cells (Khoury et al., 1981). This was confirmed with monoclonal antibodies to the human microsomal antigen which had similar binding and cytotoxic properties in primary thyroid cell cultures (Weetman et al., 1985). Moreover, these antibodies bound in a species-specific fashion to the cytoplasmic and microvillar antigen on human thyroid cells with exactly the same localization, by double-immunofluorescence, as human autoantibodies (Banga et al., 1986). Despite the expression of this antigen only on the apical cell surface (which lies within the thyroid follicle), immunoglobulin deposited in vivo was localized at this site in the glands of patients with Graves' disease and Hashimoto's thyroiditis, indicating that the microsomal antigen seemed surprisingly accessible to autoantibodies (Khoury, Bottazzo & Roitt, 1984). Immunprecipitation and immunoblotting studies revealed that the thyroid microsomal antigen was a poorly glycosylated protein of 105-107 kD, which lost at least one epitope for autoantibody binding when in the reduced state (Banga et al., 1985; Hamada et al., 1985). It was then found that this protein was in fact thyroid peroxidase (TPO); the binding to thyroid cell membranes of a monoclonal antibody raised against TPO was strongly inhibited by microsomal antibodies from patients with autoimmune thyroid disease (Czarnocka et al., 1985). SubCorrespondence: A. P. Weetman, Department of Medicine, University of Cambridge Clinical School, Addenbrooke's Hospital, Level 5, Cambridge CB2 2QQ, UK.
1
2
A. P. Weetman
whether this has any relevance in viho, although neutropenia and anti-neutrophil antibodies (of undetermined fine specificity) have been described in Graves' disease (Weitzman et al., 1985). There is also a shared epitope between TPO and thyroglobulin which might explain the frequent (but not inevitable) concurrence of these two autoantibodies (Kohno et al., 1988). The report by Naito et al. (1990) in this issue has extended this by demonstrating very frequent cross-reactivity between TPO and thyroglobulin antibodies from patients with autoimmune thyroiditis but not with antibodies from ostensibly healthy subjects. This again suggests the presence of autoantigenic epitopes which are pathogenic and which delineate particular subsets of patients. The immune response to the thyroid microsomal antigen is now also being addressed in experimental autoimmune thyroiditis. Early attempts, using immunization with crude microsomal preparations, showed that thyroiditis could indeed by induced in rabbits and monkeys (Kite, Argue & Rose, 1966; Mangkornkanok, Marcowitz & Battifora, 1972), but with the identification of TPO as the antigen which can be obtained with reasonable purity, there has been renewed interest in such animal models. Two recent studies have been published in this journal. In the first, in the February issue, by McLachlan et al. (1990), two strains of mice were immunized with porcine TPO. TPO antibodies (against the porcine but not murine antigen) were produced by CBA/J mice (strain H-2k, also known to be high responders to thyroglobulin), but there was a disappointing absence of thyroiditis; BALB/c mice (strain H-2d) developed neither antibodies nor thyroiditis. The second study is in this issue (Kotani et al., 1990), in which only C57BL/6 and C57BL/ 10 mice (both H-2b) were found to develop severe thyroiditis following porcine TPO immunization, explaining the failure of the preceding study to detect such lesions. Thus experimental thyroiditis induced by thyroglobulin shows very different genetic restriction to that produced by TPO. Another feature of this paper is that the thyroid damage did not correlate with antibody production against porcine TPO, or the rare appearance of antibodies against murine TPO. Similar observations have been made in murine thyroiditis induced by thyroglobulin immunization (Kong, 1986), but then thyroglobulin antibodies are known not to fix complement (probably due to the autoantigenic epitope distribution on the thyroglobulin molecule). The independence of thyroid infiltration and TPO antibodies is underscored by the transfer of disease with a TPOspecific T cell line; as in thyroglobulin-induced experimental thyroiditis, vaccination with T cells attenuated by irradiation conferred protection against the transfer of subsequent disease, presumably through the generation of anti-idiotypic suppressor cells (Cohen, 1989). These results emphasize the potential for TPO-specific, T cell-dependent mechanisms in the pathogenesis of thyroiditis; however, it should be noted that the lesions in these immunized mice were insufficient to alter circulating hormone levels (although thyroidal radioiodine uptake was impaired). Thus a role for tissue damage by complement-fixing microsomal antibodies in autoimmune hypothyroidism remains likely. In Graves' disease, concurrent stimulation by TSH receptor antibodies presumably outweighs the destructive effects of the immune response against TPO; late in disease, hypothyroidism often supervenes. The induction of experimental thyroiditis by homologous rather than heterologous TPO may provide a
better model and result in TPO antibody production so that the B cell contribution to disease can be studied in detail, but sufficient material will be difficult to obtain except by recombinant DNA technology. The murine studies also point to involvement of at least two genes in the control of the thyroiditis induced by TPO, one of which is non-H-2 linked. There are preliminary reports of a TPO gene polymorphism associated with Graves' disease (Mangklabruks et al., 1988), raising the possibility of antigenic variability contributing to the autoimmune response. Identification of T and B cell autoantigenic epitopes should soon clarify this and also result in further dissection of the autoimmune response to the thyroid in mouse and man, particularly regarding the effector mechanisms which employ TPO to mediate thyroid damage. REFERENCES BANGA, J.P., MIRAKIAN, R., HAMMOND, L., PRYCE, G., BIDEY, S., BOTTAZZO, F., WEETMAN, A.P., MCGREGOR, A.M. & RoITT, I.M. (1986) Characterization of monoclonal antibodies directed towards the microsomal/microvillar thyroid autoantigen recognized by Hashimoto autoantibodies. Clin. exp. Immunol. 64, 544. BANGA, J.P., PRYCE, G., HAMMOND, L. & ROITT, I.M. (1985) Structural features of the autoantigens involved in thyroid autoimmune disease: the thyroid microsomal/microvillar antigen. Mol. Immunol. 22, 629. BANGA, J.P., TOMLINSON, R.W.S., DOBLE, N., ODELL, E. & MCGREGOR, A.M. (1989) Thyroid microsomal/thyroid peroxidase autoantibodies show discrete patterns of cross-reactivity to myeloperoxidase, lactoperoxidase and horseradish peroxidase. Immunology, 67, 197. CHAZENBALK, G., MAGNUSSON, R.P. & RAPOPORT, B. (1987) Thyrotropin stimulation of cultured thyroid cells increases steady state levels of the messenger ribonucleic acid for thyroid peroxidase. Mol. Endocrinol. 1, 913. COHEN I.R. (1989) T cell vaccination and suppression of autoimmune disease. In Progress in Immunology vol. VII (ed. by F. Melchers) p. 867. Springer-Verlag, Berlin. CZARNOCKA, B., RUF, J., FERRAND, M., CARAYON, P. & LISSITZY, S. (1985) Purification of the human thyroid peroxidase and its identification as the microsomal antigen involved in autoimmune thyroid diseases. FEBS Lett. 190, 147. DOBLE, N.D., BANGA, J.P., POPE, R., LALOR, E., KILDUFF, P. & McGREGOR, A.M. (1988) Autoantibodies to the thyroid microsomal/ thyroid peroxidase antigen are polyclonal and directed to several distinct antigenic sites. Immunology, 64, 23. HAMADA, N., GRIMM, C., MORI, H. & DEGROOT, L.J. (1985) Identification of a thyroid microsomal antigen by western blot and immunoprecipitation. J. clin. Endocrinol. Metab. 61, 120. HAMADA, N., JAEDUCK, N., PORTMANN, L., ITO, K. & DEGROOT, L.J. (1987) Antibodies against denatured and reduced thyroid microsomal antigen in autoimmune thyroid disease. J. clin. Endocrinol. Metab. 64, 230. IWATANI, Y., IITAKA, M., GERSTEIN, H.C., Row, V.V. & VOLPtE, R. (1987) Separate induction of MHC and thyroid microsomal antigen (Mc Ag) expression on thyroid cell monolayers: enhancement of lectin-induced Mc Ag expression by interferon-gamma. J. clin. Endocriniol. Metab. 64, 1302. KHOURY, E.L., BOTTAZZO, G.F. & RoITT, I.M. (1984) The thyroid 'microsomal' antigen revisited. Its paradoxical binding in vivo to the apical surface of the follicular epithelium. J. erp. Med. 159, 577. KHOURY, E.L., HAMMOND, L., BOTTAZZO, G.F. & DONIACH, D. (1981) Presence of the organspecific 'microsomal' autoantigen on the surface of human thyroid cells in culture: its involvement with the complement-mediated cytotoxicity. Clin exp. Immunol. 45, 316. KIMURA, S., KOTANI, T., MCBRIDE, O.M., UNICKI, K., HIRAI, K.,
TPO in autoimmune thyroiditis NAKEYAMA, T. & OHTAKI, S. (1987) Human thyroid peroxidase: complete cDNA and protein sequence, chromosome mapping and identification of two alternately spliced mRNAs. Proc. natl Acad. Sci. USA, 84, 5555. KITE, J.H., ARGUE, H. & ROSE, N.R. (1966) Experimental thyroiditis in the rhesus monkey. I. Cytotoxic, mixed-agglutinating and complement-fixing antibodies. Clin. exp. Immunol. 1, 139. KOHNO, Y., HIYAMA, Y., SHIMOJO, N., NAKAJIMA, H. & Hosoyo, T. (1986) Autoantibodies to thyroid peroxidase in patients with chronic thyroiditis: effect of antibody binding on enzyme activities. Clin. exp. Immunol. 65, 534. KOHNO, Y., NAITO, N., HIYAMA, Y., SHIMOJO, N., SUZUKI, N., TARUTANI, O., NiiMi, H., NAKAJIMA, H. & HOSOYA, T. (1988) Thyroglobulin and thyroid peroxidase share common epitopes recognized by autoantibodies from patients with chronic autoimmune thyroiditis. J. clin. Endocriniol. Metab. 67, 899. KONG, A.M. (1986) The mouse model of autoimmune thyroid disease. In Immunology of Endocrine Diseases (ed. by A. M. McGregor) p. 1. MTP Press, Lancaster. KOTANI, T., UMEKI, K., HIRAI, K. & OHTAKI, S. (1990) Experimental murine thyroiditis induced by porcine thyroid peroxidase and its transfer by the antigen-specific T cell line. Clin. exp. Immunol. 80, 11. KOTANI, T., UMEKI, K., MATSUNAGA, S., KATO, E. & OHTAKI, S. (1986) Detection of autoantibodies to thyroid peroxidase in autoimmune thyroid diseases by micro-ELISA and immunoblotting. J. clin. Endocrinol. Metab. 62, 928. LIBERT, F., RUEL, J., LUDGATE, M., SWILLENS, S., ALEXANDER, N., VASSART, G. & DINSART, C. (1987) Thyroperoxidase, an auto-antigen with a mosaic structure made of nuclear and mitochondrial gene modules. EMBO J. 6, 4193. MAGNUSSON, R.P. & RAPOPORT, B. (1985) Modulation of differentiated function in cultured thyroid cells: thyrotropin control of thyroid peroxidase activity. Endocriniology, 116, 1493. MANGKLABRUKS, A., RAPOPORT, B., MAGNUSSON, R. & DEGROOT, L.J. (1988) Thyroid peroxidase (TPO) gene polymorphism in autoimmune thyroid diseases (AITD). In 70th Annual Meeting of The Endocrine Society, New Orleans. Abstract 1034.
3
MANGKORNKANOK, M., MARCOWITZ, A.S. & BATTIFORA, H.A. (1972) Chronic thyroiditis in the rabbit induced with homologous thyroid microsomes. Science, 178, 316. MARIOTTI, S., ANELLI, S., RUF, J., BECHI, R., CZARNOCKA, B., LOMBARDI, A., CARAYON, P. & PINCCHERA, A. (1987) Comparison of serum thyroid microsomal and thyroid peroxidase autoantibodies in thyroid diseases. J. clin. Endocrinol. Metab. 65, 987. McLACHLAN, S.M., ATHERTON, M.C., NAKAJIMA, Y., NAPIER, J., JORDAN, R.K., CLARK, F. & REES SMITH, B. (1990) Thyroid peroxidase and the induction of autoimmune thyroid disease. Clin. exp. Immunol. 79, 182. NAITO, N., SAITO, K., HOSOYA, T., TARUTANI, O., SAKATA, S., NISHIKAWA, T., NiiMI, H., HAKAJIMA, H. & KoHNo, Y. (1990) Antithyroglobulin autoantibodies in sera from patients with chronic thyroiditis and from healthy subjects: differences in cross-reactivity with thyroid peroxidase. Clin. exp. Immunol. 80, 4. Roirr, I., LING, N.R., DONIACH, D. & COUCHMAN, K.G. (1964) The cytoplasmic autoantigen of the human thyroid. I. Immunological and biochemical characteristics Immunology, 7, 375. SETO, P., HIRAYU, H., MAGNUSSON, R.P., GESTAUTAS, J., PORTMANN, L., DEGROOT, L.J. & RAPOPORT, B. (1987) Isolation of a complementary DNA clone for thyroid microsomal antigen. Homology with the gene for thyroid peroxidase. J. clin. Invest. 80, 1205. TAUROG, A. (1986) Hormone synthesis: thyroid iodine metabolism. In The Thyroid, 5th edn (ed. by S. H. Ingbar & L. E. Bravermar) p. 53, J. B. Lippincott, Philadelphia. TROTTER, W.R., BELYAVIN, G. & WADHAMS, A. (1957) Precipitating and complement-fixing antibodies in Hashimoto's disease. Proc. R. Soc.
Med. 50, 961. WEETMAN, A.P., GUNN, C.A., RENNIE, D.P., HALL, R. & MCGREGOR, A.M. (1985) The production and characterization of monoclonal antibodies to the human thyroid microsome. J. Endocrinol. 105, 47. WEITZMAN, S.A., STOSSEL, T.A., HARMON, D.C., DANIELS, G., MALOOF, F. & RIDGEWAY, E.C. (1985) Antineutrophil autoantibodies in Graves' disease. Implications of thyrotropin binding to neutrophils. J. clin. Invest. 75, 119.
EDITORIAL REVIEW
Thyroid peroxidase as an antigen in autoimmune thyroiditis A. P. WEETMAN Department ofMedicine, University of Cambridge Clinical School, Addenbrooke's Hospital, Cambridge, England
(Acceptedfor publication 8 February 1990)
Shortly after the seminal discovery of antibodies to thyroglobulin in Hashimoto's thyroiditis, a second group of antibodies against the thyroid was identified in these patients; unlike those against thyroglobulin, the new autoantibodies were capable of complement fixation (Trotter, Belyavin & Wadhams, 1957). Binding characteristics in cell fractionation experiments led to these being termed thyroid microsomal antibodies, but although intracytoplasmic staining of thyroid cells was found with Hashimoto's thyroiditis sera in immunofluorescence studies, there was also strong binding of the autoantibodies along the apical, microvillar border (Roitt et al., 1964). These features suggested that the autoantibodies binding to the cell surface could have pathogenic significance in mediating tissue injury, as the result of complement attack and antibody-dependent cell
sequent studies have verified that TPO accounts for virtually all of the antigenic determinants recognized by microsomal antibodies in autoimmune thyroiditis (Kotani et al., 1986; Mariotti et al.,
1987).
TPO is a haem-containing enzyme that catalyses both the iodination of tyrosine and the coupling of these iodinated tyrosines to form thyroid hormones (Taurog, 1986). As such it is central to thyroid function, and congenital absence of the enzyme results in profound thyroid failure which leads to a rare type of goitrous cretinism. The primary structures of human and porcine TPO have been deduced from cDNA clones (Kimura et al., 1987; Libert et al., 1987; Seto et al., 1987) and these show considerable homology. The human TPO gene maps to the short arm of chromosome 2 and contains both nuclear and mitochondrial gene modules. It may give rise to two proteins, differing by 6 2 kb, through alternate splicing of the gene. The two proteins appear to co-exist, giving rise to a doublet of 100107 kD on SDS-PAGE. Comparison of cDNA sequences from TPO clones and microsomal antigen clones provided conclusive proof that these were identical. There was also found to be 42% primary structural homology with the neutrophil enzyme, myeloperoxidase. TPO gene transcription and translation are both under the positive control of thyroid-stimulating hormone (TSH) (Magnusson & Rapoport, 1985; Chazenbalk, Magnusson & Rapoport, 1987). Enhanced expression of TPO by cultured thyroid cells has also been reported with a combination of lectin plus interferon-gamma (Iwatani et al., 1987); this could involve the stimulation of contaminating mononuclear cells, present in such cultures, which release other cytokines rather than a direct effect. A new generation of studies on the thyroid microsomal antigen has been initiated by these observations, giving rise to unexpected questions. It has become clear that microsomal antibodies are heterogenous. The antibodies against native TPO correspond to those detected by the standard microsomal haemagglutination test used in clinical diagnosis, but other antibodies from a proportion of patients with thyroiditis react to denatured or reduced TPO (Hamada et al., 1987). It is not known whether these define particular patient subsets. At least six B cell epitopes have been identified, including one or both of the catalytic sites involved in peroxidation (Kohno et al., 1986; Doble et al., 1988), but it is unclear whether antibodies against these sites contribute to hypothyroidism by blocking hormone synthesis in vivo. TPO autoantibodies from most patients with thyroiditis cross-react with myeloperoxidase in reduced or denatured form (Banga et al., 1989); it remains to be established
cytotoxicity. The antigenic identity of the intracellular microsomes and the thyroid cell surface antigen was suggested by the close correlation of microsomal antibody activity determined by haemagglutination and the presence of surface-reactive antibodies detected by indirect immunofluorescence using cultured thyroid cells (Khoury et al., 1981). This was confirmed with monoclonal antibodies to the human microsomal antigen which had similar binding and cytotoxic properties in primary thyroid cell cultures (Weetman et al., 1985). Moreover, these antibodies bound in a species-specific fashion to the cytoplasmic and microvillar antigen on human thyroid cells with exactly the same localization, by double-immunofluorescence, as human autoantibodies (Banga et al., 1986). Despite the expression of this antigen only on the apical cell surface (which lies within the thyroid follicle), immunoglobulin deposited in vivo was localized at this site in the glands of patients with Graves' disease and Hashimoto's thyroiditis, indicating that the microsomal antigen seemed surprisingly accessible to autoantibodies (Khoury, Bottazzo & Roitt, 1984). Immunprecipitation and immunoblotting studies revealed that the thyroid microsomal antigen was a poorly glycosylated protein of 105-107 kD, which lost at least one epitope for autoantibody binding when in the reduced state (Banga et al., 1985; Hamada et al., 1985). It was then found that this protein was in fact thyroid peroxidase (TPO); the binding to thyroid cell membranes of a monoclonal antibody raised against TPO was strongly inhibited by microsomal antibodies from patients with autoimmune thyroid disease (Czarnocka et al., 1985). SubCorrespondence: A. P. Weetman, Department of Medicine, University of Cambridge Clinical School, Addenbrooke's Hospital, Level 5, Cambridge CB2 2QQ, UK.
1
2
A. P. Weetman
whether this has any relevance in viho, although neutropenia and anti-neutrophil antibodies (of undetermined fine specificity) have been described in Graves' disease (Weitzman et al., 1985). There is also a shared epitope between TPO and thyroglobulin which might explain the frequent (but not inevitable) concurrence of these two autoantibodies (Kohno et al., 1988). The report by Naito et al. (1990) in this issue has extended this by demonstrating very frequent cross-reactivity between TPO and thyroglobulin antibodies from patients with autoimmune thyroiditis but not with antibodies from ostensibly healthy subjects. This again suggests the presence of autoantigenic epitopes which are pathogenic and which delineate particular subsets of patients. The immune response to the thyroid microsomal antigen is now also being addressed in experimental autoimmune thyroiditis. Early attempts, using immunization with crude microsomal preparations, showed that thyroiditis could indeed by induced in rabbits and monkeys (Kite, Argue & Rose, 1966; Mangkornkanok, Marcowitz & Battifora, 1972), but with the identification of TPO as the antigen which can be obtained with reasonable purity, there has been renewed interest in such animal models. Two recent studies have been published in this journal. In the first, in the February issue, by McLachlan et al. (1990), two strains of mice were immunized with porcine TPO. TPO antibodies (against the porcine but not murine antigen) were produced by CBA/J mice (strain H-2k, also known to be high responders to thyroglobulin), but there was a disappointing absence of thyroiditis; BALB/c mice (strain H-2d) developed neither antibodies nor thyroiditis. The second study is in this issue (Kotani et al., 1990), in which only C57BL/6 and C57BL/ 10 mice (both H-2b) were found to develop severe thyroiditis following porcine TPO immunization, explaining the failure of the preceding study to detect such lesions. Thus experimental thyroiditis induced by thyroglobulin shows very different genetic restriction to that produced by TPO. Another feature of this paper is that the thyroid damage did not correlate with antibody production against porcine TPO, or the rare appearance of antibodies against murine TPO. Similar observations have been made in murine thyroiditis induced by thyroglobulin immunization (Kong, 1986), but then thyroglobulin antibodies are known not to fix complement (probably due to the autoantigenic epitope distribution on the thyroglobulin molecule). The independence of thyroid infiltration and TPO antibodies is underscored by the transfer of disease with a TPOspecific T cell line; as in thyroglobulin-induced experimental thyroiditis, vaccination with T cells attenuated by irradiation conferred protection against the transfer of subsequent disease, presumably through the generation of anti-idiotypic suppressor cells (Cohen, 1989). These results emphasize the potential for TPO-specific, T cell-dependent mechanisms in the pathogenesis of thyroiditis; however, it should be noted that the lesions in these immunized mice were insufficient to alter circulating hormone levels (although thyroidal radioiodine uptake was impaired). Thus a role for tissue damage by complement-fixing microsomal antibodies in autoimmune hypothyroidism remains likely. In Graves' disease, concurrent stimulation by TSH receptor antibodies presumably outweighs the destructive effects of the immune response against TPO; late in disease, hypothyroidism often supervenes. The induction of experimental thyroiditis by homologous rather than heterologous TPO may provide a
better model and result in TPO antibody production so that the B cell contribution to disease can be studied in detail, but sufficient material will be difficult to obtain except by recombinant DNA technology. The murine studies also point to involvement of at least two genes in the control of the thyroiditis induced by TPO, one of which is non-H-2 linked. There are preliminary reports of a TPO gene polymorphism associated with Graves' disease (Mangklabruks et al., 1988), raising the possibility of antigenic variability contributing to the autoimmune response. Identification of T and B cell autoantigenic epitopes should soon clarify this and also result in further dissection of the autoimmune response to the thyroid in mouse and man, particularly regarding the effector mechanisms which employ TPO to mediate thyroid damage. REFERENCES BANGA, J.P., MIRAKIAN, R., HAMMOND, L., PRYCE, G., BIDEY, S., BOTTAZZO, F., WEETMAN, A.P., MCGREGOR, A.M. & RoITT, I.M. (1986) Characterization of monoclonal antibodies directed towards the microsomal/microvillar thyroid autoantigen recognized by Hashimoto autoantibodies. Clin. exp. Immunol. 64, 544. BANGA, J.P., PRYCE, G., HAMMOND, L. & ROITT, I.M. (1985) Structural features of the autoantigens involved in thyroid autoimmune disease: the thyroid microsomal/microvillar antigen. Mol. Immunol. 22, 629. BANGA, J.P., TOMLINSON, R.W.S., DOBLE, N., ODELL, E. & MCGREGOR, A.M. (1989) Thyroid microsomal/thyroid peroxidase autoantibodies show discrete patterns of cross-reactivity to myeloperoxidase, lactoperoxidase and horseradish peroxidase. Immunology, 67, 197. CHAZENBALK, G., MAGNUSSON, R.P. & RAPOPORT, B. (1987) Thyrotropin stimulation of cultured thyroid cells increases steady state levels of the messenger ribonucleic acid for thyroid peroxidase. Mol. Endocrinol. 1, 913. COHEN I.R. (1989) T cell vaccination and suppression of autoimmune disease. In Progress in Immunology vol. VII (ed. by F. Melchers) p. 867. Springer-Verlag, Berlin. CZARNOCKA, B., RUF, J., FERRAND, M., CARAYON, P. & LISSITZY, S. (1985) Purification of the human thyroid peroxidase and its identification as the microsomal antigen involved in autoimmune thyroid diseases. FEBS Lett. 190, 147. DOBLE, N.D., BANGA, J.P., POPE, R., LALOR, E., KILDUFF, P. & McGREGOR, A.M. (1988) Autoantibodies to the thyroid microsomal/ thyroid peroxidase antigen are polyclonal and directed to several distinct antigenic sites. Immunology, 64, 23. HAMADA, N., GRIMM, C., MORI, H. & DEGROOT, L.J. (1985) Identification of a thyroid microsomal antigen by western blot and immunoprecipitation. J. clin. Endocrinol. Metab. 61, 120. HAMADA, N., JAEDUCK, N., PORTMANN, L., ITO, K. & DEGROOT, L.J. (1987) Antibodies against denatured and reduced thyroid microsomal antigen in autoimmune thyroid disease. J. clin. Endocrinol. Metab. 64, 230. IWATANI, Y., IITAKA, M., GERSTEIN, H.C., Row, V.V. & VOLPtE, R. (1987) Separate induction of MHC and thyroid microsomal antigen (Mc Ag) expression on thyroid cell monolayers: enhancement of lectin-induced Mc Ag expression by interferon-gamma. J. clin. Endocriniol. Metab. 64, 1302. KHOURY, E.L., BOTTAZZO, G.F. & RoITT, I.M. (1984) The thyroid 'microsomal' antigen revisited. Its paradoxical binding in vivo to the apical surface of the follicular epithelium. J. erp. Med. 159, 577. KHOURY, E.L., HAMMOND, L., BOTTAZZO, G.F. & DONIACH, D. (1981) Presence of the organspecific 'microsomal' autoantigen on the surface of human thyroid cells in culture: its involvement with the complement-mediated cytotoxicity. Clin exp. Immunol. 45, 316. KIMURA, S., KOTANI, T., MCBRIDE, O.M., UNICKI, K., HIRAI, K.,
TPO in autoimmune thyroiditis NAKEYAMA, T. & OHTAKI, S. (1987) Human thyroid peroxidase: complete cDNA and protein sequence, chromosome mapping and identification of two alternately spliced mRNAs. Proc. natl Acad. Sci. USA, 84, 5555. KITE, J.H., ARGUE, H. & ROSE, N.R. (1966) Experimental thyroiditis in the rhesus monkey. I. Cytotoxic, mixed-agglutinating and complement-fixing antibodies. Clin. exp. Immunol. 1, 139. KOHNO, Y., HIYAMA, Y., SHIMOJO, N., NAKAJIMA, H. & Hosoyo, T. (1986) Autoantibodies to thyroid peroxidase in patients with chronic thyroiditis: effect of antibody binding on enzyme activities. Clin. exp. Immunol. 65, 534. KOHNO, Y., NAITO, N., HIYAMA, Y., SHIMOJO, N., SUZUKI, N., TARUTANI, O., NiiMi, H., NAKAJIMA, H. & HOSOYA, T. (1988) Thyroglobulin and thyroid peroxidase share common epitopes recognized by autoantibodies from patients with chronic autoimmune thyroiditis. J. clin. Endocriniol. Metab. 67, 899. KONG, A.M. (1986) The mouse model of autoimmune thyroid disease. In Immunology of Endocrine Diseases (ed. by A. M. McGregor) p. 1. MTP Press, Lancaster. KOTANI, T., UMEKI, K., HIRAI, K. & OHTAKI, S. (1990) Experimental murine thyroiditis induced by porcine thyroid peroxidase and its transfer by the antigen-specific T cell line. Clin. exp. Immunol. 80, 11. KOTANI, T., UMEKI, K., MATSUNAGA, S., KATO, E. & OHTAKI, S. (1986) Detection of autoantibodies to thyroid peroxidase in autoimmune thyroid diseases by micro-ELISA and immunoblotting. J. clin. Endocrinol. Metab. 62, 928. LIBERT, F., RUEL, J., LUDGATE, M., SWILLENS, S., ALEXANDER, N., VASSART, G. & DINSART, C. (1987) Thyroperoxidase, an auto-antigen with a mosaic structure made of nuclear and mitochondrial gene modules. EMBO J. 6, 4193. MAGNUSSON, R.P. & RAPOPORT, B. (1985) Modulation of differentiated function in cultured thyroid cells: thyrotropin control of thyroid peroxidase activity. Endocriniology, 116, 1493. MANGKLABRUKS, A., RAPOPORT, B., MAGNUSSON, R. & DEGROOT, L.J. (1988) Thyroid peroxidase (TPO) gene polymorphism in autoimmune thyroid diseases (AITD). In 70th Annual Meeting of The Endocrine Society, New Orleans. Abstract 1034.
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