The obese strain (OS) of chickens with spontaneous autoimmune thyroiditis: review of recent data

Infectobesity: Obesity of Infectious Origin

The rapid increase in obesity and the associated health care costs have prompted a search for better approaches for its prevention and management. Such efforts may be facilitated by better understanding the etiology of obesity. Of the several etiological factors, infection, an unusual causative factor, has recently started receiving greater attention. In the last two decades, 10 adipogenic pathogens were reported, including human and nonhuman viruses, scrapie agents, bacteria, and gut microflora. Some of these pathogens are associated with human obesity, but their causative role in human obesity has not been established. This chapter presents information about the natural hosts, signs and symptoms, and pathogenesis of the adipogenic microorganisms. If relevant to humans, "Infectobesity" would be a relatively novel, yet extremely significant concept. A new perspective about the infectious etiology of obesity may stimulate additional research to assess the contribution of hitherto unknown pathogens to human obesity and possibly to prevent or treat obesity of infectious origins.

Avian models with spontaneous autoimmune diseases

Autoimmune diseases in human patients only become clinically manifest when the disease process has developed to a stage where functional compensation by the afflicted organ or system is not possible anymore. In order to understand the initial etiologic and pathogenic events that are generally not yet accessible in humans, appropriate animal models are required. In this respect, spontaneously developing models--albeit rare--reflect the situation in humans much more closely than experimentally induced models, including knockout and transgenic mice. The present chapter describes three spontaneous chicken models for human autoimmune diseases, the Obese strain (OS) with a Hashimoto-like autoimmune thyroiditis, the University of California at Davis lines 200 and 206 (UCD-200 and -206) with a scleroderma-like disease, and the amelanotic Smyth line with a vitiligo-like syndrome (SLV). Special emphasis is given to the new opportunities to unravel the genetic basis of these diseases in view of the recently completed sequencing of the chicken genome.

Immunogenetic analysis of spontaneous autoimmune thyroiditis of obese strain chickens

A variety of immunological, endocrinological, and virological abnormalities have been implicated in the etiopathogenesis of spontaneous autoimmune thyroiditis (SAT) of Obese strain (OS) chickens, e.g., a general T cell hyperreactivity, an increased uptake of iodine into the thyroid gland, a diminution of the glucocorticoid tonus, and an OS-specific endogenous virus. In crosses of the close-bred OS B15/B15 subline with the inbred normal CB B12/B12 strain we have studied the mode of inheritance of these aberrations and their putative association with SAT. The results indicate that none of these OS-specific characteristics alone is an absolute prerequisite for the development of thyroid infiltration, which appears to be governed by one autosomal recessive gene.

Hypothesis: immunogenetic analysis of spontaneous autoimmune thyroiditis in obese strain (OS) chickens: a two-gene family model

Analysis of the number of genes involved in the regulation of the expression of SAT in OS, by means of crosses with the unrelated inbred CB line, gave the following results: 1) The production of Tg-AAb is regulated by one or two genes; 2) the sensitivity of the thyroid to autoimmune attack is under the control of about 3 genes; 3) the expression of SAT, as measured by mononuclear cell infiltration of the thyroid gland, is thus encoded by at least 4-5 genes (approximately 2 of which regulate the immune system hyperreactivity against antigens of the thyroid, and 3 of which regulate the sensitivity of the target organ to an attack by the immune system. It should, however, not be forgotten that this calculation, which results in 5 genes as being crucial for the development of SAT, is only valid for the combination of the OS and the CB inbred line. A different number might have arisen with the use of a different inbred line for crossing experiments. 4) The genes involved in the genetic control of SAT can be divided into two categories, major and minor genes. One family of major genes regulates the hyperreactivity of the immune system and perhaps its specificity for thyroid antigens. A second family of major genes encodes the target organ susceptibility to the attack of the immune system. The minor genes modulate the expression of the major genes and are especially important in animals with an incomplete set of major genes. The influence of sex hormones and the MHC are examples of such genes. MHC genes play an important role in outbred populations, but they are not a prerequisite for the development of the disease. Fully developed, early onset SAT is only seen in an animal where all major genes are present. The existence of two-gene families, each composed of relatively few genes, might guarantee to a species that SAT will not be too frequent in outbred populations.

The role of genetically-determined primary alterations of the target organ in the development of spontaneous autoimmune thyroiditis in obese strain (OS) chickens

Immunologists working in the field of autoimmunity tend to concentrate all their efforts on the elucidation of possible malfunctions of the immune system, particularly pathologic changes of immune regulation. Also in the OS model various groups of investigators emphasized this approach, although it was already clear early in the history of this model that SAT has a multigenic background. The fact that this disease cannot be transferred into normal, histocompatible animals without an appropriate non-MHC linked genetic background was a strong indication that detailed studies of thyroid-associated factors may be warranted for the elucidation of the pathogenesis of this disease and perhaps also its human counterpart, Hashimoto thyroiditis. Since several reviews on the immunologic aspects in the OS model have been published in recent years we have in this communication attempted to discuss the - mostly still rudimentary - findings concerning the target organ itself, including morphological changes before the beginning of infiltration, the analysis of Tg, the altered thyroid function before onset of SAT, the results of cross-breeding studies of OS and inbred normal chickens in respect to the susceptibility of the offspring for the transfer of SAT, the possible role of a virus infection and the aberrant expression of MHC class II antigens on TEC. Cross-breeding studies revealed that most probably a single gene is responsible for the primary altered thyroid function and at least 3 genes code for the susceptibility of the OS thyroid gland to the autoimmune attack. It is not yet clear for which of the above-mentioned observations each of these genes is responsible and what is/are the initial triggering mechanism(s). Ongoing studies in our laboratory concentrate on this question, specifically the potential role of endogenous viruses in this process.

Effect of testosterone treatments for varying periods on autoimmune development and on specific infiltrating leukocyte populations in the thyroid gland of obese strain chickens

Spontaneous autoimmune thyroiditis (SAT) is detectable by 2 weeks of age in the obese (OS) strain of chicken, and by 6 weeks virtually all of these animals have severe lymphoid infiltration of the thyroid. During the interval from hatching to 6 weeks of age, testosterone implants were administered for varying periods. All treatment groups were terminated at 6 weeks. Testosterone administered shortly after hatching increased thymus weight, depressed bursa weight, and reduced the severity of SAT, as measured by lymphoid infiltration of the thyroid and circulating thyroglobulin autoantibody concentrations. Birds supplemented with testosterone at later intervals exhibited depressed bursa and thymus weight; however, the severity of SAT was not affected. In a second experiment, the treated group was administered testosterone for the first 2 weeks after hatching. Thyroids were histologically examined at 2 and 6 weeks using a panel of five monoclonal antibodies (anti-Ia, anti-IgM, anti-IgG, anti-T cell, and antithymocyte). Compared with untreated controls, testosterone treatment reduced the frequency of Ia+ cells, T cells, and IgG+ cells in the thyroid. This treatment did not affect the frequency of IgM+ cells, and perhaps slightly increased the frequency of thymocytes. These results suggest that testosterone's suppressive effects are associated with changes in thymic development and effector T-cell and regulator T-cell activity.

Spontaneous autoimmune thyroiditis in obese strain chickens: a genetic analysis of target organ abnormalities

In this study we investigated the genetic background of primary abnormalities found in the thyroid gland of Obese strain (OS) chickens with spontaneous autoimmune thyroiditis (SAT), i.e., susceptibility to passively transferred antibodies to thyroglobulin (TgAb) and incomplete suppression of iodine uptake by thyroxine (T4). Several crosses between the B15/B15 subline of OS chickens and the inbred CB line (B12/B12) were done and the progeny was analyzed for thyroiditis after injection of OS serum containing high titers of TgAb. It was found that passive transfer of TgAb increased the lymphoid infiltration in the thyroids of OS chickens, but had no effect on CB birds. A genetic analysis of backcrosses revealed that this trait is, in the case of simple Mendelian inheritance, encoded by at least three recessive genes. The thyroidal 131I uptake of these crosses under T4 was also determined and we found that this trait is most probably encoded by only one recessive gene.

Effects of testosterone on the development of autoimmune thyroiditis in two strains of chicken

The effect of testosterone on organ-specific spontaneous autoimmune thyroiditis (SAT) was examined in two strains of chicken: the Obese (OS) strain, which develops SAT at several weeks of age and the control Special C (Sp. C) strain. Both were originally selected from the C strain and are homozygous for the B13 major histocompatibility haplotype. Testes development and testosterone levels in the OS strain were considerably less than those found in comparably aged birds of the Sp. C strain. Testosterone supplementation of the OS strain significantly decreased thyroid infiltration by lymphocytes while castration of the Sp. C strain significantly enhanced infiltration. These results suggest that testosterone reduces SAT and that the hormonal constitution in both strains of chicken affect the frequency of occurrence and severity of this disorder.

MHC- and non-MHC-encoded surface antigens of chicken lymphoid cells and erythrocytes recognized by polyclonal xeno-, allo- and monoclonal antibodies

Surface antigens on chicken thymus and bursa cells were analyzed by immunoprecipitation using polyclonal and monoclonal antisera raised against (and specific for) thymus (ATS) or bursa (ABS) cells, respectively. The antigens identified were compared with those governed by the B-F, B-L and B-G regions of the chicken major histocompatibility complex (B complex). Four proteins were precipitated from thymus cells by 2 polyclonal ATS: both antisera recognized molecules of apparent molecular mass of 172-182, 132-135, 75-76 kDa, and one antiserum in addition recognized a protein of 102 kDa. The 172-182 and 102-kDa peaks were still demonstrable under reducing conditions indicating that they are composed of a single polypeptide chain, the other 2 were lost under reducing conditions, therefore, must be composed of smaller subunits. Of the 2 monoclonal ATS tested, one identified a single protein of 186 kDa and the other a 135-kDa protein (in addition to 2 smaller molecules); whether these are the same as those precipitated by the polyclonal antisera remains to be determined as they behaved differently under reducing conditions. Proteins of 162 and 78-84 kDa were revealed by 2 polyclonal ABS under nonreducing conditions but the former may in one case be a polymer (it disappeared under reducing conditions) and in the other a single molecule. In addition molecules of 182 kDa were identified by one antiserum and of 84 and 60 kDa by the other under nonreducing conditions. Of the 4 monoclonal ABS only one identified a 200-kDa protein: molecules of 115-125, 90-100, 48-52 and 40-43 kDa were also precipitated, all of which were reduced to smaller molecules. With 2 specific anti-B-F alloantisera we were able to precipitate the "conventional" B-F antigen from red blood cell lysates of CB-strain chickens resolving into a 40-kDa peak and a light chain of about 12 kDa corresponding to beta 2 microglobulin. Precipitates from peripheral blood lymphocytes, bursa and thymus cells revealed an additional protein of 22 kDa. With 2 specific B-L alloantisera two peaks of 33 kDa and 31 kDa were obtained from peripheral blood lymphocytes. Using anti-B-G alloantisera a double band corresponding to 47 and 42 kDa was seen under reducing conditions. There is no evidence from these data to indicate that the polyclonal and monoclonal antibodies are directed towards major histocompatibility complex antigens.

Nonthyroid autoantibodies in obese strain (OS) chickens

Organ-specific autoantibodies (AAb) to thyroid and non-thyroid antigens of various endocrine and exocrine glands (glandular stomach, pancreas, adrenal, parathyroid, and striated muscle) were determined by different serological procedures in sera from Obese strain (OS), Cornell C strain (CS), normal inbred strains (CC and CB), and outbred normal White Leghorn (NWL) chickens. Thyroglobulin autoantibodies (Tg-AAbs), evaluated by immunodiffusion, passive hemagglutination, enzyme-linked immunosorbent assay, and indirect immunofluorescence, as well as other organ-specific AAbs determined by indirect immunofluorescence, predominated in OS chickens. Tg-AAbs were found in the highest frequency, thyroid microsomal AAbs in intermediate frequency, and the other organ-specific AAbs in low frequency in OS chickens. Thyroid and non-thyroid organ-specific AAbs were found only occasionally in control chickens and then only in low titers. Thus, spontaneous autoimmune thyroiditis of OS chickens correlates closely with human Hashimoto thyroiditis not only in respect to AAbs to thyroid antigens but also to nonthyroid organ-specific antigens. Non-organ-specific AAbs, such as antinuclear antibodies, antibodies to chicken red blood cell nuclei, mitochondrial AAbs, smooth muscle antibodies, and reticulin AAbs occur in high frequency in all strains of chickens tested. Even a slight prevalence in NWL chickens was seen, indicating that the abnormal immune response in OS chickens is restricted to organ-specific antigens of the thyroid gland and in some cases also to other exocrine or endocrine glands.

"Natural" chicken antibodies to red blood cells are mainly directed against the B-G antigen, and their occurrence is independent of spontaneous autoimmune thyroiditis

Using an indirect hemagglutination assay we tested sera from 94 healthy normal White Leghorn (NWL) and 117 Obese strain (OS) chickens with spontaneous autoimmune thyroiditis for the presence of "natural" antibodies against major histocompatibility complex (MHC) antigens expressed on red blood cells (RBC). In both groups older animals had a significantly increased frequency of such antibodies, but the titer was age-independent. OS chickens showed almost the same frequency of natural antibodies as NWL, and a comparison between OS birds with high antithyroglobulin autoantibody (TgAAb) titers and those with low titers also did not reveal a significant difference. We conclude that the occurrence of natural antibodies has no relation to TgAAb. The specificity of natural antibodies for MHC-encoded antigens was investigated in indirect immunofluorescence tests including absorption experiments with RBC and white blood cells (WBC). This analysis revealed that of 14 MHC-specific sera 13 were reacting with the B-G antigen, which is present on RBC only. One serum reacted with the B-F antigen, expressed on all somatic cells, i.e., both on RBC and WBC.

Immunofluorescence studies on the codistribution immune deposits and complement in the thyroid glands of Obese strain (OS) chickens

This study demonstrates immune complexes in thyroid glands of Obese strain (OS) chickens, that consist of thyroglobulin (Tg) and antibodies to Tg. In IIF tests it was shown that these complexes fix complement with an age-dependent increase from 12% in 19-day-old embryos up to 100% in 6-week-old animals. This finding and the observation that the deposition of complement-binding immune complexes precede cellular infiltration of the thyroid gland and correlate with the serum titer of Tg-Ab (as one parameter of the disease) points towards a role as one initial effector mechanism for the development of spontaneous autoimmune thyroiditis (SAT).

Effect of cyclosporin A on spontaneous autoimmune thyroiditis of Obese strain (OS) chickens

The spontaneous autoimmune thyroiditis (SAT) which develops in the Obese strain (OS) of chickens depends on an intact B-dependent portion of immune system. T helper cells have been shown to be required for the production of thyroglobulin autoantibodies (Tg-AAb), but a possible contribution of cytotoxic T cells in the initial phases of SAT still remains to be elucidated. Cyclosporin A (CsA), an immunosuppressive drug with selective activity on T blast formation was used as a probe to clarify this issue: (a) the immunosuppressive potential of CsA was first verified for an avian species by demonstrating prolongation of skin allograft survival; (b) posthatching treatment of OS chickens with CsA until they were killed at 3 weeks of age did not alter the frequency and severity of SAT and the incidence and titer of Tg-AAb; (c) treatment of OS embryos on days 15, 17 and 19 of incubation entailed the development of significantly more severe disease and higher titers of Tg-AAb as compared to controls. A possible effect of CsA on precursors of suppressor T cells in the chicken is postulated. Cytotoxic T cells seem to play a minor role in the beginning of thyroid infiltration. It is concluded that CsA may not be the drug of choice for treatment of at least some autoimmune diseases.

The role of self-antigen in the development of autoimmunity in Obese strain chickens with spontaneous autoallergic thyroiditis

Neonatal thyroidectomy of Obese strain (OS) chickens showed that the spontaneous development of thyroid autoimmunity in these animals was fully dependent upon the presence of autoantigen, and could not be ascribed essentially to antigen-independent mechanisms such as polyclonal lymphocyte activation or innate distortions within the idiotype network. Similarly, removal of the gland in animals with established thyroiditis demonstrated the need for antigen to maintain the autoimmune response. Thyroglobulin from normal chickens induced autoantibodies in neonatally thyroidectomized OS birds, suggesting that an abnormality in the structure of this protein is not a prerequisite for the development of autoimmunity. This contention is supported by the finding that OS and normal thyroglobulin were immunochemically indistinguishable, whether compared using OS autoantibodies or rabbit anti-chicken thyroglobulin sera.

Chicken major histocompatibility complex and disease

The chicken MHC (B complex) initially described by Briles as controlling blood antigens, is now known to be composed of at least three regions, L, F and G. Two of these, F and G, were described on the basis of recombinants found in a study of over 10,000 chickens. On the basis of biochemical, tissue distribution and functional analyses, F corresponds to the murine H-2 K/D regions. The G region is unique to the chicken since the antigenic product is expressed only on erythrocytes and their progenitors. L was identified by serological studies and corresponds to the H-2 I region; the L antigen is expressed predominantly on B lymphocytes, monocytes and 10% of T lymphocytes, and differences in the L region result in variations in immune responsiveness. A number of functional similarities exist between the chicken MHC and that of other species such as regulation of graft rejection, graft-versus-host reaction (GVHR) and mixed lymphocyte reactions (MLR), mitogenic and immune responsiveness and resistance to RNA and DNA virus infection. The chicken MHC also controls the severity of autoimmune disease, as exemplified by the spontaneous thyroiditis of Obese strain (OS) chickens. It differs from mammalian MHC's by having of lower crossing-over frequency and no apparent gene duplication.