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

Obesity is associated with subclinical hypothyroidism in the presence of thyroid autoantibodies: a cross-sectional study

BACKGROUND

Both obesity and subclinical hypothyroidism (SCH) have adverse effects on human body, but the relationship between these two conditions remains inconsistent. The presence of thyroid autoantibodies influences thyroid hormone levels, and may further mediate the interaction between obesity and SCH. This study aimed to explore the association among obesity, SCH and thyroid autoantibodies.

METHODS

This study was a cross-sectional survey of 2505 subjects. Obesity was defined as a body mass index ≥28 kg/m². Serum concentrations of thyroid hormones, thyroid peroxidase antibody (TPO-Ab) and thyroglobulin antibody (Tg-Ab) were examined. Logistic analysis was used to explore the relation among obesity, SCH and thyroid autoantibodies.

RESULTS

A proportion of 11.54% (289/2505) subjects were obese, and 165 subjects had SCH. The positive rates of thyroid autoantibodies, TPO-Ab and Tg-Ab were 17.64% (442/2505), 11.02% (276/2505) and 14.13% (354/2505), respectively. The proportion of SCH was significantly higher in obese than nonobese subjects among those with positive thyroid autoantibodies [22.41% (13/58) vs. 11.72% (45/384), p = 0.025, χ2 test]. Moreover, obesity was significantly associated with SCH in the presence of thyroid autoantibodies after adjusting for confounding factors (OR 2.212, 95% CI 1.103 to 4.433, p = 0.025). A higher proportion of subjects with obesity had Tg-Ab positivity [17.99% (52/289) vs. 13.63% (302/2216), p = 0.045, χ2 test], and obesity remained significantly associated with Tg-Ab positivity by multiple logistic analysis (OR 1.504, 95% CI 1.077 to 2.101, p = 0.017).

CONCLUSIONS

Obesity was associated with SCH in the presence of thyroid autoantibodies. Examination of SCH is recommended in obese subjects with thyroid autoantibody positivity.

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.

The effect of soluble complement receptor 1 (sCR1) and human thyroid antibodies on the course of experimental autoimmune thyroiditis in rats

Experimental autoimmune thyroiditis (EAT), induced by immunisation of rats with thyroid extract and complete Freund's adjuvant, has been used as a model to study the effects of complement inhibition mediated by soluble complement receptor 1 (sCR1) administration during the initial phase of the disease. There was no effect of sCR1 on the severity of thyroiditis at day 28 after immunisation or on the levels of thyroid antibodies, whether sCR1 was given during the first or second week after immunisation. Human IgG containing high levels of thyroid peroxidase antibodies given to rats at the time of immunisation caused significant worsening of thyroiditis severity (P < 0.01 compared to animals receiving normal IgG) but sCR1 again had no effect in this variant of the EAT model. The results indicate that complement does not play a major role in the initial phase of tissue injury in EAT and complement inhibition does not impair the generation of an autoimmune response against the thyroid, although it remains possible that complement activation is important during the chronic phase of disease maintenance in human autoimmune thyroid disease.

Preferential TCR V beta 1 gene usage by autoreactive T cells in spontaneous autoimmune thyroiditis of the obese strain of chickens

We studied T cell receptor variable beta (TCR V beta) gene usage by autoreactive T cells in spontaneous autoimmune thyroiditis (SAT) of obese strain (OS) chickens. Chicken alpha beta T cells may express either V beta 1 or V beta 2 genes, the products of which can be recognized by TCR2 and TCR3 monoclonal antibodies, respectively. Selective depletion of V beta 1+ or V beta 2+ T cells in OS chickens was accomplished by repeated injections of TCR2 or TCR3 antibodies into embryonic and 1-3-week-old chickens. The birds were killed at 20 days of age and their spleens and thyroid glands evaluated by immunohistochemistry. We found that V beta 1+ T cells preferentially infiltrated OS chicken thyroid glands. Antibody treatments resulted in a 41% reduction in frequency of V beta 1+, and a 87% reduction of the frequency of V beta 2+ cells in the circulation, and in a profound decrease of the respective T cells in spleens and thyroid glands. Selective suppression of V beta 1+ T cells partially inhibited SAT development in that thyroid-infiltrating cells and destruction of thyroid follicles were reduced by more than 50%. Thyroglobulin autoantibody serum levels were also reduced in V beta 1+ T cell-depleted OS chickens, whereas selective depletion of V beta 2+ T cells did not inhibit SAT development. These findings indicate preferential TCR V beta 1 gene usage by autoreactive T cells in SAT of OS chickens.

Target organ susceptibility and autoantibody production in an animal model of spontaneous autoimmune thyroiditis

F1-hybrids of Obese strain (OS) chickens, afflicted with spontaneous autoimmune thyroiditis (SAT), and normal, inbred CB chickens, do not develop severe thyroiditis. About 50% of these crosses show circulating autoantibodies to thyroglobulin (TgAAb), but the thyroid glands are only slightly infiltrated, suggesting that the target organ is not susceptible to autoimmune attack. In the present study we show that despite this mild infiltration TgAAb are only synthesized by lymphoid cells within the thyroid gland. Furthermore, we demonstrate that immunization with chicken thyroglobulin (Tg) in complete Freund's adjuvant causes severe experimental autoimmune thyroiditis (EAT) in F1(OSxCB) hybrids.

Experimentally-induced autoimmune myocarditis: production of heart myosin-specific autoantibodies within the inflammatory infiltrate

Immunization with cardiac myosin in complete Freund's adjuvant (CFA) induces severe autoimmune myocarditis in A H-2 congenic mouse strains. The disease shares a variety of characteristics with Coxsackie-virus B3 (CB3)-induced myocarditis and is strongly associated with high-titered autoantibodies to cardiac myosin. Using the spot ELISA-technique, we demonstrate here that in cardiac myosin-immunized mice myosin autoantibodies were not only produced within the spleen, but also at the site of the autoimmune attack, i.e., within the inflammatory heart infiltrate. At the level of single plasma cells we further showed that a substantial part of the myosin autoantibodies was specific for the cardiac myosin isoform, thereby supporting previous serologic data. The finding that cells of the inflammatory heart infiltrate significantly contribute to autoantibody production might explain why the occurrence of high-titered myosin autoantibodies is restricted to mice which develop the disease.

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.

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.