Thyroid follicular cell function after non-lethal complement membrane attack

Diversity of complement activation in different thyroid diseases

OBJECTIVE

To investigate complement components expression in both thyroid tissues and serum from patients with Hashimoto's thyroiditis (HT), Graves' disease (GD), and papillary thyroid cancer (PTC).

METHODS

C1q, mannose binding lectin (MBL), Bb, C4d, C3d and membrane attack complex (MAC) (C5b-9) deposition and complement regulate proteins (CD46, CD55 and CD59) expression in thyroid tissues from HT, GD, PTC, and control groups were examined by IHC. C1q, MBL, Bb, C4d, C3a, and soluble C5b-9 (sC5b-9) serum levels in the HT, GD, PTC, and healthy donor (HD) groups were measured by ELISAs.

RESULTS

MAC deposition was detected in thyroid tissues in the HT, GD and PTC groups, but not the control group. MBL, Bb, C4d, C3d and MAC staining intensities in thyroid tissues were significantly higher in the HT and PTC groups than in the control group (all P < 0.05). The C1q level was higher in HT tissues than in control tissues (both P < 0.05). No complement component had a significant difference in staining intensities between the GD and control groups. CD55 and CD59 expression levels in thyroid tissues were higher in the PTC group than in the HT, GD and control groups (all P < 0.05). Similarly, CD46 levels were higher in HT tissues than in control tissues. Bb, C4d, C3a and sC5b-9 serum levels were significantly increased in HT, GD and PTC patients compared with HDs (all P < 0.05).

CONCLUSION

Complement is overactivated in HT and PTC, but not in GD. All the three pathways are activated in HT, and the MBL and alternative complement pathways are activated in PTC. These distinct complement activation profiles may participate in HT, GD and PTC pathogenesis.

Autoantibodies against complement C1q correlate with the thyroid function in patients with autoimmune thyroid disease

Autoantibodies against complement C1q (anti-C1q) have been well described in patients with systemic lupus erythematosus, where they correlate with the occurrence of severe lupus nephritis. However, data on anti-C1q in organ-specific autoimmune diseases are scarce. In order to determine the prevalence of anti-C1q in patients with autoimmune thyroid disorders (AITD) and a possible association with thyroid function, we measured prospectively anti-C1q in 23 patients with Graves' disease (GD) and 52 patients with Hashimoto's thyroiditis (HT). Anti-C1q levels were correlated with parameters of thyroid function and autoantibodies against thyroperoxidase, thyroglobulin and thyroid stimulating hormone (TSH) receptor. Twenty-one patients with multi-nodular goitre and 72 normal blood donors served as controls. We found elevated concentrations of anti-C1q more frequently in patients with AITD than in controls: seven of 23 (30%) patients with GD and 11 of 52 (21%) patients with HT, compared with one of 21 (5%) patients with multi-nodular goitre and six of 72 (8%) normal controls. Anti-C1q levels did not correlate with thyroid autoantibodies. However, in GD absolute levels of anti-C1q correlated negatively with TSH and positively with free thyroxine (FT4) and triiodothyronine (FT3). In contrast, in HT, anti-C1q correlated positively with TSH levels. No correlation between TSH and thyroid autoantibodies was found. In conclusion, we found an increased prevalence of anti-C1q in patients with AITD and their levels correlated with the thyroid function in both GD and HT. This correlation seems to be independent of thyroid autoantibodies. Therefore, anti-C1q might point to a pathogenic mechanism involved in the development of AITD that is independent of classical thyroid autoantibodies.

The immunology of thyroid cancer

This article reviews the immunologic aspects of thyroid cancer, including thyroid-specific effector elements on thyroid cancer, and discusses the potential antigens, unique molecular markers, and transcription factors that could serve as targets for immunotherapy. The potential role of this type of treatment for thyroid cancer is examined also.

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.

Activated naive CD4+ peripheral blood T cells in autoimmune thyroid disease

To better understand the clinical significance of changes in lymphocytes in thyroid disease this study analyzed the proportion of CD19+, CD3+, CD4+ and CD8+ cells among circulating lymphocytes in Graves' disease (GD, n = 34) and autoimmune hypothyroidism (AH, n = 28) vs healthy subjects (n = 15). In addition, the expression of CD25 and CD45 isoforms on CD4+ T cells as well as their modulation by methimazole in patients with GD was measured using three color flow cytometry. It was observed that, irrespective of age, both patients with GD (17.6 +/- 7.0% +/- SD) and those with AH (19.0 +/- 9.5%) had an increased percentage of the CD25+CD45RA+ (naive) subpopulation of helper cells vs healthy subjects (7.9 +/- 2.3%, p < 0.0001). In patients with AH peripheral memory cells and hence overall CD25+ cells were more frequent among helper cells (56.7 +/- 12.2%) than in healthy subjects (40.8 +/- 14.0%, p < 0.001). Patients with GD (46.2 +/- 13.4%) did not differ from normal subjects in this respect. Treatment of GD with MMI reduced the percentage of CD25+CD45RA+ cells among CD4+ cells toward values seen in healthy subjects. In addition, we confirm previous reports that CD8+ cells toward values seen in healthy subjects. In addition, we confirm previous reports that CD8+ cells are significantly reduced in AH (23.9 +/- 4.9%) and untreated Graves' disease (23.2 +/- 6.6%) vs healthy subjects (32.2 +/- 5.9%, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and function of multiple regulators of complement activation in autoimmune thyroid disease

Membrane attack complexes of complement occur around thyroid follicles in Graves' disease and Hashimoto's thyroiditis. The lytic potential of such complexes is controlled by membrane-bound and fluid phase regulators and we have investigated the role of these in autoimmune thyroid disease. By immunohistochemical staining, clusterin and S-protein were found in all nine thyroid specimens from patients with Graves' disease and S-protein was found in one of two Hashimoto glands. CD46, CD55 and CD59 were found on thyroid cells in all specimens. CD46 and CD55 expression occurred on thyroid cells cultured in vitro and was increased significantly by culture with interleukin-1 (IL-1) and interferon-gamma (IFN-gamma), which are known to be released by the lymphocytic infiltrate in these conditions. Blocking CD55 had a weak and inconsistent effect on complement-mediated thyroid cell killing in vitro but, in four of five experiments, blocking CD46 enhanced killing. However, the effect of blocking CD59 was greater in all cases than blocking CD46 or CD55. Expression of these fluid phase and membrane-bound proteins may be important in determining the severity of thyroid damage produced by complement fixation in Graves' disease and Hashimoto's thyroiditis.

The potential immunological role of the thyroid cell in autoimmune thyroid disease

Over the last decade it has become evident that thyroid follicular cells express a number of immunologically active molecules in autoimmune thyroid disease that may endow them with the capacity to interact with cells of the classical immune system. Expression of major histocompatibility complex class II molecules is induced by gamma-interferon, but there is no evidence yet that thyroid follicular cells can concurrently express the costimulatory signals necessary for class II expression to result in T cell stimulation: in this situation, class II expression may have a protective role, inducing T cell anergy. Thyroid follicular cells also express a variety of cell surface proteins (in particular CD59) that may protect the cells from complement attack. On the other hand, the expression of adhesion molecules and cytokines by thyrocytes would seem to be harmful, as these are likely to exacerbate autoimmune injury. Further study of the immunological role of thyroid follicular cells will shed new light on the pathogenesis of Graves' disease and autoimmune hypothyroidism, and may lead to novel therapeutic approaches to these disorders.

Expression and function of membrane attack complex inhibitory proteins on thyroid follicular cells

Human thyroid cells are resistant to lysis by the homologous membrane attack complex. By immunohistochemical staining we here show that normal thyroid cells and those in Graves' disease and Hashimoto's thyroiditis express two membrane attack complex-inhibiting proteins, CD59 antigen and membrane attack complex-inhibiting protein/homologous restriction factor (MIP/HRF). In vitro, the expression of both molecules was enhanced by interleukin-1 (IL-1), tumour necrosis factor (TNF) and interferon-gamma (IFN-gamma) and cytokine-treated thyroid cells were more resistant to lysis by homologous complement. Blocking experiments with monoclonal antibodies against CD59 antigen and MIP/HRF showed that both molecules contributed but CD59 antigen was the more important in mediating resistance to complement attack. Expression of these proteins may be an important determinant of the severity of tissue injury produced by complement-fixing thyroid peroxidase antibodies in autoimmune thyroid disease.