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Endocrine Diseases: . Mechanism of development of Autoimmune endocrine disease : Two factors could be involved in development of human autoimmune disorders: 1-Expression of Class II HLA (human leukocyte antigen) on the surface of target endocrine cells.
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Endocrine Diseases: Mechanism of development of Autoimmune endocrine disease: Two factors could be involved in development of human autoimmune disorders: 1-Expression of Class II HLA (human leukocyte antigen) on the surface of target endocrine cells. Infectious agent Inflammatory cells chemotaxis(INFγ) Expression of HLA Presentation of own cellular proteins; reactive T and B cell response.
N 2-The antigen Cross-reactivity: external organic material or infectious agents epitopesShow antigenic cross- reactivity with target tissues. formation of Auto-reactive Humoral immune response antibodies. Tissue destruction.
Thyroid Autoimmune Diseases:Chronic Thyroiditis: (Hashimoto’s thyroiditis): Definition: It is an autoimmune disease in which the thyroid gland is attacked by a variety of cell- and antibody-mediated immune processes. General considerations: -Family history of thyroid disease and HLA gene polymorphism (DR4, DR5). -Most common in middle-aged and elderly patients. -Females make up the vast majority of patients (85%).
N Major Immunologic features of Hashimoto’s thyroiditis: 1-The lymphocytic infiltration of the thyroid gland. 2-The Antibodies against thyroid antigens are present. 3-The cellular sensitization to thyroid antigens. Germinal center: lymphocyte infiltrate. Pink reactive dying thyroid cell : Immunohistochemistry for P63. with cytoplasmic-acidophilic granules. :Positive in Germinal center (H.T).
N Pathogenesis mechanism in Hashimoto’s thyroiditis: -Various Autoantibodies are present against thyroid peroxidase, and thyroglobulin. -Sensitization of Thyroid tissue ( thyrocyte). -CD8 and NK cell hyperactivity by ADCC (Antibody-Dependent Cell-Mediated Cytotoxicity)mechanism. -Apoptosis of thyrocyte. -CD4 response, and chemotaxis of macrophage.
Clinical Features of chronic thyroiditis: Primary stage: -Clinical hyperthyroidism due to inflammatory breakdown of thyroid follicles. Late stage: -Hypothyroidism due to progressive destruction of thyroid tissue and cellular malfunction. -The most common outcome of Hashimoto’s disease is the hypothyroidism.
Signs and Symptoms of Chronic thyroiditis: -A consistent physical sign seen in Hashimoto’s disease is an enlarged thyroid gland (Goiter). -Often, lymph nodes surrounding the gland become enlarged. -Rarely, Symptoms of generalized vasculitiswith urticaria and nephritis could be seen due to presence of circulating immune complexes.
Differential diagnosis of Chronic thyroiditis: -The hallmark of the diagnosis of this disease is the presence of circulating Autoantibodies: 1-Anti-thyroglobulin antibodies. 2-Anti-thyroid peroxidase antibodies. -These antibodies show a sensitivity of 90% and detected by: 1-Immunofluorescenceassay. 2-ELISA. 3-Agglutinationassay. -In patients without serum antibodies, autoantibodies are localized in intrathyroidal lymphoid follicles.
Graves’ Disease: Definition: -It is an autoimmune disease where the thyroid is activated by anti-TSHreceptorautoantibodies to produce excessive amount of thyroid hormones. -The most common cause of hyperthyroidism (60-90% of all cases). -It has a powerful hereditary component, affects up to 2% of the female population, and is between five and ten timesas common in females as in males.
n General Considerations: -Hyperthyroidism and thyrotoxicosis with a diffuse goiter. - About 30-50% of people with Graves' disease will also suffer from Graves' ophthalmopathy caused by inflammation of the eye muscles by attacking autoantibodies. The orbit around the eye: upper eyelid retraction, edema, erythema, and Graves’ Goiter: hyperthyroidism conjunctivitis.
N -Specific cross-reactivity between some microbes (Viruses; Coxsackievirus, and bacteria; Yersinia) and TSH-Receptor of thyroid follicular cells. -Strong association with DR3, DQα , and DQβgenotype of MHC II haplotypes. -Family History: The disease is associated with different types of generalized autoimmune susceptibility; such as Hashimoto’s disease and antibodies to gastric intrinsic factor.
N Major Immunologic features of Graves’ disease: 1-Antibodies against thyroid antigen are present; that stimulate thyroid cell function. 2-Class II HLA expression on the surface of thyroid cells. 3-Associated autoimmune ophthalmopathy.
Pathogenesis mechanism of Graves’ disease: -Autoantibodies present against TSH-receptor: 1- Thyroid-stimulating immunoglobulins (TSI): Activate TSH-receptor; elevated thyroid hormones. 2-Thyroid growth immunoglobulins( TGI) : Growth of thyroid follicles. 3-Thyroidbinding-inhibitingimmunoglobulins (TBII) : Inhibits TSH binding. -No Cellular immune response; Histology show no destruction of thyroid tissues. -Colloid suspension show lymphocytic infiltration: CD4, CD8, and B lymphocytes.
Diagnosis of Graves’ disease: -Clinically: Signs and symptoms of hyperthyroidism. -Radiology: Increased uptake of radioactive iodine. -Serology: A-Elevated Total and free T4, and T3. B-Identification of Anti-thyroid antibodies in patient’s sera: 1-Antibodies that activatecellular cAMP; Thyroid stimulating Immunoglobulin (TSI). 2-Thyroid growth stimulating immunoglobulins (TGI). 3-Antibodies that displace the binding of TSH from its receptor (TBII).
N Anti-thyroid antibodies could be detected by: 1-ELISA Test: Microtiter plate wells should be coated by recombinant Human TSH-receptors. 2-Tissue culture (Fisher Rat thyroid cell line 5): -It can be used to measure the presence and activity of Anti-thyroid antibodies ( IgG) in patient's sera. -Serum specimens should be incubated with cell line culture; then : The cAMP activity and the incorporation of radioactivethymidine are measured.
