Supplementary Material for: Interactions of Lymphocytes, Thyrocytes and Fibroblasts in Hashimoto’s Thyroiditis: An Immunohistochemical and Ultrastructural Study

<i>Background:</i> The mechanism of autoimmune reaction, a diffuse process consisting of a combination of epithelial cell destruction, lymphoid cellular infiltration, and fibrosis in Hashimoto’s thyroiditis, is not well known. The aim of this study was to analyse the cell subsets in thyroid tissue of patients with Hashimoto’s thyroiditis. <i>Methods:</i> We studied paraffin-embedded thyroid specimens obtained from children with Hashimoto’s thyroiditis and children without an autoimmune thyroid disease. Mononuclear T cells were detected by means of CD3+, CD4+, CD8+ antibodies, B cells by CD79 alpha+ antibodies, and antigen-presenting cells by CD1a+ antibodies, and they were counted in every 1,000 cells. The specimens from each patient were routinely estimated and investigated under the electron microscope. <i>Results:</i> In Hashimoto’s thyroiditis, we observed a statistically significant increase in T suppressor/cytotoxic cells CD8+ (20.54 ± 0.68%) in comparison to the control group (0.65 ± 0.30%), simple goitre (4.01 ± 5.54%) and nodular goitre (8.53 ± 2.37%), and a statistically significant increase in plasma CD79 alpha+ cells (31.65 ± 9.11%) in comparison to the control group (4.11 ± 1.94%), simple goitre (1.83 ± 0.64%) and nodular goitre (5.22 ± 1.63%). Simultaneously, we observed a low number of CD4+ T helper cells in the thyroid gland (0.93 ± 0.99%) in Hashimoto’s thyroiditis (0.19 ± 0.05% in the control group, 1.05 ± 2.71% in simple goitre, 2.03 ± 1.06% in nodular goitre). The ultrastructural investigations showed interactions between T cells, plasmocytes, fibrocytes and thyrocytes leading to apoptosis of thyrocytes. An immunological synapse between T cells, plasmocytes and thyrocytes in the thyroid gland was noticed. <i>Conclusions:</i> In Hashimoto’s thyroiditis, autoantigen presentation in combination with a low number of CD4+ T helper cells and a high number of CD8+ cells and plasmocytes caused the development of a cytotoxic reaction against thyrocytes, leading to apoptosis of the thyrocytes.