CD20 + T lymphocytes in isolated Hashimoto's thyroiditis and type 3 autoimmune polyendocrine syndrome: a pilot study

CD20⁺ T cells represent up to 5% of circulating T lymphocytes. These cells have been shown to produce higher levels of IL-17A and IFN-γ than those of CD20^- T lymphocytes. Some reports described the role of CD20⁺ T cells in autoimmune disorders such as multiple sclerosis and rheumatoid arthritis possibly due to their ability to produce these inflammatory cytokines. This study is aimed at describing the behavior of CD20⁺ T lymphocytes in the most frequent autoimmune disorder, i.e., Hashimoto's thyroiditis (HT), presenting isolated or associated to further autoaggressive disorders in a frame of poly-autoimmunity.

The study group encompasses 65 HT patients: 23 presenting in isolated form (IT) and 42 with an associated non-endocrine autoimmune disorder [16 with chronic atrophic gastritis (CAG), 15 with nonsegmental vitiligo (VIT), and 11 with celiac disease (CD)]. Twenty healthy donors act as control group (HD). Chronic use of interfering drugs, severe or chronic disorders, and pregnancy and lactation were used as exclusion criteria. Whole blood samples (100 µl) were stained with fluorescent-labeled antibodies (anti-CD45, anti-CD3, anti-CD19, anti-CD16, anti-CD56, anti-CD4, anti-CD8, anti-CD20). Red blood cells were then lysed by adding 1 ml of hypotonic buffer, and samples were acquired on a Flow Cytometer.

CD3⁺CD8⁺CD20⁺ T lymphocytes' percentages, were significantly higher in the whole group of autoimmune patients compared to healthy donors (p = 0.0145). Dividing HT patients based on the type of presentation of autoimmune thyroiditis, CAG group showed the highest percentage of these cells as compared to HD and CD (p = 0.0058). IT patients showed higher percentages of CD3⁺ CD8⁺CD20⁺ cells than those of HD patients although not reaching statistical significance. However, dividing IT group based on thyroid function, hypothyroid patients showed higher CD8⁺CD20⁺ cell percentages than those of HD and euthyroid patients (p = 0.0111). Moreover, in IT patients, these cells were negatively correlated with FT4 levels (p = 0.0171; r = -0.4921).

These preliminary findings indicate that CD8⁺CD20⁺ T cells are activated in patients with autoimmune thyroiditis and may behave differently according to the presence of poly-autoimmunity and hypothyroidism.