Thyroid Infiltrating T Lymphocytes in Hashimoto’s Thyroiditis: Phenotypic and Functional Analysis at Single Cell Level
In the last 30 years, studies of the thyroid-specific abnormal autoimmune response have mainly focused onto humoral rather than cellular mechanisms. Thus, both the initial events responsible for the breakdown in self-tolerance and the subsequent immunological mechanisms responsible for thyroid infiltration by lymphocytes and thyroid cell alterations are still poorly understood. The development of monoclonal antibodies (MoAbs) to lymphocyte membrane antigens made it possibile to analyze the phenotype of thyroid infiltrating lymphocytes by immunohistological staining techniques. Both B and T lymphocytes have been found in affected glands, the major cellular component being T cells. Some controversy, however, existed about the proportion of the CD4+and CD8+T cell subsets within autoimmune thyroid infiltrates. A reduction in intrathyroidal CD8+cells compared with peripheral blood(PB)1 or a substantial identity between PB and thyroid infiltrates with regard to the proportions of CD4+and CD8+ cells have been reported2j3.However, more recent studies agree that T cells with the CD8+ cytotoxic/suppressor phenotype are predominant in either Graves’ disease(GD) or Hashimoto’s thyroiditis (HT) infiltrates S5>6. In any case,whatever the alteration of phenotypically defined T cell population may be, it is of uncertain significance. Since it is now clear that CD4 and CD8 antigens do not represent markers of specific functions, before any conclusion is drawn on the role of a given cell population, phenotypic analysis needs to be supported by functional studies. Unfortunately, functional assays performed on heterogeneous cell populations are difficult to interpret, because they do not provide information on the proportion of cells expressing a given function.
KeywordsCell Clone Cytolytic Activity Normal Peripheral Blood Clonal Progeny Immune Interferon
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