Despite the peripheral enrichment of FOXP3+ T cells in our severe HT patients, thyroid inflammation is obviously still not suppressed, thus supporting the concept of a profound insufficiency of CD4+FOXP3+ Treg cells in autoimmunity, previously also reported in rheumatoid arthritis [30], inflammatory bowel disease [31], and Graves' disease [27]. Here, CD4 is linked to rheumatoid arthritis.