CXCR5 and rheumatoid arthritis: Currently, peripheral blood CXCR5-expressing Treg cells were studied in a very limited number of human diseases; in the first instance, they were studied in patients with autoimmune disorders, including ankylosing spondylitis [25], rheumatoid arthritis [26], multiple sclerosis [27], and many others diseases, including such viral infections as HIV [28], influenza [29] etc., but the biological importance of these cells in humans remains unclear so far.