Phenotypic and functional characteristics of early thymic cells migrating to peripheral blood under normal conditions and in autoimmune disorders

Complex mechanisms of thymus functioning affect its structural matrix thus promoting gradual accumulation of genetic mutations, changes in gene expression and premature immunosenescence. The study of early thymic cell migrants (ETM) is necessary to identify possible diagnostic biomarkers and potential checkpoints of autoimmune diseases (AID). We have studied peripheral blood samples of patients with rheumatoid arthritis (RA), psoriatic arthritis (PsA), psoriasis (PS) and healthy donors. The aim of the study was to assess the ratio of recent cell migrants from the thymus and circulating naïve T regulatory cells in healthy persons and autoimmune diorders. The relative numbers of recent thymic migrants CD4+CD45RA+CD31+ (ETM), and the contents of FoxP3+T regulatory cells (Treg) in this population were determined by flow cytometry. The number of proliferating cells was determined by intracellular Ki-67 marker. The results show that the number of ETM was reduced in the group of patients with RA and patients with PsA compared with the healthy donor group (17.3%, 18.6% vs. 23.6%), and did not change significantly in patients with psoriasis. There were no significant differences between donors and patients with AIDs on the contents of proliferating ETM and Tregs. The proliferation rates of T regulatory cells in patients with psoriatic pathology were comparable to donor values, with a trend for its increase in RA patients. The numbers of proliferating naive FoxP3+Tregs in RA patients was significantly higher than the numbers of proliferating ETM (15.8% vs 3.1%, p 0.05, respectively). A decrease in relative number of ETM in AID may be associated with activation of T lymphocytes and higher proportion of central memory T cells. The number of Tregs among ETM, and their proliferation rates in patients with psoriatic disorder suggest the absence of disturbed Treg generation in thymus. The ambiguous results obtained in patients with RA are of potential significance for diagnostics and therapy. However, they require additional confirmation in a larger sample of patients.