Moreover, together with alterations in other markers of thymopoiesis which have been reported to occur predominantly in younger patients with MS, such RGFP966 as reduced content of signal joint T-cell
receptor excision circles (sjTRECs) in peripheral T cells, decreased numbers of circulating RTEs defined by surface expression of CD31 and accelerated exit of CD4+ RTEs from the thymus as reflected by increased expression of CXCR4 in naïve and RTE CD4+ T-cell subsets, favor the hypothesis that premature thymic involution and immunosenescence play a role in disease pathogenesis 2–4, 6, 30. Autoimmunity associated with rheumatoid arthritis, systemic sclerosis (SS), and MS has been reported to concur with slow recovery of CD4+ T-cell counts after iatrogenic lymphopenia 31. Whereas a lacking IL-7 response accounts for this phenomenon in RA 31, it is buy FK506 thus far unexplained why T-cell immune reconstitution is delayed in patients with MS after therapeutic lymphocyte depletion with alemtuzumab (Campath-1H) 32, 33. The overall reduced IL-7Rα-expression on total Tconv and Tconv subsets in patients compared to healthy donors, as demonstrated in this study is well in line with the postulated failure in lymphocyte homeostasis. In lymphopenic patients
with MS this condition is likely to account for slower IL-7/IL-7R driven homeostatic lymphocyte proliferation and expansion. While the IL-7 response induced by lymphopenia following autologous stem cell transplantation 34 or alemtuzumab treatment 33 as next well as basal pretreatment serum IL-7 levels were reported to be unaltered in patients with MS and systemic sclerosis, we detected elevated plasma IL-7 concentrations in our cohort of patients with an established relapsing remitting type of disease. Since MS patients are not lymphopenic, we speculate that the production of IL-7 by non-hematopoietic stroma cells is upregulated as a consequence of the reduced
availability of IL-7Rα on patient-derived Tconv. In favor of this hypothesis, we found an inverse correlation between IL-7 levels and IL-7Rα-MFIs on total Tconv. Finally, we assessed the relative frequency of the rs6897932-SNP [T244I] located in exon 6 of the IL-7RA locus, which has been independently confirmed to be associated with MS 15–17 and also influences the risk of type 1 diabetes 18 and chronic inflammatory arthropathies 19. In agreement with the results reported in several large genetic association studies, the (C) allele encoding threonine instead of isoleucine at amino acid position 244 was enriched among patients and detectable in 74.7 versus 79.5% individuals in the groups of HC and patients respectively.