Background
Despite the accumulation of evidence that CD4+CD25high regulatory T cells play an important role in the prevention of autoimmune disease, little is known about how they are regulated in vivo. There are thought to be at least two mechanisms for the generation of regulatory T cells: naturally occurring CD4+CD25high regulatory T cells derive from the thymus, and peripherally-induced regulatory cells arise under tolerogenic conditions. Recently, cytokine activation requirements for CD4+CD25high regulatory T-cell function were associated with IL-7, as well as IL-2 and IL-4. We examined a cohort of patients with rheumatoid arthritis whose disease was well controlled, and where we had previously shown that heterogeneous circulating levels of IL-7 positively correlated with thymic activity, to investigate the role of IL-7 on the function of CD4+CD25high T cells.