Circulating IL-7 levels are directly correlated with the TREC content of CD4+ T-cells in rheumatoid arthritis (RA) patients in clinical remission. (a) The T-cell receptor excision circle (TREC) content of total CD4+ T-cells, measured in patients in clinical remission (n = 36, all triangles [Table 1]), is heterogeneous, ranging from values observed in healthy control individuals to values in active RA patients. Using the age relationship to TREC content in healthy control individuals (black circles and thin line, correlation coefficient R = -0.816, P < 0.00001; previously reported ), two groups of patients can be differentiated: group 1 exhibits TREC content similar to or greater than that in age-matched healthy control individuals; and group 2 exhibits lower TREC content. We used the median value for TREC content to separate patients into two groups. We refer to these two groups as group 1 (G1; above median value, indicated by black triangles) and group 2 (G2; below median value, indicated by open triangles). The age relationship to TREC content is recovered only in group 1 (thick line; correlation coefficient R = -0.738, P = 0.001; for group 2 R = 0.341, P = 0.174). (b) Circulating IL-7 levels are directly correlated with TREC content of CD4+ T-cells in 36 patients in clinical remission (R = 0.777, P < 0.00001). In addition, patients satisfying the American College of Rheumatology (ACR) criteria for remission are indicated by open diamonds and patients not satisfying the ACR criteria by closed diamonds (Table 3). These two groups are undistinguishable.