IL-7 measures in controls and RA patients. (A) Circulating levels of interleukin (IL)-7 in healthy controls (HC, n = 80), disease-modifying anti-rheumatic drug (DMARD)-naïve (DN) rheumatoid arthritis (RA) with less than 6 months’ symptom duration (<6 m, n = 127), 6 to 24 months’ symptom duration RA (also DN, 6 to 24 m, n = 37), established long-lasting RA (RA, n = 55), clinical remission (CR, n = 90) osteoarthritis (OA, n = 19) and other disease controls (n = 96). All RA groups (<6 m DN, 6 to 24 m DN and RA) showed significantly reduced IL-7 levels (all P <0.005) compared to HC. (B) The ability to recover normal levels of IL-7 in CR was examined with respect to different clinical and demographic parameters. Lack of IL-7 recovery was significantly associated with patients in CR destined to flare within an 18-month follow-up period (P = 0.072) as well as with patient self-reported maternal family history of arthritis (P = 0.003). Age at disease onset was directly related to recovered IL-7 levels (rho = 0.539, P = 0.001). Black triangles are males and open triangles are females.