STAT3 and rheumatoid arthritis: The present results show that constitutive STAT3 phosphorylation is common in circulating leukocytes of patients with recent-onset untreated RA, associates with active disease when present in CD4+ T cells, associates with presence of erosions when present in CD8+ T cells, and identifies a patient group designated by the presence of systemic inflammation and good response to treatment with synthetic DMARDs when present in CD4+ T cells.