IL15 and rheumatoid arthritis: We show that GM-CSF production by human CD4+ T cells is enhanced by the Th1-polarising cytokine IL-12 and the T-cell survival factor IL-15 and confirms the recent findings by Noster et al35 This correlates with the cytokine environment CD4+ T cells are likely to encounter in vivo and may explain our finding that ex vivo RA synovial T cells produce more GM-CSF than RA or healthy control PB CD4+ T cells.