In addition, differences in cell frequencies, inflammatory protein levels, and gene expression can be detected in children who will develop more severe disease, before extension occurs: for example, in the so-called “extended-to-be” group of cases, the CD4:CD8 ratio in synovial fluid is lower and the levels of the chemokine CCL5 are higher in extended-to-be oligoarticular JIA compared with persistent oligoarticular JIA [15•]. The gene discussed is CD4; the disease is juvenile idiopathic arthritis.