CD4 and synovial sarcoma: To examine the baseline (or steady state) as well as antigen-stimulated expression pattern of Th9 cells in Ss infections, we cultured whole blood from INF and UN individuals with media alone or with SsAg, NIE, PPD or P/I and measured the frequency of CD4+ T cells expressing IL-9 or co-expressing IL-9, IL-4 or IL-10.